Lipids | Biology | Visionlearning

<!DOCTYPE html> <html lang="en" dir="ltr"> <head>  <meta http-equiv="X-UA-Compatible" content="ie=edge"> <meta charset="utf-8"> <base href="https://www.visionlearning.com"> <title>Lipids | Biology | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/biology/2/lipids/207"> <meta name="description" content="Fats, oils, waxes, steroids, certain plant pigments, and parts of the cell membrane – these are all lipids. This module explores the world of lipids, a class of compounds produced by both plants and animals. It begins with a look at the chemical reaction that produces soap and then examines the chemical composition of a wide variety of lipid types. Properties and functions of lipids are discussed."> <meta name="keywords" content="science, education, STEM, math, biology, chemistry, physics, earth science, online learning"> <meta name="viewport" content="width=device-width, initial-scale=1.0, shrink-to-fit=no"> <meta name="msvalidate.01" content="D8E20F39AD48052260032E56DE409970"> <script type="application/ld+json"> { "@context": "http://schema.org/", "@type": "Article", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://visionlearning.com/en/library/biology/2/lipids/207" }, "name": "Lipids", "headline": "Lipids: Composition, structure, and function", "author": [ { "@type": "Person", "name": "Nathan H Lents, Ph.D." } , { "@type": "Person", "name": "Lizzie Stark, M.S./M.F.A" } , { "@type": "Person", "name": "Bonnie Denmark, M.A./M.S." }], "datePublished": "2014-12-04 08:37:44", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_207-23061209062411.jpg", "width": 696, "height": 464 }, "publisher": { "@type": "Organization", "name": "Visionlearning, Inc.", "logo": { "@type": "ImageObject", "url": "http://visionlearning.com/images/logo.png", "width": 278, "height": 60 } }, "description": "Fats, oils, waxes, steroids, certain plant pigments, and parts of the cell membrane – these are all lipids. This module explores the world of lipids, a class of compounds produced by both plants and animals. It begins with a look at the chemical reaction that produces soap and then examines the chemical composition of a wide variety of lipid types. Properties and functions of lipids are discussed.", "keywords": "science, education, STEM, math, biology, chemistry, physics, earth science, online learning", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2014"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/biology/2/lipids/207"> <meta property="og:title" content="Lipids | Biology | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="Fats, oils, waxes, steroids, certain plant pigments, and parts of the cell membrane – these are all lipids. This module explores the world of lipids, a class of compounds produced by both plants and animals. It begins with a look at the chemical reaction that produces soap and then examines the chemical composition of a wide variety of lipid types. Properties and functions of lipids are discussed."> <meta property="og:image" content="https://visionlearning.com/images/logo.png"> <meta property="fb:admins" content="100000299664514"> <link rel="stylesheet" type="text/css" href="/css/visionlearning.css">  <link rel="stylesheet" type="text/css" href="/css/visionlearning-icons.css">  <link rel="preconnect" as="font" href="https://fonts.gstatic.com" crossorigin> <link href="https://fonts.googleapis.com/css2?family=Open+Sans:ital,wght@0,400;0,700;1,400;1,700&family=Schoolbell&display=swap" rel="stylesheet"> <style> textarea.myEditor { width: 90%; height: 350px; } </style> <script type="text/x-mathjax-config" src="/js/mathjax-config.js"></script> <script id="MathJax-script" async src="/js/mathjax/tex-svg.js"></script> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script> </head> <body>  <header class="box-shadow-1" id="global-header"> <div class="theme-light text-align-center"> <a class="focusable-only" href="#skip-header-target"> Jump to main content </a> <a class="focusable-only" href="#global-footer"> Jump to website footer </a> </div> <div class="border-bottom"> <div class="vl-hat font-size-md wide margin-x-auto"> <div class="vl-hat__toggle-button"> <button class="button button--icon-only mobile-menu-toggle" aria-label="Menu" data-toggle="collapse" data-target-toggle="#vl-hat-nav"> <span class="icon icon-menu" aria-hidden="true"></span> </button> </div> <nav class="vl-hat__menu" id="vl-hat-nav"> <ul class="nav nav--horizontal--xl"> <li><a href="/en/about">About</a></li> <li><a href="/en/help">Contact</a></li> <li><a href="/en/about/jobs">Jobs</a></li> <li><a href="/en/user/registration">Register</a></li> </ul> </nav> <div class="vl-hat__actions"> <button class="button button--icon-only" aria-label="Search" data-toggle="collapse" data-target-toggle="#global-search" data-target-close="#vl-hat-nav" aria-expanded="false"> <span class="icon icon-search" aria-hidden="true"></span> </button> <a class="button button--has-icon" href="/en/user/signin"> <span class="icon icon-sign-in"></span> <span class="button__text">Sign In</span> </a> <a class="button" href="/es/library/Biologia/2/Lípidos/207/reading" id="es-translate" onclick="setCookie('lang', 'es', 1); window.location.href='/es/library/Biologia/2/Lípidos/207/reading';"><span>Español</span></a> </div> </div> </div>  <div class="collapse padding-y-3 border-bottom" id="global-search" data-focus-first> <div class="container narrow"> <form action="/en/search" aria-label="Search" method="post"> <div class="form-entry"> <div class="form-entry__field "> <span class="form-entry__field__input"> <input type="text" name="query" id="search-input" autocomplete="off"> <button class="button theme-dark" data-clear-input> Search</button> </span> </div> </div> </form> </div> </div>  <div class="vl-header wide margin-x-auto"> <div class="vl-header__logo"> <a href="/en/" data-logo="brand"> <svg xmlns="http://www.w3.org/2000/svg" width="270" height="60" viewBox="0 0 270 60"> <g> <circle cx="26.0869" cy="18.4451" r="9"/> <polygon points="0 20.895 0 45.177 26.138 60 52.173 45.177 52.173 20.895 26.138 35.718 0 20.895"/> <path d="M3.7129,18.128a24.3466,24.3466,0,0,1,44.7541-.1145l2.2291-1.2711.6723-.3855a27.8159,27.8159,0,0,0-5.6743-8.2194,27.6219,27.6219,0,0,0-39.157,0A27.7845,27.7845,0,0,0,.805,16.48l.46.2605Z"/> </g> <g> <polygon points="74.18 31.639 83.362 8.186 78.7 8.186 71.621 27.138 64.542 8.186 59.881 8.186 69.064 31.639 74.18 31.639"/> <rect x="83.1631" y="14.655" width="3.6794" height="16.9836"/> <path d="M93.0481,19.2605c0-1.195,1.1924-2.1079,3.1189-2.1079a6.89,6.89,0,0,1,5.0119,2.0388l1.542-2.6018a9.6485,9.6485,0,0,0-6.553-2.3562c-4.2749,0-6.6588,2.3572-6.6588,5.1345,0,6.5391,10.2333,4.1492,10.2333,7.489,0,1.335-1.156,2.25-3.365,2.25a8.6789,8.6789,0,0,1-5.7109-2.355L88.9834,29.388A10.2351,10.2351,0,0,0,96.2365,32.06c4.557,0,7.0455-2.2866,7.0455-5.3095C103.281,20.001,93.0481,22.251,93.0481,19.2605Z"/> <path d="M107.7051,12.581a2.285,2.285,0,1,0-2.2786-2.2851A2.2763,2.2763,0,0,0,107.7051,12.581Z"/> <rect x="105.8479" y="14.655" width="3.6797" height="16.9836"/> <path d="M120.302,14.2329c-5.3979,0-8.6919,4.0085-8.6919,8.896,0,4.853,3.294,8.9316,8.6919,8.9316s8.69-4.0786,8.69-8.9316C128.9919,18.24,125.698,14.2329,120.302,14.2329Zm0,14.5561c-3.1194,0-4.8706-2.6359-4.8706-5.66,0-2.9878,1.7512-5.625,4.8706-5.625,3.1545,0,4.87,2.636,4.87,5.625C125.1719,26.1541,123.4561,28.79,120.302,28.789Z"/> <path d="M134.75,19.7539a5.7679,5.7679,0,0,1,4.35-2.25c2.0674,0,3.4336.844,3.4336,3.5171V31.6387h3.6782V19.6831c0-3.48-1.8217-5.4492-5.4683-5.4492a8.0608,8.0608,0,0,0-5.9926,2.708V14.655h-3.679V31.6387h3.679V19.7539Z"/> <rect x="149.3125" y="8.1861" width="3.6777" height="23.4526"/> <path d="M164.289,29.0359a5.1266,5.1266,0,0,1-5.3627-4.677h13.038v-.9138c0-5.344-3.2241-9.2122-8.3051-9.2122a8.57,8.57,0,0,0-8.5859,8.896,8.5025,8.5025,0,0,0,8.8656,8.9316,10.009,10.009,0,0,0,6.8692-2.4966l-1.6845-2.4269A7.0854,7.0854,0,0,1,164.289,29.0359Zm-.664-11.7778a4.563,4.563,0,0,1,4.8,4.4665H158.893A4.6378,4.6378,0,0,1,163.625,17.2581Z"/> <path d="M184.8681,29.7749v1.8638h-.0009v.0044h3.6792V20.354c0-4.5362-3.295-6.1179-7.08-6.1179a9.893,9.893,0,0,0-7.1113,2.7429l1.5429,2.5669a6.7609,6.7609,0,0,1,5.0127-2.18c2.3115,0,3.958,1.197,3.958,3.1645v2.533a7.0556,7.0556,0,0,0-5.5009-2.1809c-2.7706,0-5.8545,1.6169-5.8545,5.554a5.6418,5.6418,0,0,0,5.8545,5.6244A7.11,7.11,0,0,0,184.8681,29.7749Zm-7.6748-3.3059c0-1.8284,1.58-3.0574,3.6455-3.0574a5.0388,5.0388,0,0,1,4.0289,1.7578v2.6021a5.0426,5.0426,0,0,1-4.0289,1.7581C178.7715,29.5291,177.1933,28.332,177.1933,26.469Z"/> <path d="M195.3271,20.07a5.7666,5.7666,0,0,1,4.38-2.2847,5.0479,5.0479,0,0,1,1.1211.1052V14.2334a7.34,7.34,0,0,0-5.501,2.8845V14.655h-3.6806V31.6387h3.6806Z"/> <path d="M214.1543,31.6387h3.6772V19.6831c0-3.48-1.8232-5.4492-5.47-5.4492a8.063,8.063,0,0,0-5.9907,2.708V14.655h-3.6826V31.6387h3.6826V19.7539a5.7656,5.7656,0,0,1,4.3462-2.25c2.07,0,3.4375.844,3.4375,3.5171V31.6387Z"/> <path d="M222.7871,12.581a2.285,2.285,0,1,0-2.2778-2.2851A2.28,2.28,0,0,0,222.7871,12.581Z"/> <rect x="220.9316" y="14.655" width="3.6792" height="16.9836"/> <path d="M237.3779,14.2339a8.0487,8.0487,0,0,0-5.9893,2.708V14.655H227.708V31.6387h3.6806V19.7539a5.76,5.76,0,0,1,4.3453-2.25c2.0688,0,3.4355.844,3.4355,3.5171V31.6387h3.68V19.6831C242.8476,16.2031,241.0234,14.2339,237.3779,14.2339Z"/> <path d="M257.8613,17.0105a6.6416,6.6416,0,0,0-5.4311-2.7771c-4.3853,0-7.5,3.1992-7.5,8.719,0,5.592,3.1875,8.72,7.5,8.72a6.8079,6.8079,0,0,0,5.4311-2.8483v1.9343c0,3.6211-2.5937,4.7461-5.01,4.7461a6.6654,6.6654,0,0,1-5.3974-2.1807l-1.72,2.6743a9.68,9.68,0,0,0,7.1171,2.5308c4.1329,0,8.6885-1.6509,8.6885-7.77V14.655h-3.6806v2.356h.0019Zm0,9.11a5.6127,5.6127,0,0,1-4.3452,2.25c-2.9492,0-4.8057-2.146-4.8057-5.417s1.86-5.4492,4.8057-5.4492a5.6143,5.6143,0,0,1,4.3452,2.25Z"/> <path d="M266.75,8.0105a3.2728,3.2728,0,0,0-3.2715,3.2724v.0176A3.2608,3.2608,0,1,0,270,11.2829v-.019A3.2387,3.2387,0,0,0,266.75,8.0105Zm2.9062,3.2724A2.918,2.918,0,1,1,263.82,11.3v-.0175a2.9183,2.9183,0,1,1,5.8364-.0186v.019Z"/> <path d="M268.2588,10.5781V10.56a.9471.9471,0,0,0-.2784-.7132,1.4069,1.4069,0,0,0-1.0351-.3718h-1.5225V12.9h.6494V11.716h.7134l.8277,1.1839h.7719l-.9184-1.292A1.0169,1.0169,0,0,0,268.2588,10.5781Zm-1.34.5679-.8467-.002V10.06h.8467c.4229,0,.6773.19.6773.5324v.0215C267.5957,10.9389,267.3418,11.146,266.9189,11.146Z"/> </g> <g> <path d="M66.4861,52.55a1.7859,1.7859,0,0,0,.6358.124,1.077,1.077,0,0,0,1.1162-.7908l.4961-1.1315-3.1319-7.5655h1.2559l2.4961,6.1392,2.48-6.1392h1.271l-3.7514,9.0071a2.2266,2.2266,0,0,1-2.2017,1.5193,3.7739,3.7739,0,0,1-.8525-.1084Z"/> <path d="M74.0345,46.9222a3.7111,3.7111,0,1,1,7.41,0,3.7119,3.7119,0,1,1-7.41,0Zm6.1855,0a2.5154,2.5154,0,1,0-4.9766,0A2.62,2.62,0,0,0,77.74,49.8214C79.3362,49.8214,80.22,48.4571,80.22,46.9222Z"/> <path d="M88.5432,50.6739V49.62a3.663,3.663,0,0,1-2.6665,1.24A2.1059,2.1059,0,0,1,83.49,48.4725V43.1861h1.1626v4.93c0,1.3179.6665,1.7056,1.6743,1.7056A2.865,2.865,0,0,0,88.5432,48.69V43.1861h1.1626v7.4878Z"/> <path d="M92.1848,50.6739V43.1861h1.1626v1.209a3.1828,3.1828,0,0,1,2.4961-1.3642v1.1938a2.0528,2.0528,0,0,0-.4653-.0464,2.7388,2.7388,0,0,0-2.0308,1.1936v5.302Z"/> <path d="M101.4065,41.14a.783.783,0,0,1,1.5659,0,.783.783,0,1,1-1.5659,0Zm.2017,9.5342V43.1861h1.1626v7.4878Z"/> <path d="M110.305,50.6739V45.775c0-1.3179-.667-1.7363-1.6744-1.7363a2.8928,2.8928,0,0,0-2.2172,1.1626v5.4726h-1.1626V43.1861h1.1626v1.085A3.7155,3.7155,0,0,1,109.08,43a2.1281,2.1281,0,0,1,2.3872,2.4184v5.2554Z"/> <path d="M113.9,48.8446a3.3932,3.3932,0,0,0,2.4648,1.07c1.1475,0,1.7676-.5115,1.7676-1.24,0-.8215-.915-1.0849-1.9224-1.333-1.2714-.2947-2.7133-.6357-2.7133-2.186,0-1.1626,1.0078-2.1548,2.791-2.1548a3.79,3.79,0,0,1,2.7749,1.085l-.5425.8061a2.9179,2.9179,0,0,0-2.2324-.9456c-1.0235,0-1.6592.4651-1.6592,1.1316,0,.7288.8525.9615,1.83,1.1939,1.3022.2944,2.8061.6665,2.8061,2.3254,0,1.2556-1.0078,2.2635-2.9458,2.2635a3.9829,3.9829,0,0,1-3.0229-1.1783Z"/> <path d="M121.1067,41.14a.783.783,0,0,1,1.5659,0,.783.783,0,1,1-1.5659,0Zm.2017,9.5342V43.1861h1.1626v7.4878Z"/> <path d="M125.5247,51.7281a2.8594,2.8594,0,0,0,2.4341,1.0232,2.1439,2.1439,0,0,0,2.4028-2.2478v-1.07a3.1273,3.1273,0,0,1-2.5117,1.3332c-1.9531,0-3.333-1.4572-3.333-3.8757,0-2.4028,1.3642-3.8911,3.333-3.8911a3.1026,3.1026,0,0,1,2.5117,1.3176V43.1861h1.1626v7.2708c0,2.48-1.7363,3.2556-3.5654,3.2556a3.8254,3.8254,0,0,1-3.023-1.1162Zm4.8369-6.48a2.7589,2.7589,0,0,0-2.2324-1.2092c-1.5039,0-2.4029,1.1938-2.4029,2.8525,0,1.6433.899,2.8525,2.4029,2.8525a2.7724,2.7724,0,0,0,2.2324-1.2246Z"/> <path d="M139.0725,50.6739v-4.93c0-1.3176-.6826-1.7053-1.69-1.7053a2.9439,2.9439,0,0,0-2.2173,1.1626v5.4726h-1.1626v-10.34h1.1626v3.9375A3.7225,3.7225,0,0,1,137.8474,43a2.106,2.106,0,0,1,2.3877,2.3872v5.2866Z"/> <path d="M142.9466,49.108V44.2091h-1.24v-1.023h1.24V41.14h1.1626v2.0464h1.519v1.023h-1.519V48.86c0,.5581.248.9614.7592.9614a1.1239,1.1239,0,0,0,.7911-.31L146,50.38a1.9008,1.9008,0,0,1-1.395.48A1.5318,1.5318,0,0,1,142.9466,49.108Z"/> <path d="M151.3782,41.14a.7827.7827,0,0,1,1.5654,0,.7827.7827,0,1,1-1.5654,0Zm.2012,9.5342V43.1861h1.1631v7.4878Z"/> <path d="M160.2762,50.6739V45.775c0-1.3179-.6666-1.7363-1.6744-1.7363a2.89,2.89,0,0,0-2.2168,1.1626v5.4726h-1.163V43.1861h1.163v1.085A3.7126,3.7126,0,0,1,159.0511,43a2.1281,2.1281,0,0,1,2.3876,2.4184v5.2554Z"/> <path d="M164.15,49.108V44.2091h-1.24v-1.023h1.24V41.14h1.1631v2.0464h1.519v1.023h-1.519V48.86c0,.5581.248.9614.76.9614a1.1235,1.1235,0,0,0,.7906-.31l.3408.8682a1.9006,1.9006,0,0,1-1.395.48A1.5324,1.5324,0,0,1,164.15,49.108Z"/> <path d="M168.1951,46.9222a3.7113,3.7113,0,1,1,7.4106,0,3.7122,3.7122,0,1,1-7.4106,0Zm6.186,0a2.5153,2.5153,0,1,0-4.9765,0,2.62,2.62,0,0,0,2.4961,2.8992C173.4973,49.8214,174.3811,48.4571,174.3811,46.9222Z"/> <path d="M181.7576,48.8446a3.3932,3.3932,0,0,0,2.4648,1.07c1.1475,0,1.7676-.5115,1.7676-1.24,0-.8215-.9145-1.0849-1.9223-1.333-1.2715-.2947-2.7129-.6357-2.7129-2.186,0-1.1626,1.0073-2.1548,2.79-2.1548a3.79,3.79,0,0,1,2.7754,1.085l-.543.8061a2.9163,2.9163,0,0,0-2.2324-.9456c-1.0229,0-1.6587.4651-1.6587,1.1316,0,.7288.853.9615,1.83,1.1939,1.3022.2944,2.8057.6665,2.8057,2.3254,0,1.2556-1.0074,2.2635-2.9453,2.2635a3.9822,3.9822,0,0,1-3.023-1.1783Z"/> <path d="M192.4685,43a3.2056,3.2056,0,0,1,2.7442,1.3022l-.7754.7129a2.22,2.22,0,0,0-1.9068-.9765,2.6088,2.6088,0,0,0-2.5888,2.8835,2.6222,2.6222,0,0,0,2.5888,2.8992,2.2573,2.2573,0,0,0,1.9068-.9768l.7754.7131a3.2057,3.2057,0,0,1-2.7442,1.3023,3.935,3.935,0,0,1,0-7.86Z"/> <path d="M196.7923,41.14a.783.783,0,0,1,1.5659,0,.783.783,0,1,1-1.5659,0Zm.2016,9.5342V43.1861h1.1626v7.4878Z"/> <path d="M203.8919,43c2.2632,0,3.5967,1.7671,3.5967,4.0151V47.31H201.427a2.6382,2.6382,0,0,0,2.6973,2.5891,3.2746,3.2746,0,0,0,2.31-.9456l.5581.7595a4.0678,4.0678,0,0,1-2.9766,1.1473,3.9347,3.9347,0,0,1-.124-7.86Zm-2.4649,3.457h4.9141a2.4274,2.4274,0,0,0-2.4649-2.4961A2.4979,2.4979,0,0,0,201.427,46.4571Z"/> <path d="M214.5716,50.6739V45.775c0-1.3179-.667-1.7363-1.6744-1.7363a2.8928,2.8928,0,0,0-2.2172,1.1626v5.4726h-1.1626V43.1861H210.68v1.085A3.7155,3.7155,0,0,1,213.347,43a2.1281,2.1281,0,0,1,2.3872,2.4184v5.2554Z"/> <path d="M221.5149,43a3.2056,3.2056,0,0,1,2.7442,1.3022l-.7754.7129a2.22,2.22,0,0,0-1.9068-.9765,2.6088,2.6088,0,0,0-2.5888,2.8835,2.6222,2.6222,0,0,0,2.5888,2.8992,2.258,2.258,0,0,0,1.9068-.9768l.7754.7131a3.2057,3.2057,0,0,1-2.7442,1.3023,3.935,3.935,0,0,1,0-7.86Z"/> <path d="M229.2962,43c2.2632,0,3.5967,1.7671,3.5967,4.0151V47.31h-6.0616a2.6382,2.6382,0,0,0,2.6973,2.5891,3.2746,3.2746,0,0,0,2.31-.9456l.5581.7595A4.0678,4.0678,0,0,1,229.42,50.86a3.9347,3.9347,0,0,1-.124-7.86Zm-2.4649,3.457h4.9141a2.4274,2.4274,0,0,0-2.4649-2.4961A2.4979,2.4979,0,0,0,226.8313,46.4571Z"/> </g> </svg> </a> </div> <nav class="vl-header__menu"> <ul> <li class="library"> <a href="en/library/" aria-current=page > <span class="title">Library</span> <span class="tagline">Learning modules</span> </a> </li> <li class="glossary"> <a href="/en/glossary/" > <span class="title">Glossary</span> <span class="tagline">Science terms</span> </a> </li> <li class="classroom"> <a href="/en/classroom" > <span class="title">Classroom</span> <span class="tagline">Custom courses</span> </a> </li> </ul> </nav> </div> </header> <div class="wrap-viewport-height">  <nav class="module-breadcrumb border-bottom display-none display-block--md"> <ul class="wide margin-x-auto"> <li> <a class="button button--icon-only" href="/en/"> <span class="icon icon-home" aria-hidden="true"></span> </a> </li> <li> <button class="button" data-toggle="dropdown">Library</button> <div class="nav__dropdown box-shadow-1"> <div class="accordion accordion--secondary">  <button class="accordion__button" id="acc-button-biology" data-accordion="button" aria-controls="acc-panel-biology" aria-expanded="false"> <span class="accordion__button__label"> Biology </span> </button> <div class="accordion__panel" id="acc-panel-biology" data-accordion="panel" aria-labelledby="acc-button-biology" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-biological-molecules" data-accordion="button" aria-controls="acc-panel-biological-molecules" aria-expanded="false"> <span class="accordion__button__label"> Biological Molecules </span> </button> <div class="accordion__panel" id="acc-panel-biological-molecules" data-accordion="panel" aria-labelledby="acc-button-biological-molecules" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/carbohydrates/61">Carbohydrates</a></li> <li><a href="/en/library/biology/2/fats-and-proteins/62">Fats and Proteins</a></li> <li><a href="/en/library/biology/2/biological-proteins/243">Biological Proteins</a></li> <li><a href="/en/library/biology/2/blood-biology-i/242">Blood Biology I</a></li> <li class="current">Lipids</li> </ul> </div> <button class="accordion__button" id="acc-button-cell-biology" data-accordion="button" aria-controls="acc-panel-cell-biology" aria-expanded="false"> <span class="accordion__button__label"> Cell Biology </span> </button> <div class="accordion__panel" id="acc-panel-cell-biology" data-accordion="panel" aria-labelledby="acc-button-cell-biology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/discovery-and-structure-of-cells/64">Discovery and Structure of Cells</a></li> <li><a href="/en/library/biology/2/respiration/285">Respiration</a></li> <li><a href="/en/library/biology/2/membranes-i/198">Membranes I</a></li> <li><a href="/en/library/biology/2/membranes-ii/204">Membranes II</a></li> <li><a href="/en/library/biology/2/cellular-organelles-i/195">Cellular Organelles I</a></li> <li><a href="/en/library/biology/2/cell-division-i/196">Cell Division I</a></li> <li><a href="/en/library/biology/2/cell-division-ii/212">Cell Division II</a></li> <li><a href="/en/library/biology/2/membranes-and-chemical-transport/106">Membranes and Chemical Transport</a></li> </ul> </div> <button class="accordion__button" id="acc-button-energy-in-living-systems" data-accordion="button" aria-controls="acc-panel-energy-in-living-systems" aria-expanded="false"> <span class="accordion__button__label"> Energy in Living Systems </span> </button> <div class="accordion__panel" id="acc-panel-energy-in-living-systems" data-accordion="panel" aria-labelledby="acc-button-energy-in-living-systems" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/energy-metabolism-i/215">Energy Metabolism I</a></li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225">Energy Metabolism II</a></li> <li><a href="/en/library/biology/2/photosynthesis-i/192">Photosynthesis I</a></li> </ul> </div> <button class="accordion__button" id="acc-button-evolutionary-biology" data-accordion="button" aria-controls="acc-panel-evolutionary-biology" aria-expanded="false"> <span class="accordion__button__label"> Evolutionary Biology </span> </button> <div class="accordion__panel" id="acc-panel-evolutionary-biology" data-accordion="panel" aria-labelledby="acc-button-evolutionary-biology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/origins-of-life-i/226">Origins of Life I</a></li> <li><a href="/en/library/biology/2/origins-of-life-ii/227">Origins of Life II</a></li> <li><a href="/en/library/biology/2/extinction/295">Extinction</a></li> <li><a href="/en/library/biology/2/paleontology-and-the-fossil-record/301">Paleontology and the Fossil Record</a></li> <li><a href="/en/library/biology/2/mass-extinctions/294">Mass Extinctions</a></li> <li><a href="/en/library/biology/2/charles-darwin-i/110">Charles Darwin I</a></li> <li><a href="/en/library/biology/2/charles-darwin-ii/111">Charles Darwin II</a></li> <li><a href="/en/library/biology/2/charles-darwin-iii/112">Charles Darwin III</a></li> <li><a href="/en/library/biology/2/adaptation/68">Adaptation</a></li> <li><a href="/en/library/biology/2/taxonomy-i/70">Taxonomy I</a></li> <li><a href="/en/library/biology/2/taxonomy-ii/89">Taxonomy II</a></li> <li><a href="/en/library/biology/2/introduction-to-paleoanthropology/258">Introduction to Paleoanthropology</a></li> <li><a href="/en/library/biology/2/the-piltdown-hoax/263">The Piltdown Hoax</a></li> <li><a href="/en/library/biology/2/future-of-human-evolution/259">Future of Human Evolution</a></li> </ul> </div> <button class="accordion__button" id="acc-button-genetics" data-accordion="button" aria-controls="acc-panel-genetics" aria-expanded="false"> <span class="accordion__button__label"> Genetics </span> </button> <div class="accordion__panel" id="acc-panel-genetics" data-accordion="panel" aria-labelledby="acc-button-genetics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/inheritance/129">Inheritance</a></li> <li><a href="/en/library/biology/2/independent-assortment/145">Independent Assortment</a></li> <li><a href="/en/library/biology/2/dna-i/149">DNA I</a></li> <li><a href="/en/library/biology/2/dna-ii/160">DNA II</a></li> <li><a href="/en/library/biology/2/dna-iii/180">DNA III</a></li> <li><a href="/en/library/biology/2/tracking-human-ancestry/248">Tracking Human Ancestry</a></li> <li><a href="/en/library/biology/2/gene-expression/214">Gene Expression</a></li> <li><a href="/en/library/biology/2/population-genetics/249">Population Genetics</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ecology" data-accordion="button" aria-controls="acc-panel-ecology" aria-expanded="false"> <span class="accordion__button__label"> Ecology </span> </button> <div class="accordion__panel" id="acc-panel-ecology" data-accordion="panel" aria-labelledby="acc-button-ecology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/biodiversity-i/276">Biodiversity I</a></li> <li><a href="/en/library/biology/2/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/biology/2/animal-ecology/283">Animal Ecology</a></li> <li><a href="/en/library/biology/2/biodiversity-ii/281">Biodiversity II</a></li> <li><a href="/en/library/biology/2/animal-behavior/286">Animal Behavior</a></li> <li><a href="/en/library/biology/2/population-biology/287">Population Biology</a></li> <li><a href="/en/library/biology/2/trophic-ecology/293">Trophic Ecology</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-chemistry" data-accordion="button" aria-controls="acc-panel-chemistry" aria-expanded="false"> <span class="accordion__button__label"> Chemistry </span> </button> <div class="accordion__panel" id="acc-panel-chemistry" data-accordion="panel" aria-labelledby="acc-button-chemistry" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-atomic-theory-and-structure" data-accordion="button" aria-controls="acc-panel-atomic-theory-and-structure" aria-expanded="false"> <span class="accordion__button__label"> Atomic Theory and Structure </span> </button> <div class="accordion__panel" id="acc-panel-atomic-theory-and-structure" data-accordion="panel" aria-labelledby="acc-button-atomic-theory-and-structure" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/early-ideas-about-matter/49">Early Ideas about Matter</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-i/52">The Periodic Table of Elements I</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-ii/296">The Periodic Table of Elements II</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-iii/297">The Periodic Table of Elements III</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-iv/298">The Periodic Table of Elements IV</a></li> <li><a href="/en/library/chemistry/1/the-periodic-table-of-elements-v/299">The Periodic Table of Elements V</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-i/50">Atomic Theory I</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-ii/51">Atomic Theory II</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-iii/223">Atomic Theory III</a></li> <li><a href="/en/library/chemistry/1/atomic-theory-iv/231">Atomic Theory IV</a></li> <li><a href="/en/library/chemistry/1/the-mole-and-atomic-mass/53">The Mole and Atomic Mass</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-states-and-properties" data-accordion="button" aria-controls="acc-panel-physical-states-and-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical States and Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-states-and-properties" data-accordion="panel" aria-labelledby="acc-button-physical-states-and-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/states-of-matter/120">States of Matter</a></li> <li><a href="/en/library/chemistry/1/substances/280">Substances</a></li> <li><a href="/en/library/chemistry/1/properties-of-solids/209">Properties of Solids</a></li> <li><a href="/en/library/chemistry/1/properties-of-liquids/222">Properties of Liquids</a></li> <li><a href="/en/library/chemistry/1/properties-of-gases/245">Properties of Gases</a></li> <li><a href="/en/library/chemistry/1/diffusion-i/216">Diffusion I</a></li> <li><a href="/en/library/chemistry/1/kinetic-molecular-theory/251">Kinetic-Molecular Theory</a></li> <li><a href="/en/library/chemistry/1/solutions/266">Solutions</a></li> <li><a href="/en/library/chemistry/1/water/267">Water</a></li> </ul> </div> <button class="accordion__button" id="acc-button-chemical-relationships" data-accordion="button" aria-controls="acc-panel-chemical-relationships" aria-expanded="false"> <span class="accordion__button__label"> Chemical Relationships </span> </button> <div class="accordion__panel" id="acc-panel-chemical-relationships" data-accordion="panel" aria-labelledby="acc-button-chemical-relationships" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/chemical-bonding/55">Chemical Bonding</a></li> <li><a href="/en/library/chemistry/1/stoichiometry/270">Stoichiometry</a></li> <li><a href="/en/library/chemistry/1/chemical-equations/268">Chemical Equations</a></li> <li><a href="/en/library/chemistry/1/acids-and-bases-i/271">Acids and Bases I</a></li> <li><a href="/en/library/chemistry/1/acids-and-bases-ii/272">Acids and Bases II</a></li> </ul> </div> <button class="accordion__button" id="acc-button-reactions-and-changes" data-accordion="button" aria-controls="acc-panel-reactions-and-changes" aria-expanded="false"> <span class="accordion__button__label"> Reactions and Changes </span> </button> <div class="accordion__panel" id="acc-panel-reactions-and-changes" data-accordion="panel" aria-labelledby="acc-button-reactions-and-changes" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/chemistry/1/chemical-reactions/54">Chemical Reactions</a></li> <li><a href="/en/library/chemistry/1/chemical-reactions-ii/278">Chemical Reactions II</a></li> <li><a href="/en/library/chemistry/1/nuclear-chemistry-i/284">Nuclear Chemistry I</a></li> <li><a href="/en/library/chemistry/1/carbon-chemistry/60">Carbon Chemistry</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-earth-science" data-accordion="button" aria-controls="acc-panel-earth-science" aria-expanded="false"> <span class="accordion__button__label"> Earth Science </span> </button> <div class="accordion__panel" id="acc-panel-earth-science" data-accordion="panel" aria-labelledby="acc-button-earth-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-plate-tectonics" data-accordion="button" aria-controls="acc-panel-plate-tectonics" aria-expanded="false"> <span class="accordion__button__label"> Plate Tectonics </span> </button> <div class="accordion__panel" id="acc-panel-plate-tectonics" data-accordion="panel" aria-labelledby="acc-button-plate-tectonics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/origins-of-plate-tectonic-theory/65">Origins of Plate Tectonic Theory</a></li> <li><a href="/en/library/earth-science/6/plate-boundaries/66">Plate Boundaries</a></li> <li><a href="/en/library/earth-science/6/earth-structure/69">Earth Structure</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-cycles" data-accordion="button" aria-controls="acc-panel-earth-cycles" aria-expanded="false"> <span class="accordion__button__label"> Earth Cycles </span> </button> <div class="accordion__panel" id="acc-panel-earth-cycles" data-accordion="panel" aria-labelledby="acc-button-earth-cycles" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/the-rock-cycle/128">The Rock Cycle</a></li> <li><a href="/en/library/earth-science/6/the-hydrologic-cycle/99">The Hydrologic Cycle</a></li> <li><a href="/en/library/earth-science/6/the-carbon-cycle/95">The Carbon Cycle</a></li> <li><a href="/en/library/earth-science/6/the-nitrogen-cycle/98">The Nitrogen Cycle</a></li> <li><a href="/en/library/earth-science/6/the-phosphorus-cycle/197">The Phosphorus Cycle</a></li> </ul> </div> <button class="accordion__button" id="acc-button-rocks-and-minerals" data-accordion="button" aria-controls="acc-panel-rocks-and-minerals" aria-expanded="false"> <span class="accordion__button__label"> Rocks and Minerals </span> </button> <div class="accordion__panel" id="acc-panel-rocks-and-minerals" data-accordion="panel" aria-labelledby="acc-button-rocks-and-minerals" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/defining-minerals/119">Defining Minerals</a></li> <li><a href="/en/library/earth-science/6/identifying-minerals/130">Identifying Minerals</a></li> <li><a href="/en/library/earth-science/6/the-silicate-minerals/140">The Silicate Minerals</a></li> </ul> </div> <button class="accordion__button" id="acc-button-atmosphere-and-oceans" data-accordion="button" aria-controls="acc-panel-atmosphere-and-oceans" aria-expanded="false"> <span class="accordion__button__label"> Atmosphere and Oceans </span> </button> <div class="accordion__panel" id="acc-panel-atmosphere-and-oceans" data-accordion="panel" aria-labelledby="acc-button-atmosphere-and-oceans" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/ocean-currents/282">Ocean Currents</a></li> <li><a href="/en/library/earth-science/6/water-in-the-atmosphere/289">Water in the Atmosphere</a></li> <li><a href="/en/library/earth-science/6/weather-fronts-and-forecasts/303">Weather, Fronts, and Forecasts</a></li> <li><a href="/en/library/earth-science/6/history-of-earths-atmosphere-i/202">History of Earth's Atmosphere I</a></li> <li><a href="/en/library/earth-science/6/history-of-earths-atmosphere-ii/203">History of Earth's Atmosphere II</a></li> <li><a href="/en/library/earth-science/6/earths-atmosphere/107">Earth's Atmosphere</a></li> <li><a href="/en/library/earth-science/6/factors-that-control-earths-temperature/234">Factors that Control Earth's Temperature</a></li> <li><a href="/en/library/earth-science/6/circulation-in-the-atmosphere/255">Circulation in the Atmosphere</a></li> </ul> </div> <button class="accordion__button" id="acc-button-hazards" data-accordion="button" aria-controls="acc-panel-hazards" aria-expanded="false"> <span class="accordion__button__label"> Hazards </span> </button> <div class="accordion__panel" id="acc-panel-hazards" data-accordion="panel" aria-labelledby="acc-button-hazards" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/natural-hazards-and-risk/288">Natural Hazards and Risk</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-history" data-accordion="button" aria-controls="acc-panel-earth-history" aria-expanded="false"> <span class="accordion__button__label"> Earth History </span> </button> <div class="accordion__panel" id="acc-panel-earth-history" data-accordion="panel" aria-labelledby="acc-button-earth-history" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/extinction/295">Extinction</a></li> <li><a href="/en/library/earth-science/6/paleontology-and-the-fossil-record/301">Paleontology and the Fossil Record</a></li> <li><a href="/en/library/earth-science/6/mass-extinctions/294">Mass Extinctions</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-environmental-science" data-accordion="button" aria-controls="acc-panel-environmental-science" aria-expanded="false"> <span class="accordion__button__label"> Environmental Science </span> </button> <div class="accordion__panel" id="acc-panel-environmental-science" data-accordion="panel" aria-labelledby="acc-button-environmental-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-ecology" data-accordion="button" aria-controls="acc-panel-ecology" aria-expanded="false"> <span class="accordion__button__label"> Ecology </span> </button> <div class="accordion__panel" id="acc-panel-ecology" data-accordion="panel" aria-labelledby="acc-button-ecology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/biodiversity-i/276">Biodiversity I</a></li> <li><a href="/en/library/environmental-science/61/biodiversity-ii/281">Biodiversity II</a></li> <li><a href="/en/library/environmental-science/61/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/environmental-science/61/population-biology/287">Population Biology</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-cycles" data-accordion="button" aria-controls="acc-panel-earth-cycles" aria-expanded="false"> <span class="accordion__button__label"> Earth Cycles </span> </button> <div class="accordion__panel" id="acc-panel-earth-cycles" data-accordion="panel" aria-labelledby="acc-button-earth-cycles" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/the-nitrogen-cycle/98">The Nitrogen Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-carbon-cycle/95">The Carbon Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-phosphorus-cycle/197">The Phosphorus Cycle</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/environmental-science/61/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-general-science" data-accordion="button" aria-controls="acc-panel-general-science" aria-expanded="false"> <span class="accordion__button__label"> General Science </span> </button> <div class="accordion__panel" id="acc-panel-general-science" data-accordion="panel" aria-labelledby="acc-button-general-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-methods" data-accordion="button" aria-controls="acc-panel-methods" aria-expanded="false"> <span class="accordion__button__label"> Methods </span> </button> <div class="accordion__panel" id="acc-panel-methods" data-accordion="panel" aria-labelledby="acc-button-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-scientific-method/45">The Scientific Method</a></li> </ul> </div> <button class="accordion__button" id="acc-button-measurement" data-accordion="button" aria-controls="acc-panel-measurement" aria-expanded="false"> <span class="accordion__button__label"> Measurement </span> </button> <div class="accordion__panel" id="acc-panel-measurement" data-accordion="panel" aria-labelledby="acc-button-measurement" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-metric-system/47">The Metric System</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-properties" data-accordion="button" aria-controls="acc-panel-physical-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-properties" data-accordion="panel" aria-labelledby="acc-button-physical-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/temperature/48">Temperature</a></li> <li><a href="/en/library/general-science/3/density-and-buoyancy/37">Density and Buoyancy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-math-in-science" data-accordion="button" aria-controls="acc-panel-math-in-science" aria-expanded="false"> <span class="accordion__button__label"> Math in Science </span> </button> <div class="accordion__panel" id="acc-panel-math-in-science" data-accordion="panel" aria-labelledby="acc-button-math-in-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-equations" data-accordion="button" aria-controls="acc-panel-equations" aria-expanded="false"> <span class="accordion__button__label"> Equations </span> </button> <div class="accordion__panel" id="acc-panel-equations" data-accordion="panel" aria-labelledby="acc-button-equations" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/unit-conversion/144">Unit Conversion</a></li> <li><a href="/en/library/math-in-science/62/linear-equations/194">Linear Equations</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-i/206">Exponential Equations I</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-ii/210">Exponential Equations II</a></li> <li><a href="/en/library/math-in-science/62/scientific-notation/250">Scientific Notation</a></li> <li><a href="/en/library/math-in-science/62/measurement/257">Measurement</a></li> </ul> </div> <button class="accordion__button" id="acc-button-statistics" data-accordion="button" aria-controls="acc-panel-statistics" aria-expanded="false"> <span class="accordion__button__label"> Statistics </span> </button> <div class="accordion__panel" id="acc-panel-statistics" data-accordion="panel" aria-labelledby="acc-button-statistics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/introduction-to-descriptive-statistics/218">Introduction to Descriptive Statistics</a></li> <li><a href="/en/library/math-in-science/62/introduction-to-inferential-statistics/224">Introduction to Inferential Statistics</a></li> <li><a href="/en/library/math-in-science/62/statistical-techniques/239">Statistical Techniques</a></li> </ul> </div> <button class="accordion__button" id="acc-button-trigonometric-functions" data-accordion="button" aria-controls="acc-panel-trigonometric-functions" aria-expanded="false"> <span class="accordion__button__label"> Trigonometric Functions </span> </button> <div class="accordion__panel" id="acc-panel-trigonometric-functions" data-accordion="panel" aria-labelledby="acc-button-trigonometric-functions" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/wave-mathematics/131">Wave Mathematics</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-physics" data-accordion="button" aria-controls="acc-panel-physics" aria-expanded="false"> <span class="accordion__button__label"> Physics </span> </button> <div class="accordion__panel" id="acc-panel-physics" data-accordion="panel" aria-labelledby="acc-button-physics" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-light-and-optics" data-accordion="button" aria-controls="acc-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/the-nature-of-light/132">The Nature of Light</a></li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-button-mechanics" data-accordion="button" aria-controls="acc-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-panel-mechanics" data-accordion="panel" aria-labelledby="acc-button-mechanics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/defining-energy/199">Defining Energy</a></li> <li><a href="/en/library/physics/24/waves-and-wave-motion/102">Waves and Wave Motion</a></li> <li><a href="/en/library/physics/24/gravity/118">Gravity</a></li> <li><a href="/en/library/physics/24/thermodynamics-i/200">Thermodynamics I</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-process-of-science" data-accordion="button" aria-controls="acc-panel-process-of-science" aria-expanded="false"> <span class="accordion__button__label"> Process of Science </span> </button> <div class="accordion__panel" id="acc-panel-process-of-science" data-accordion="panel" aria-labelledby="acc-button-process-of-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-introduction" data-accordion="button" aria-controls="acc-panel-introduction" aria-expanded="false"> <span class="accordion__button__label"> Introduction </span> </button> <div class="accordion__panel" id="acc-panel-introduction" data-accordion="panel" aria-labelledby="acc-button-introduction" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-process-of-science/176">The Process of Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-the-culture-of-science" data-accordion="button" aria-controls="acc-panel-the-culture-of-science" aria-expanded="false"> <span class="accordion__button__label"> The Culture of Science </span> </button> <div class="accordion__panel" id="acc-panel-the-culture-of-science" data-accordion="panel" aria-labelledby="acc-button-the-culture-of-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-nature-of-scientific-knowledge/185">The Nature of Scientific Knowledge</a></li> <li><a href="/en/library/process-of-science/49/scientists-and-the-scientific-community/172">Scientists and the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ideas-in-science" data-accordion="button" aria-controls="acc-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177">Theories, Hypotheses, and Laws</a></li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-research-methods" data-accordion="button" aria-controls="acc-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-panel-research-methods" data-accordion="panel" aria-labelledby="acc-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/modeling-in-scientific-research/153">Modeling in Scientific Research</a></li> </ul> </div> <button class="accordion__button" id="acc-button-data" data-accordion="button" aria-controls="acc-panel-data" aria-expanded="false"> <span class="accordion__button__label"> Data </span> </button> <div class="accordion__panel" id="acc-panel-data" data-accordion="panel" aria-labelledby="acc-button-data" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/data-analysis-and-interpretation/154">Data Analysis and Interpretation</a></li> <li><a href="/en/library/process-of-science/49/uncertainty-error-and-confidence/157">Uncertainty, Error, and Confidence</a></li> <li><a href="/en/library/process-of-science/49/statistics-in-science/155">Statistics in Science</a></li> <li><a href="/en/library/process-of-science/49/using-graphs-and-visual-data-in-science/156">Using Graphs and Visual Data in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-communication" data-accordion="button" aria-controls="acc-panel-scientific-communication" aria-expanded="false"> <span class="accordion__button__label"> Scientific Communication </span> </button> <div class="accordion__panel" id="acc-panel-scientific-communication" data-accordion="panel" aria-labelledby="acc-button-scientific-communication" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/understanding-scientific-journals-and-articles/158">Understanding Scientific Journals and Articles</a></li> <li><a href="/en/library/process-of-science/49/utilizing-the-scientific-literature/173">Utilizing the Scientific Literature</a></li> <li><a href="/en/library/process-of-science/49/peer-review-in-scientific-publishing/159">Peer Review in Scientific Publishing</a></li> <li><a href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-scientists-and-research" data-accordion="button" aria-controls="acc-panel-scientists-and-research" aria-expanded="false"> <span class="accordion__button__label"> Scientists and Research </span> </button> <div class="accordion__panel" id="acc-panel-scientists-and-research" data-accordion="panel" aria-labelledby="acc-button-scientists-and-research" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187">An Elegant Experiment to Test the Process of DNA Replication</a></li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-button-profiles-in-science" data-accordion="button" aria-controls="acc-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-díaz/219">Franklin Chang Díaz</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-córdova/230">France Anne-Dominic Córdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Biology </button> <div class="nav__dropdown box-shadow-1 padding-1"> <div class="accordion accordion--secondary font-size-sm"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-sub-button-biological-molecules" data-accordion="button" aria-controls="acc-sub-panel-biological-molecules" aria-expanded="false"> <span class="accordion__button__label"> Biological Molecules </span> </button> <div class="accordion__panel" id="acc-sub-panel-biological-molecules" data-accordion="panel" aria-labelledby="acc-sub-button-biological-molecules" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/carbohydrates/61">Carbohydrates</a></li> <li><a href="/en/library/biology/2/fats-and-proteins/62">Fats and Proteins</a></li> <li><a href="/en/library/biology/2/biological-proteins/243">Biological Proteins</a></li> <li><a href="/en/library/biology/2/blood-biology-i/242">Blood Biology I</a></li> <li class="current">Lipids</li> </ul> </div> <button class="accordion__button" id="acc-sub-button-cell-biology" data-accordion="button" aria-controls="acc-sub-panel-cell-biology" aria-expanded="false"> <span class="accordion__button__label"> Cell Biology </span> </button> <div class="accordion__panel" id="acc-sub-panel-cell-biology" data-accordion="panel" aria-labelledby="acc-sub-button-cell-biology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/discovery-and-structure-of-cells/64">Discovery and Structure of Cells</a></li> <li><a href="/en/library/biology/2/respiration/285">Respiration</a></li> <li><a href="/en/library/biology/2/membranes-i/198">Membranes I</a></li> <li><a href="/en/library/biology/2/membranes-ii/204">Membranes II</a></li> <li><a href="/en/library/biology/2/cellular-organelles-i/195">Cellular Organelles I</a></li> <li><a href="/en/library/biology/2/cell-division-i/196">Cell Division I</a></li> <li><a href="/en/library/biology/2/cell-division-ii/212">Cell Division II</a></li> <li><a href="/en/library/biology/2/membranes-and-chemical-transport/106">Membranes and Chemical Transport</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-energy-in-living-systems" data-accordion="button" aria-controls="acc-sub-panel-energy-in-living-systems" aria-expanded="false"> <span class="accordion__button__label"> Energy in Living Systems </span> </button> <div class="accordion__panel" id="acc-sub-panel-energy-in-living-systems" data-accordion="panel" aria-labelledby="acc-sub-button-energy-in-living-systems" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/energy-metabolism-i/215">Energy Metabolism I</a></li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225">Energy Metabolism II</a></li> <li><a href="/en/library/biology/2/photosynthesis-i/192">Photosynthesis I</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-evolutionary-biology" data-accordion="button" aria-controls="acc-sub-panel-evolutionary-biology" aria-expanded="false"> <span class="accordion__button__label"> Evolutionary Biology </span> </button> <div class="accordion__panel" id="acc-sub-panel-evolutionary-biology" data-accordion="panel" aria-labelledby="acc-sub-button-evolutionary-biology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/origins-of-life-i/226">Origins of Life I</a></li> <li><a href="/en/library/biology/2/origins-of-life-ii/227">Origins of Life II</a></li> <li><a href="/en/library/biology/2/extinction/295">Extinction</a></li> <li><a href="/en/library/biology/2/paleontology-and-the-fossil-record/301">Paleontology and the Fossil Record</a></li> <li><a href="/en/library/biology/2/mass-extinctions/294">Mass Extinctions</a></li> <li><a href="/en/library/biology/2/charles-darwin-i/110">Charles Darwin I</a></li> <li><a href="/en/library/biology/2/charles-darwin-ii/111">Charles Darwin II</a></li> <li><a href="/en/library/biology/2/charles-darwin-iii/112">Charles Darwin III</a></li> <li><a href="/en/library/biology/2/adaptation/68">Adaptation</a></li> <li><a href="/en/library/biology/2/taxonomy-i/70">Taxonomy I</a></li> <li><a href="/en/library/biology/2/taxonomy-ii/89">Taxonomy II</a></li> <li><a href="/en/library/biology/2/introduction-to-paleoanthropology/258">Introduction to Paleoanthropology</a></li> <li><a href="/en/library/biology/2/the-piltdown-hoax/263">The Piltdown Hoax</a></li> <li><a href="/en/library/biology/2/future-of-human-evolution/259">Future of Human Evolution</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-genetics" data-accordion="button" aria-controls="acc-sub-panel-genetics" aria-expanded="false"> <span class="accordion__button__label"> Genetics </span> </button> <div class="accordion__panel" id="acc-sub-panel-genetics" data-accordion="panel" aria-labelledby="acc-sub-button-genetics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/inheritance/129">Inheritance</a></li> <li><a href="/en/library/biology/2/independent-assortment/145">Independent Assortment</a></li> <li><a href="/en/library/biology/2/dna-i/149">DNA I</a></li> <li><a href="/en/library/biology/2/dna-ii/160">DNA II</a></li> <li><a href="/en/library/biology/2/dna-iii/180">DNA III</a></li> <li><a href="/en/library/biology/2/tracking-human-ancestry/248">Tracking Human Ancestry</a></li> <li><a href="/en/library/biology/2/gene-expression/214">Gene Expression</a></li> <li><a href="/en/library/biology/2/population-genetics/249">Population Genetics</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-ecology" data-accordion="button" aria-controls="acc-sub-panel-ecology" aria-expanded="false"> <span class="accordion__button__label"> Ecology </span> </button> <div class="accordion__panel" id="acc-sub-panel-ecology" data-accordion="panel" aria-labelledby="acc-sub-button-ecology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/biodiversity-i/276">Biodiversity I</a></li> <li><a href="/en/library/biology/2/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/biology/2/animal-ecology/283">Animal Ecology</a></li> <li><a href="/en/library/biology/2/biodiversity-ii/281">Biodiversity II</a></li> <li><a href="/en/library/biology/2/animal-behavior/286">Animal Behavior</a></li> <li><a href="/en/library/biology/2/population-biology/287">Population Biology</a></li> <li><a href="/en/library/biology/2/trophic-ecology/293">Trophic Ecology</a></li> </ul> </div> </div> </div> </div> </li> </ul> </nav>  <div id="theTop"></div> <main id="skip-header-content"> <div class="margin-bottom-5"> <div class="container narrow wide--lg margin-y-4"> <article class="module"> <header class="module__header"> <span class="subcategory"> <strong><em>Biological Molecules</em></strong> </span> <h1>Lipids: <sub><em>Composition, structure, and function</em></sub></h1> <p class="byline">by Nathan H Lents, Ph.D., Lizzie Stark, M.S./M.F.A, Bonnie Denmark, M.A./M.S.</p> </header> <nav class="module__tabs"> <ul class="tabs-nav tabs-nav--pill tabs-nav--horizontal--md library"> <li> <a href="/en/library/biology/2/lipids/207/reading" class="is-active" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/biology/2/lipids/207/quiz" >Quiz</a> </li> <li> <a href="/en/library/biology/2/lipids/207/resources" >Teach with this</a> </li> </ul> </nav> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_207.mp3", "description": "Recording of Lipids : Fats, oils, waxes, steroids, certain plant pigments, and parts of the cell membrane – these are all lipids. This module explores the world of lipids, a class of compounds produced by both plants and animals. It begins with a look at the chemical reaction that produces soap and then examines the chemical composition of a wide variety of lipid types. Properties and functions of lipids are discussed.", "encodingFormat": "mp3", "name": "module_207.mp3" } </script> <div class="module__audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_207.mp3" type="audio/mpeg"> Your browser does not support the audio element. </audio> <div class="audio-player__title"> <p>Listen to this reading</p> <span class="audio-player__timestamp" id="timestamp"> 00:00 </span> </div> <div class="audio-player__controls" id="controls"> <button class="button button--icon-only" id="play-pause-button"> <span class="icon icon-play" aria-hidden="true"></span> </button> <div class="audio-player__progress" id="progress-bar" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-label="Use arrow keys to forward or rewind the audio" role="slider"> <div class="audio-player__progress__fill"> <span class="audio-player__thumb"></span> </div> </div> <div class="audio-player__volume-container"> <button id="mute-button"> <span class="icon icon-volume"></span> </button> <div class="audio-player__volume" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" aria-label="Use arrow keys to adjust volume" role="slider"> <div class="audio-player__volume__fill"> <span class="audio-player__thumb"></span> </div> </div> </div> </div> </div> </div> <hr class="module__divider" />  <div class="module__tools"> <aside class="module__tools__container border-radius box-shadow-1"> <div class="tabs tabs--toggle-mobile--lg" role="tablist"> <ul class="tab__buttons"> <li> <button class="button button--icon-over-text" aria-label="In this module" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="button__icon"> <span class="icon icon-list" aria-hidden="true"></span> </span> <span class="button__text">Contents</span> </button> </li> <li> <button class="button button--icon-over-text" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="button__icon"> <span class="icon icon-glossary-highlight"></span> </span> <span class="button__text">Glossary Terms</span> </button> </li> </ul> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <div class="table-of-contents"> <p class="table-of-contents__title"> Table of Contents </p> <ul class="table-of-contents__nav"> <li><a href="/en/library/biology/2/lipids/207#toc_1">What is a lipid?</a> </li> <li><a href="/en/library/biology/2/lipids/207#toc_2">Lipid compounds</a> </li> <li><a href="/en/library/biology/2/lipids/207#toc_3">The composition of lipids</a> </li> <li><a href="/en/library/biology/2/lipids/207#toc_4">The structure of fats</a> </li> <li><a href="/en/library/biology/2/lipids/207#toc_5">Fats and oils store energy</a> </li> <li> <ul> <li><a href="/en/library/biology/2/lipids/207#toc2_1">Structure of fatty acids</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/biology/2/lipids/207#toc2_2">Trans fats</a> </li> </ul> </li> <li><a href="/en/library/biology/2/lipids/207#toc_6">Phospholipids and glycolipids form cellular membranes</a> </li> <li><a href="/en/library/biology/2/lipids/207#toc_7">Steroids provide structure and cell signaling</a> </li> <li> <ul> <li><a href="/en/library/biology/2/lipids/207#toc2_3">Cholesterol</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/biology/2/lipids/207#toc2_4">Other steroids</a> </li> </ul> </li> <li><a href="/en/library/biology/2/lipids/207#toc_8">Other lipids</a> </li> <li> <ul> <li><a href="/en/library/biology/2/lipids/207#toc2_5">Carotenoids</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/biology/2/lipids/207#toc2_6">Waxes</a> </li> </ul> </li> <li><a href="/en/library/biology/2/lipids/207#toc_9">Lipid research and medical science</a> </li> </ul> </div> </div> <div class="tabs__panel" id="tab-panel-toggle-terms" aria-labelledby="tab-button-toggle-terms" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="termsToggleSwitch" id="terms-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Highlight Glossary Terms </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions. </em> </p> </div> </div> <div class="glossary-container"></div> </div> <div class="tabs__panel" id="tab-panel-toggle-ngss" aria-labelledby="tab-button-toggle-ngss" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="ngssToggleSwitch" id="ngss-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Show NGSS Annotations </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate NGSS annotations to easily identify NGSS standards within the module. Once highlighted, you can click on them to view these standards. </em> </p> </div> </div> <div class="ngss-container"></div> </div> </div> </aside> <div class="margin-3"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-9561344156007092" data-ad-slot="7634263342" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> </div>     <div class="module__main"> <div class="module__main__container"> <div class="accordion">  <button class="accordion__button" id="acc-button-key-concepts" data-accordion="button" aria-controls="acc-panel-key-concepts" aria-expanded="true" tabindex="0"> Did you know? </button> <div class="accordion__panel shown show" id="acc-panel-key-concepts" data-accordion="panel" aria-labelledby="acc-button-key-concepts" role="region"> <div class="accordion__panel__content"> <p>Did you know that studying lipids can help us understand and treat medical conditions such as heart disease, hormone disorders, multiple sclerosis, and many others? Lipids are necessary for the structure of all living cells. Their chemical composition allows them to have many important functions, from storing energy to regulating metabolism to helping the fur coat of sea otters repel water.</p> </div> </div>  <button class="accordion__button" id="acc-button-table-of-contents" data-accordion="button" aria-controls="acc-panel-table-of-contents" aria-expanded="false" tabindex="0"> Key concepts </button> <div class="accordion__panel" id="acc-panel-table-of-contents" data-accordion="panel" aria-labelledby="acc-button-table-of-contents" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <ul class="bulleted"> <li><p>Lipids are a large and diverse class of biological molecules marked by their being hydrophobic, or unable to dissolve in water.</p></li> <li><p>The hydrophobic nature of lipids stems from the many nonpolar covalent bonds. Water, on the other hand, has polar covalent bonds and mixes well only with other polar or charged compounds.</p></li> <li><p>Fats and oils are high-energy molecules used by organisms to store and transfer chemical energy. The distinct structures of different fat molecules gives them different properties.</p></li> <li><p>Phospholipids are specialized lipids that are partially soluble in water. This dual nature allows them to form structures called membranes which surround all living cells.</p></li> </ul> </div> </div>  <button class="accordion__button" id="acc-button-terms-you-should-know" data-accordion="button" aria-controls="acc-panel-terms-you-should-know" aria-expanded="false" tabindex="0"> Terms you should know </button> <div class="accordion__panel" id="acc-panel-terms-you-should-know" data-accordion="panel" aria-labelledby="acc-button-terms-you-should-know" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <dl> <dt><a href="/en/glossary/view/bonding">bonding </a></dt> <dd> the act of fastening two atoms together </dd> <dt><a href="/en/glossary/view/membrane">membrane </a></dt> <dd> layer of tissue that forms the boundary of a cell </dd> <dt><a href="/en/glossary/view/polar">polar </a></dt> <dd> carrying an electrical charge</dd> </dl> </div> </div> </div> <section> <p>What do butter, beeswax, and testosterone have in common? They’re all <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark>, a type of <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compound</mark> produced by plants and animals that includes fats and oils as well as waxes and steroids. As a group, lipids have many different functions and uses in living <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> and <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>, from storing <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> to regulating <mark class="term" data-term="metabolism" data-term-def="A sequence of biochemical reactions in living organisms that converts food into energy used to drive other biological processes. Also, the&hellip;" data-term-url="/en/glossary/view/metabolism/1606">metabolism</mark>, signaling <mark class="term" data-term="hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;" data-term-url="/en/glossary/view/hormone/10183">hormones</mark>, and providing the structure of cell <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark>. They help sea otters’ fur <mark class="term" data-term="repel" data-term-def="To drive away, to force back, to resist, to ward off." data-term-url="/en/glossary/view/repel/8531">repel</mark> water and give a waxy sheen to many plant leaves. In our daily lives, lipids provide the delicious richness in ice cream, give carrots their color, lubricate our car engines, and help clean our clothes.</p> <p><section id="toc_1" class=""> <h2>What <em>is</em> a lipid?</h2></p> <p>If you have ever made salad dressing, seen a photograph of an oil tanker spill, or tried to clean a greasy stain with water, then you have likely noticed one of the defining factors of lipids: They do not mix well with water. <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">Lipids</mark> are mainly composed of carbon and hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark>, and this <mark class="term" data-term="hydrophobic" data-term-def="Literally meaning "water fearing," a substance that has little affinity for water. Generally, non-polar molecules that do not dissolve in&hellip;" data-term-url="/en/glossary/view/hydrophobic/1600">hydrophobic</mark> ("water fearing") nature of lipids is driven by the <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> between these many carbons and hydrogens.</p><p>In a water <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark>, the <mark class="term" data-term="bonding" data-term-def="The act of fastening two atoms together." data-term-url="/en/glossary/view/bonding/8295">bonding</mark> between the oxygen and hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> results in a <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark> covalent <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bond</mark> (see our module <a href="/en/library/Chemistry/1/Water/57">Water: Properties and Behavior</a>). The <mark class="term" data-term="electron" data-term-def="A subatomic particle with a negative charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 9.11 × 10<sup>-31</sup> kg. Electrons&hellip;" data-term-url="/en/glossary/view/electron/852">electrons</mark> that form this bond are shared unequally between the atoms because oxygen atoms have a stronger pull on electrons than hydrogen does. This creates a slight negative <mark class="term" data-term="charge" data-term-def="A quantity of electricity." data-term-url="/en/glossary/view/charge/8258">charge</mark> at the oxygen end of the water molecule, and a slight positive charge at the hydrogen end, as shown in Figure 1.</p><div class="figure"><figure> <img src="https://www.visionlearning.com/images/figure-images/207-a.jpg" alt="Water molecule"> <figcaption><strong>Figure 1:</strong> Electronic distribution in H<sub>2</sub>O.</figcaption> </figure></div> <div class="container margin-y-4 text-align-center"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:inline-block;width:300px;height:250px" data-ad-client="ca-pub-9561344156007092" data-ad-slot="9090201191"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> <p>However, the <mark class="term" data-term="bonding" data-term-def="The act of fastening two atoms together." data-term-url="/en/glossary/view/bonding/8295">bonding</mark> between carbon and hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> in <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> is not <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark>. This is because the <mark class="term" data-term="electron" data-term-def="A subatomic particle with a negative charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 9.11 × 10<sup>-31</sup> kg. Electrons&hellip;" data-term-url="/en/glossary/view/electron/852">electrons</mark> in the covalent <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> are shared equally between the carbons and the hydrogens and there are no partial <mark class="term" data-term="charge" data-term-def="A quantity of electricity." data-term-url="/en/glossary/view/charge/8258">charges</mark> anywhere. Thus, long chains of carbon-hydrogens bonds form a nonpolar <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark>.</p><p>The <mark class="term" data-term="bonding" data-term-def="The act of fastening two atoms together." data-term-url="/en/glossary/view/bonding/8295">bonding</mark> differences between water and lipid <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> is important because “like attracts like.” As a <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark> <mark class="term" data-term="solvent" data-term-def="The most abundant component in a homogeneous mixture of two or more substances." data-term-url="/en/glossary/view/solvent/1565">solvent</mark>, water prefers to dissolve molecules with polar <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark>, such as <mark class="term" data-term="salt" data-term-def="Generally, any ionic compound except those that contain hydroxide or hydrogen ions. Specifically, any compound other than water formed by&hellip;" data-term-url="/en/glossary/view/salt/1575">salt</mark> and <mark class="term" data-term="sugar" data-term-def="A water-soluble crystalline carbohydrate. There are many types of sugar of varying degrees of sweetness, including fructose, which occurs naturally in&hellip;" data-term-url="/en/glossary/view/sugar/5309">sugar</mark>. Molecules with nonpolar bonds will not normally dissolve in polar solvents because there is no <mark class="term" data-term="charge" data-term-def="A quantity of electricity." data-term-url="/en/glossary/view/charge/8258">charge</mark> on the <mark class="term" data-term="nonpolar molecule" data-term-def="A molecule that has an equal distribution of bonding electrons across it and possesses no partial positive or negative charges. Nonpolar&hellip;" data-term-url="/en/glossary/view/nonpolar+molecule/1556">nonpolar molecule</mark> to attract the <mark class="term" data-term="polar molecule" data-term-def="Refer to polar covalent molecule." data-term-url="/en/glossary/view/polar+molecule/2568">polar molecule</mark>. Nonpolar <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquids</mark> mix with other nonpolar <mark class="term" data-term="liquid" data-term-url="/en/glossary/view/liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;">liquids</mark> and dissolve nonpolar <mark class="term" data-term="solute" data-term-def="A compound dissolved in a solvent to create a solution." data-term-url="/en/glossary/view/solute/8729">solutes</mark> (the substance that is dissolved); polar liquids mix with other polar liquids and dissolve polar or charged solutes.</p><p>While <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> cannot dissolve in <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark> <mark class="term" data-term="solvent" data-term-def="The most abundant component in a homogeneous mixture of two or more substances." data-term-url="/en/glossary/view/solvent/1565">solvents</mark>, they can dissolve in nonpolar solvents – those with a balanced <mark class="term" data-term="electron" data-term-def="A subatomic particle with a negative charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 9.11 × 10<sup>-31</sup> kg. Electrons&hellip;" data-term-url="/en/glossary/view/electron/852">electron</mark> distribution – such as gasoline and chloroform. This is why lighter <mark class="term" data-term="fluid" data-term-def="Able to flow because the intermolecular forces allow the molecules to move around in relation to one another. Both liquids and&hellip;" data-term-url="/en/glossary/view/fluid/8724">fluid</mark> can help remove engine grease and cooking oil stains from clothing. </p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7254"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Covalent bonds between atoms are polar when</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7254-0-option-a" name="quiz-option-7254" type="radio" value="electrons are shared unequally." > <span class="option__label"> <span class="screen-reader-only">a.</span> electrons are shared unequally. </span> </label> <span class="quiz__response" id="response-7254-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7254-1-option-b" name="quiz-option-7254" type="radio" value="a molecule comes into contact with water." > <span class="option__label"> <span class="screen-reader-only">b.</span> a molecule comes into contact with water. </span> </label> <span class="quiz__response" id="response-7254-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_2"> <h2>Lipid compounds</h2><p>As a group, <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> are a diverse collection of naturally-occurring <mark class="term" data-term="organic" data-term-def="Originating from a living organism; a compound that contains hydrocarbons." data-term-url="/en/glossary/view/organic/8530">organic</mark> <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compounds</mark> with important roles to play:</p><p><ul class="bulleted"> <li><strong>Fats and oils</strong> store <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> for <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>. In animals, they provide electrical insulation for nerves, and cushion internal organs.</li> <li><strong>Phospholipids</strong> form cellular <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> and play an important role in <mark class="term" data-term="diffusion" data-term-def="The movement of atoms or molecules from one part of a medium to another caused by their random thermal motion.&hellip;" data-term-url="/en/glossary/view/diffusion/2690">diffusion</mark> (see our <a href="/en/library/Biology/2/Membranes-I/198">Membranes I: Introduction to Biological Membranes</a> module).</li> <li><strong>Steroids</strong> are formed from cholesterol and are involved in cellular communication.</li> <li><strong>Carotenoids</strong> are <mark class="term" data-term="pigment" data-term-def="A light-absorbing molecule that gathers energy from the sun; a molecule that gives color and is involved in vital functions within&hellip;" data-term-url="/en/glossary/view/pigment/8522">pigments</mark> used to help <mark class="term" data-term="absorb" data-term-def="Take in or soak up (energy, liquids, or other substances), usually gradually, through a chemical or physical action." data-term-url="/en/glossary/view/absorb/11219">absorb</mark> <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> energy in plants, <mark class="term" data-term="algae" data-term-def="(plural form of <b>alga</b>) Mostly aquatic plantlike organisms that range in size from one cell to large multi-celled seaweed and are photosynthetic." data-term-url="/en/glossary/view/algae/8678">algae</mark>, and photosynthetic <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>.</li> <li><strong>Waxes</strong> form a barrier to exclude water in both plants and animals. Waxes are found in leaves, ear canals, and the beeswax that makes honeycomb.</li> </ul></p></section> <section id="toc_3"> <h2>The composition of lipids</h2><p>Without fully realizing it, humans have been performing <mark class="term" data-term="chemical reaction" data-term-def="A process in which atoms and molecules recombine by forming or breaking chemical bonds. Chemical reactions form new products that&hellip;" data-term-url="/en/glossary/view/chemical+reaction/1547">chemical reactions</mark> with <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> for thousands of years. Soap, for example, was a very early human invention and possibly the first such innovation to be the result of a chemical <mark class="term" data-term="reaction" data-term-def="A chemical change when substances come into contact with each other." data-term-url="/en/glossary/view/reaction/8263">reaction</mark>. There is even a recipe for making soap on Sumerian tablets dating back to 2500 <mark class="term" data-term="BCE" data-term-def="An abbreviation for Before the Common Era, which is a designation for the years prior to year 1 of the Gregorian&hellip;" data-term-url="/en/glossary/view/BCE/3720">BCE</mark> (Levey, 1954). In the ancient world, soap was made by first boiling rainwater with ashes from burnt wood to produce lye: a very basic, or alkaline, <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> (high pH) (see our <a href="/en/library/Chemistry/1/Acids-and-Bases/58">Acids and Bases: An Introduction</a> module). Next, this solution was combined with animal fat or vegetable oil and cooked over a low fire for many hours until the mixture changed into a gel. The fundamental procedure of this chemical reaction, now called <mark class="term" data-term="saponification" data-term-def="The process of converting a fat or an oil into soap through combination with an alkali." data-term-url="/en/glossary/view/saponification/7315">saponification</mark>, is still used today to make soap.</p><p>The first steps toward understanding <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> were taken in the early 1800s by a young French scientist named Michel Chevreul (1786-1889). Chevreul began his career in the laboratory of Louis Vauquelin, where his role was to use various <mark class="term" data-term="solvent" data-term-def="The most abundant component in a homogeneous mixture of two or more substances." data-term-url="/en/glossary/view/solvent/1565">solvents</mark> (such as water, <mark class="term" data-term="alcohol" data-term-def="An organic compound containing a hydroxyl group. Common examples include methanol (CH<sub>3</sub>OH) and ethanol (CH<sub>3</sub>CH<sub>2</sub>OH)." data-term-url="/en/glossary/view/alcohol/1592">alcohol</mark>, and ether) to separate the colored dye <mark class="term" data-term="pigment" data-term-def="A light-absorbing molecule that gathers energy from the sun; a molecule that gives color and is involved in vital functions within&hellip;" data-term-url="/en/glossary/view/pigment/8522">pigments</mark> from natural <mark class="term" data-term="product" data-term-def="The material that is formed as a result of a chemical reaction. Written on the right side of a chemical equation.&hellip;" data-term-url="/en/glossary/view/product/1569">products</mark> like vegetable oils, waxes, tree gums, and resins. Without knowing it, he was working with various kinds of lipids (McNamara, Warnick, & Cooper, 2006).</p><p>At the end of each <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark>, Chevreul would wash out the glassware using a lot of soap. While conducting his <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark>, Chevreul observed that if he accidentally left soapy water in some glassware and it evaporated overnight, <mark class="term" data-term="salt" data-term-def="Generally, any ionic compound except those that contain hydroxide or hydrogen ions. Specifically, any compound other than water formed by&hellip;" data-term-url="/en/glossary/view/salt/1575">salt</mark> <mark class="term" data-term="crystal" data-term-def="A solid of defined shape that is bound by plane surfaces (facets) that intersect at characteristic angles. The shape of a&hellip;" data-term-url="/en/glossary/view/crystal/1564">crystals</mark> would be left behind. He was confused by this because he had added only water (or another solvent) and soap to the glassware. It raised the question: Where was the salt coming from? Through deductive reasoning, Chevreul realized it must be the result of the soap. When he learned how soap was made by mixing animal or vegetable fat with alkali water, though, he was still confused because there was no salt in <em>that</em> <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> either.</p><p>Intrigued and persistent, Chevreul went on to study the <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> of soap-making in his own laboratory. As he made various kinds of soap, he observed that as oils react with the alkali water, they turn from a translucent <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> into a thick, milky pudding, which gradually hardens. At the time, he knew that oils and fats contain large amounts of carbon and hydrogen and only small amounts of oxygen. He hypothesized that the <mark class="term" data-term="reaction" data-term-def="A chemical change when substances come into contact with each other." data-term-url="/en/glossary/view/reaction/8263">reaction</mark> with the alkali <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark>, which had a high <mark class="term" data-term="pH" data-term-def="A symbol representing a measure of the effective concentration of hydrogen ions in a solution, pH = -log [H<sup>+</sup>]. pH&hellip;" data-term-url="/en/glossary/view/pH/1577">pH</mark> and thus a higher <mark class="term" data-term="concentration" data-term-def="The amount of one substance in relation to other components within a given area." data-term-url="/en/glossary/view/concentration/8733">concentration</mark> of <mark class="term" data-term="hydroxide ion" data-term-def="A negatively charged chemical compound that contains one hydrogen atom and one oxygen atom, written as OH<sup>-</sup>." data-term-url="/en/glossary/view/hydroxide+ion/8513">hydroxide ions</mark> (OH<sup>-</sup>), was somehow adding oxygen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> to the structure of the fats to change them from pure <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbons</mark> to <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> with some salt-like properties. </p><p>This was an excellent <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> because it would explain two different phenomena at the same time. First, it explained the <mark class="term" data-term="salt" data-term-def="Generally, any ionic compound except those that contain hydroxide or hydrogen ions. Specifically, any compound other than water formed by&hellip;" data-term-url="/en/glossary/view/salt/1575">salt</mark> <mark class="term" data-term="crystal" data-term-def="A solid of defined shape that is bound by plane surfaces (facets) that intersect at characteristic angles. The shape of a&hellip;" data-term-url="/en/glossary/view/crystal/1564">crystals</mark> left when soapy water dries. Second, it explained why soap is <mark class="term" data-term="soluble" data-term-def="Capable of being dissolved." data-term-url="/en/glossary/view/soluble/8532">soluble</mark> in both water and oil. The <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbons</mark> from the fat would still be oil-soluble, but their new salt-like properties, coming from the added oxygen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark>, would allow them to be soluble in water, a <mark class="term" data-term="property" data-term-def="A characteristic or attribute." data-term-url="/en/glossary/view/property/8555">property</mark> that all salts have.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7264"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">When soapy water evaporates, it leaves salt crystals behind because</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7264-0-option-a" name="quiz-option-7264" type="radio" value="soap is made from salt mixed with fat." > <span class="option__label"> <span class="screen-reader-only">a.</span> soap is made from salt mixed with fat. </span> </label> <span class="quiz__response" id="response-7264-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7264-1-option-b" name="quiz-option-7264" type="radio" value="hydroxide ions change the structure of fats." > <span class="option__label"> <span class="screen-reader-only">b.</span> hydroxide ions change the structure of fats. </span> </label> <span class="quiz__response" id="response-7264-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>The structure of fats</h2><p>Although it took him most of his career to do it, Chevreul demonstrated that his <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> was correct. He did this by performing painstaking chemical analyses of various fats, oils, and the soaps that are produced when alkali is added to them. Chevreul discovered that, during <mark class="term" data-term="saponification" data-term-def="The process of converting a fat or an oil into soap through combination with an alkali." data-term-url="/en/glossary/view/saponification/7315">saponification</mark>, some of the hydroxide (OH<sup>-</sup>) <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark> from the alkali <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> are indeed added to the <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbons</mark> from the fats. When this happens, some chemical <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> in the fat <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> are broken, releasing long-tailed fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> (Figure 2). Many of the names of common fatty acids that we use today were given to these molecules by Chevreul (Cistola <em>et al.</em>, 1986).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7482.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7482-141201111254.jpg" alt="Figure 2: The basic chemical reaction of saponification." /> </button> <figcaption> <p><strong>Figure 2</strong>: The basic chemical reaction of saponification.</p> </figcaption> </figure> </div> <p>The reason that <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbon</mark> tails from fats are not <mark class="term" data-term="soluble" data-term-def="Capable of being dissolved." data-term-url="/en/glossary/view/soluble/8532">soluble</mark> in water is because almost all of the <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> are symmetrical and thus nonpolar. However, when the <mark class="term" data-term="hydroxide ion" data-term-def="A negatively charged chemical compound that contains one hydrogen atom and one oxygen atom, written as OH<sup>-</sup>." data-term-url="/en/glossary/view/hydroxide+ion/8513">hydroxide ions</mark> break the ester group in fat <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> during <mark class="term" data-term="saponification" data-term-def="The process of converting a fat or an oil into soap through combination with an alkali." data-term-url="/en/glossary/view/saponification/7315">saponification</mark>, a charged and <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark> group is created – a carboxylic <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> group – which is <em>very</em> soluble in water.</p><p>These fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> have a very special structure. They have long chains of nonpolar <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark>, which makes them easily dissolvable in oil and grease; but they also have a <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark> charged group at one end, which makes them easily dissolvable in water. Thus, these <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> have a dual nature – they are both water-soluble (hydrophilic, "loves water") and oil-soluble (lipophilic, "loves fat"). The word for this is <em>amphiphilic</em>, which means "loves both." This is why fatty acids perform so well as soaps and detergents – they are capable of dissolving, and thus cleaning, both watery and greasy substances.</p><p>What Chevreul and others showed was that an alkali <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> breaks up the fat <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> and two parts are released: glycerol and fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark>. We now know the complete structure of the fat molecule (Figure 3).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7483-141201121200.gif" alt="Figure 3: A fat molecule showing its component parts: the glycerol, carboxyl groups, and fatty acids. From Harrigan, G.G., Maguire, G., and Boros, L. 2008. Metabolomics in alcohol research and drug development. Alcohol research Health, 31(1): 27-35." /> </button> <figcaption> <p><strong>Figure 3</strong>: A fat molecule showing its component parts: the glycerol, carboxyl groups, and fatty acids. From Harrigan, G.G., Maguire, G., and Boros, L. 2008. Metabolomics in alcohol research and drug development. <em>Alcohol research Health, 31</em>(1): 27-35.</p> <span class="credit">image ©Harrigan, G., Maguire, G., and Boros, L.</span> </figcaption> </figure> </div> <p>During the <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> of <mark class="term" data-term="saponification" data-term-def="The process of converting a fat or an oil into soap through combination with an alkali." data-term-url="/en/glossary/view/saponification/7315">saponification</mark>, the <mark class="term" data-term="hydroxide ion" data-term-def="A negatively charged chemical compound that contains one hydrogen atom and one oxygen atom, written as OH<sup>-</sup>." data-term-url="/en/glossary/view/hydroxide+ion/8513">hydroxide ions</mark> in the alkali <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> "attack" the ester group and thus release the fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> chains from the glycerol backbone. Chevreul was able to figure this out by analyzing the chemical composition of the fats before the <mark class="term" data-term="reaction" data-term-def="A chemical change when substances come into contact with each other." data-term-url="/en/glossary/view/reaction/8263">reaction</mark>, and then repeating the <mark class="term" data-term="analysis" data-term-def="The careful study of data to look for patterns." data-term-url="/en/glossary/view/analysis/8553">analysis</mark> with the fatty acids that resulted. He did this again and again with different kinds of fats, which made slightly different kinds of soaps. The result was the common theme that fats are made of glycerol and fatty acids.</p></section> <section id="toc_5"> <h2>Fats and oils store energy</h2><p>Animals and plants use fats and oils to store <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark>. As a general rule, fats come from animals and oils come from plants. Because of slight differences in structure, fats are <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> at room temperature and oils are <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> at room temperature. However, both fats and oils are called <em>triglycerides</em> because they have three fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> chains attached to a glycerol <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark>, as shown in Figure 3.</p><p>The carbon-hydrogen <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> (abbreviated C-H) found in the long tails of fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> are high-energy bonds. Thus, triglycerides make excellent storage forms of <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> because they pack many high-energy C-H bonds into a compact structure of three tightly packed fatty acid tails. For this reason, dietary fats and oils are considered "calorie <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark>." When animals, including humans, consume fats and oils, a relatively small <mark class="term" data-term="volume" data-term-def="The amount of space taken up by matter, commonly expressed in cubic centimeters (cm<sup>3</sup>) or milliliters (ml)." data-term-url="/en/glossary/view/volume/8515">volume</mark> can deliver a large number of calories. Animals, particularly carnivores, are drawn to high-fat foods for their high caloric content.</p><p>Triglycerides are formed inside plant and animal <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> by attaching fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> to glycerol <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark>, creating an <em>ester linkage</em>. This <mark class="term" data-term="reaction" data-term-def="A chemical change when substances come into contact with each other." data-term-url="/en/glossary/view/reaction/8263">reaction</mark> is called a <em>dehydration synthesis</em> because a water molecule is formed by "pulling out" two hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> and an oxygen from the <mark class="term" data-term="reactant" data-term-def="The initial material that participates in a chemical reaction. Written on the left side of a chemical equation. Compare&hellip;" data-term-url="/en/glossary/view/reactant/1568">reactants</mark>. Because a new water molecule is formed, this new reaction is also called a <em>condensation reaction</em> (see Figure 4).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7484.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7484-141201121212.jpg" alt="Figure 4: The dehydration synthesis reaction, where a water molecule is formed by "pulling out" two hydrogen atoms and one oxygen atom." /> </button> <figcaption> <p><strong>Figure 4</strong>: The dehydration synthesis reaction, where a water molecule is formed by "pulling out" two hydrogen atoms and one oxygen atom.</p> </figcaption> </figure> </div> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7275"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Fats that we eat are calorie-dense because</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7275-0-option-a" name="quiz-option-7275" type="radio" value="they have many high-energy carbon-hydrogen bonds." > <span class="option__label"> <span class="screen-reader-only">a.</span> they have many high-energy carbon-hydrogen bonds. </span> </label> <span class="quiz__response" id="response-7275-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7275-1-option-b" name="quiz-option-7275" type="radio" value="they come from plants." > <span class="option__label"> <span class="screen-reader-only">b.</span> they come from plants. </span> </label> <span class="quiz__response" id="response-7275-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc2_1"><h3>Structure of fatty acids</h3><p>The reason why fats are <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> at room temperature while oils are <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> has to do with the shape of the fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> these triglycerides contain. Remember that the fatty acids are long chains of carbon <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> that have hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> attached. The C-H <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> are where <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> is stored. At one end of the tail, fatty acids have a carboxyl group (-COOH), which gives the molecule its acidic properties (Figure 5).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7485.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7485-141201121216.jpg" alt="Figure 5: The essential features of a fatty acid showing the long hydrocarbon chain and the carboxylic acid group." /> </button> <figcaption> <p><strong>Figure 5</strong>: The essential features of a fatty acid showing the long hydrocarbon chain and the carboxylic acid group.</p> </figcaption> </figure> </div> <p>If a fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> looks like the <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark> above, with only single <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> between the carbons, we say that this fatty acid is <em>saturated</em>. This term is used because every single carbon is surrounded by as many hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> as is possible; it is <em>saturated</em> with hydrogen.</p><p>However, some fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> have a double <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bond</mark> between two of the carbons in the chain. Wherever this double bond exists, abbreviated C=C, both of the carbons involved in this double bond have one less hydrogen than the other carbons. This is because carbon can only normally make four bonds. When two carbons form a second bond in between them, they each must "let go" of a hydrogen so that the total number of bonds for each carbon is still four. Because these fatty acids have two fewer hydrogen <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atoms</mark> than they otherwise would have, we call them <em>unsaturated</em> fatty acids (Figure 6). They are unsaturated because they <em>do not</em> contain the maximum number of hydrogen atoms that they could have.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7486.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7486-141201121223.jpg" alt="Figure 6: A mono-unsaturated fatty acid." /> </button> <figcaption> <p><strong>Figure 6</strong>: A mono-unsaturated fatty acid.</p> </figcaption> </figure> </div> <p>When a fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> has a double <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bond</mark> in its chain, the chain has a "kink" in its shape because there is no free-rotation around a C=C double bond. The kink is "fixed" in the structure of the fatty acid. In contrast, saturated fatty acids have free rotation around all of the single bonds in the chain since saturated fatty acids are long and straight. A comparison is shown in Figure 7.</p><p>The kinks found in unsaturated fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> make it so that many chains cannot pack together very tightly. Instead, the kinks <mark class="term" data-term="force" data-term-def="An influence (a "push or pull") that changes the motion of a moving object (e.g., slows it down, speeds it up,&hellip;" data-term-url="/en/glossary/view/force/883">force</mark> the fatty acids to push further apart. For this reason, triglycerides with unsaturated fatty acids are <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> at room temperature. Instead of packing together tightly, the <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> can slide past each other easily. The opposite is true for triglycerides with saturated fatty acids. Because their fatty acid tails are straight with no kinks, they can pack together very tightly. Thus, these molecules are more <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark> and <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> at room temperature.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7487.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7487-141201121243.jpg" alt="Figure 7: A comparison of a saturated fatty acid (stearic acid, found in butter) and an unsaturated fatty acid (linoleic acid, found in vegetable oil)." /> </button> <figcaption> <p><strong>Figure 7</strong>: A comparison of a saturated fatty acid (stearic acid, found in butter) and an unsaturated fatty acid (linoleic acid, found in vegetable oil).</p> </figcaption> </figure> </div> <p>Animal fats are often saturated, which explains why lard, bacon fat, and butter are all <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> at room temperature. Plant triglycerides, on the other hand, are typically unsaturated. This is why vegetable oils (such as canola, olive, peanut, etc.) are <mark class="term" data-term="liquid" data-term-def="The state of matter characterized by its condensed nature and ability to flow. Unlike gases, molecules within a liquid often experience&hellip;" data-term-url="/en/glossary/view/liquid/8727">liquid</mark> at room temperature. Most often, unsaturated fats have only one C=C double <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bond</mark> and are thus called <em><u>mono</u>unsaturated</em>. However, some plants make triglycerides with multiple C=C bonds. These kinds of triglycerides are called <em><u>poly</u>unsaturated</em>. (See Figure 8.)</p> <div class="container margin-y-4 text-align-center"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:inline-block;width:300px;height:250px" data-ad-client="ca-pub-9561344156007092" data-ad-slot="3321739899"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7488.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7488-141201121252.jpg" alt="Figure 8: A comparison of the bonds in a monounsaturated fatty acid (oleic acid) and a polyunsaturated fatty acid (linoleic acid)." /> </button> <figcaption> <p><strong>Figure 8</strong>: A comparison of the bonds in a monounsaturated fatty acid (oleic acid) and a polyunsaturated fatty acid (linoleic acid).</p> </figcaption> </figure> </div> <p>Monounsaturated fats appear to be the healthiest triglycerides for humans to consume in their diets because the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> that remove fats from our blood after they are absorbed from our diet do their work most quickly with monounsaturated fats. Because we are slower to remove them from our blood, saturated fats stay in our bloodstream longer and thus have a greater chance to contributing to the formation of plaques and clots. For this reason, doctors and dieticians recommend diets high in monounsaturated fats and low in saturated fats. Polyunsaturated fats are somewhere in between saturated and monounsaturated fats in terms of their healthiness in our diet (Mattson & Grundy, 1985).</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7284"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Saturated fatty acids have ___________ hydrogen atoms than unsaturated fatty acids.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7284-0-option-a" name="quiz-option-7284" type="radio" value="more" > <span class="option__label"> <span class="screen-reader-only">a.</span> more </span> </label> <span class="quiz__response" id="response-7284-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7284-1-option-b" name="quiz-option-7284" type="radio" value="fewer" > <span class="option__label"> <span class="screen-reader-only">b.</span> fewer </span> </label> <span class="quiz__response" id="response-7284-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc2_2"><h3>Trans fats</h3><p>Another type of fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> that has gotten a lot of attention recently is the trans fatty acid. Trans fatty acids have a <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbon</mark> tail with a double <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bond</mark> that is in the <em>trans</em> <mark class="term" data-term="configuration" data-term-def="The way parts are arranged, such as how electrons are distributed in orbitals, or electron shells, around the nucleus of an atom." data-term-url="/en/glossary/view/configuration/8262">configuration</mark>, instead of the more common <em>cis</em> configuration (see Figure 9).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7489.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7489-141201121257.jpg" alt="Figure 9: A comparison of the cis double-bond configuration and the trans double-bond configuration." /> </button> <figcaption> <p><strong>Figure 9</strong>: A comparison of the cis double-bond configuration and the trans double-bond configuration.</p> </figcaption> </figure> </div> <p>As discussed above, C=C double <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> are present in the fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> tails of unsaturated fats. When these unsaturated fatty acids are made naturally by living <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>, most often plant cells, the C=C double bonds are always in the cis <mark class="term" data-term="configuration" data-term-def="The way parts are arranged, such as how electrons are distributed in orbitals, or electron shells, around the nucleus of an atom." data-term-url="/en/glossary/view/configuration/8262">configuration</mark>, almost never in the <em>trans</em> configuration. However, during industrial production of certain fat-containing <mark class="term" data-term="product" data-term-def="The material that is formed as a result of a chemical reaction. Written on the right side of a chemical equation.&hellip;" data-term-url="/en/glossary/view/product/1569">products</mark>, the <em>trans</em> configuration can be inadvertently formed. This occurs when unsaturated fats, usually vegetable oils, are subjected to the <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> of <mark class="term" data-term="hydrogenation" data-term-def="A chemical process in which hydrogen is added to the double bonds of unsaturated fats, usually vegetable oils, to create a&hellip;" data-term-url="/en/glossary/view/hydrogenation/7317">hydrogenation</mark> in order to turn them into saturated fats (shown in Figure 10).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7490.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7490-141201011203.jpg" alt="Figure 10: Unsaturated fats, usually vegetable oils, are subjected to the process of hydrogenation in order to turn them into saturated fats." /> </button> <figcaption> <p><strong>Figure 10</strong>: Unsaturated fats, usually vegetable oils, are subjected to the process of hydrogenation in order to turn them into saturated fats.</p> </figcaption> </figure> </div> <p>The purpose of industrial <mark class="term" data-term="hydrogenation" data-term-def="A chemical process in which hydrogen is added to the double bonds of unsaturated fats, usually vegetable oils, to create a&hellip;" data-term-url="/en/glossary/view/hydrogenation/7317">hydrogenation</mark> is to create <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> fats, which are more desirable for deep-frying, out of vegetable oils. This is done because vegetable oils are much less expensive than naturally saturated fats such as lard. Crisco™ and margarine are two such chemically-produced saturated fats that are made of hydrogenated vegetable oils. Crisco™, or shortening, is cheaper than lard but can be used similarly and gives similar taste. Margarine, or oleo, was developed as a cheaper substitute for butter, particularly during the era of the World Wars and global depressions that marked the first half of the 20<sup>th</sup> century, when rationing and scarcity of staples was common. Today, many packaged desserts and candies also have these kinds of industrially produced saturated fats, which often cost less than natural saturated fats but provide better texture and firmness than unsaturated fats. During hydrogenation, occasionally the <mark class="term" data-term="chemical reaction" data-term-def="A process in which atoms and molecules recombine by forming or breaking chemical bonds. Chemical reactions form new products that&hellip;" data-term-url="/en/glossary/view/chemical+reaction/1547">chemical reaction</mark> does not go to completion and the <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> of turning a cis unsaturated fat into a saturated fat creates a trans fat instead.</p><p>In recent years, trans fats have received a lot of attention from dieticians and the general public because of their association with elevated health risks. Individuals with diets higher in trans fats are more likely to develop coronary heart disease, suffer heart attacks and stroke, and die earlier than those with diets low in trans fats (Mensink & Katan, 1990). It was always known that <mark class="term" data-term="hydrogenation" data-term-def="A chemical process in which hydrogen is added to the double bonds of unsaturated fats, usually vegetable oils, to create a&hellip;" data-term-url="/en/glossary/view/hydrogenation/7317">hydrogenation</mark> produces some trans fats, but because they are not acutely toxic, their long-term health dangers are only now being realized.</p><p>Scientists have discovered the reason for these elevated risks: Trans fats spend a much longer amount of time in our bloodstream after we consume them, instead of being quickly absorbed into our <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>. Unlike saturated fats and cis unsaturated fats, trans fats don't appear in nature in very large amounts – they are an "unnatural" form of fat which humans are not well designed to consume. Because humans only began to eat trans fats in the 20<sup>th</sup> century (other than the very tiny amounts that are present in some forms of red meat), we do not have receptor <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> in our blood vessels that seek out these trans fats and remove them from the bloodstream. Thus, when we consume trans fats, they persist in our bloodstream for a very long time, compared to natural forms of fat. The longer these molecules spend in our bloodstream, the more they can contribute to the formation of clots, plaques, and hardened arteries. For this reason, the United States Food and Drug Administration has recently made a preliminary determination that trans fats are “not generally recognized as safe,” a determination that will likely lead to a complete ban on their presence in foodstuffs (Brownell & Pomeranz, 2014).</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7291"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Trans fats are </span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7291-0-option-a" name="quiz-option-7291" type="radio" value="they are made from vegetable oil." > <span class="option__label"> <span class="screen-reader-only">a.</span> they are made from vegetable oil. </span> </label> <span class="quiz__response" id="response-7291-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7291-1-option-b" name="quiz-option-7291" type="radio" value="they stay in our bloodstream for a long time." > <span class="option__label"> <span class="screen-reader-only">b.</span> they stay in our bloodstream for a long time. </span> </label> <span class="quiz__response" id="response-7291-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_6"> <h2>Phospholipids and glycolipids form cellular membranes</h2><p>Perhaps the most important and basic function of <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> in living <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> is in the formation of cellular <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark>. All cells, from the most basic bacterium to those that form the most specialized human tissues, are surrounded by a <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membrane</mark> made of lipid <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark>. For more detail, see the <a href="/en/library/Biology/2/Membranes-I/198">Membranes I: Introduction to Biological Membranes</a> module.</p><p>The <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark> that form <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> are a special type called <mark class="term" data-term="phospholipid" data-term-def="A lipid or glyceride that contains a phosphate group. The phosphate group imparts a polar side to the molecule, while&hellip;" data-term-url="/en/glossary/view/phospholipid/2567">phospholipids</mark> (Figure 11). They are so named because they have a characteristic phosphate group (PO<sub>4</sub>). Like triglycerides, the central structure of a phospholipid is the glycerol <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark>. However, phospholipids have two fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acid</mark> tails attached to the glycerol, whereas triglycerides have three. On the remaining carbon of the glycerol, a large, charged, phosphate-containing group is added.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7491.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7491-141201011225.jpg" alt="Figure 11: A phospholipid." /> </button> <figcaption> <p><strong>Figure 11</strong>: A phospholipid.</p> <span class="credit">image ©OpenStax College</span> </figcaption> </figure> </div> <p>This distinctive head group gives <mark class="term" data-term="phospholipid" data-term-def="A lipid or glyceride that contains a phosphate group. The phosphate group imparts a polar side to the molecule, while&hellip;" data-term-url="/en/glossary/view/phospholipid/2567">phospholipids</mark> their unique properties. Like fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark>, the presence of a <mark class="term" data-term="hydrophobic" data-term-def="Literally meaning "water fearing," a substance that has little affinity for water. Generally, non-polar molecules that do not dissolve in&hellip;" data-term-url="/en/glossary/view/hydrophobic/1600">hydrophobic</mark> tail and a <mark class="term" data-term="hydrophilic" data-term-def="Literally meaning "water loving," a substance that readily associates with water. Often polar molecules or some ionic molecules that easily&hellip;" data-term-url="/en/glossary/view/hydrophilic/1601">hydrophilic</mark> head means that phospholipids are <mark class="term" data-term="amphiphilic" data-term-def="(from the Greek <em>amphi</em>, "both," and <em>philic</em>, "loves," so together it means "loves both") Molecules that are both water-soluble (hydrophilic) and&hellip;" data-term-url="/en/glossary/view/amphiphilic/7316">amphiphilic</mark>. This distinctive structure leads to a very peculiar behavior by phospholipids – the spontaneous formation of bilayers. When phospholipid <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> are placed into an aqueous <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> (water-based), they will arrange themselves into sphere-shaped structures in which the <mark class="term" data-term="surface" data-term-def="The outside or external part; the topside face of something." data-term-url="/en/glossary/view/surface/8275">surface</mark> of the sphere is a double layer of phospholipids. While the hydrophilic head groups are attracted to the water in the surrounding solution, the hydrophobic tails are repelled by it and attracted to each other. This means that the most “comfortable” arrangement for the phospholipids to take is to tuck their tails together in a water-free interior space, with the <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark> head groups facing out, interacting with water (Figure 12) – this is called a micelle<. You can learn more about the ways in which phospholipids function in the <a href="/en/library/Biology/2/Membranes-I/198">Membranes I: Introduction to Biological Membranes</a> module.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_9571.png" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-9571-160415010441.png" alt="Figure 12: Three of the different structures phospholipids can form in an aqueous solution: micelle, liposome, and bilayer sheet. In this depiction, the hydrophilic heads are round and white and the hydrophobic tails are yellow wavy lines." /> </button> <figcaption> <p><strong>Figure 12</strong>: Three of the different structures phospholipids can form in an aqueous solution: micelle, liposome, and bilayer sheet. In this depiction, the hydrophilic heads are round and white and the hydrophobic tails are yellow wavy lines.</p> </figcaption> </figure> </div> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7296"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Cell membranes have a __________ layer of lipid molecules.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7296-0-option-a" name="quiz-option-7296" type="radio" value="double" > <span class="option__label"> <span class="screen-reader-only">a.</span> double </span> </label> <span class="quiz__response" id="response-7296-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7296-1-option-b" name="quiz-option-7296" type="radio" value="triple" > <span class="option__label"> <span class="screen-reader-only">b.</span> triple </span> </label> <span class="quiz__response" id="response-7296-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_7"> <h2>Steroids provide structure and <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> signaling</h2><p>Another class of lipid <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> that are important in <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> are the steroids, also called sterols. Unlike triglycerides and <mark class="term" data-term="phospholipid" data-term-def="A lipid or glyceride that contains a phosphate group. The phosphate group imparts a polar side to the molecule, while&hellip;" data-term-url="/en/glossary/view/phospholipid/2567">phospholipids</mark> with their long <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbon</mark> tails, steroids consist of four fused carbon rings, as shown in Figure 13. As you would expect because of all of the nonpolar C-H <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark>, steroids are not <mark class="term" data-term="soluble" data-term-def="Capable of being dissolved." data-term-url="/en/glossary/view/soluble/8532">soluble</mark> in water.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7493.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7493-141201041201.jpg" alt="Figure 13: The generic structure of a steroid molecule and the structure of cholesterol." /> </button> <figcaption> <p><strong>Figure 13</strong>: The generic structure of a steroid molecule and the structure of cholesterol.</p> </figcaption> </figure> </div> </section> <section id="toc2_3"><h3>Cholesterol</h3><p>The most fundamental steroid <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark> is cholesterol because all of the other steroids that are made from it. Cholesterol has its own functions as well. For example, in animal <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>, cholesterol is embedded in cell <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> to give them fluidity and to prevent them from solidifying in cold temperatures. Plants contain molecules similar to cholesterol called <em>phytosterols</em> that perform similar functions.</p><p>Cholesterol was named by Michel Chevreul in 1815, who found that human gallstones have a large amount of this lipid. A century later, Alfred Windaus and Henrich Wieland confirmed that the liver made cholesterol, although they deduced its structure incorrectly. They shared the <mark class="term" data-term="Nobel Prize" data-term-def="Awards made annually, beginning in 1901, from funds originally established by Alfred B. Nobel for outstanding achievement in physics, chemistry, medicine&hellip;" data-term-url="/en/glossary/view/Nobel+Prize/3843">Nobel Prize</mark> in 1928 for their discovery that cholesterol and other bile <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> are made by the liver and used to dissolve dietary fats so that they can be absorbed by the intestines. The correct structure of cholesterol wasn't confirmed until 1945, when Dorothy Crowfoot Hodgkin used the new technique of <mark class="term" data-term="X-ray" data-term-def="A form of electromagnetic radiation with higher frequency and energy than any other electromagnetic radiation besides gamma rays. X-rays have various&hellip;" data-term-url="/en/glossary/view/X~ray/7573">X-ray</mark> <mark class="term" data-term="diffraction" data-term-def="The bending or spreading of waves when they meet an obstruction." data-term-url="/en/glossary/view/diffraction/3606">diffraction</mark> (see Figure 14) to realize the precise arrangement of the four-ring structure (Bloch, 1982).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7494.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7494-141201041207.jpg" alt="Figure 14: An x-ray diffraction pattern." /> </button> <figcaption> <p><strong>Figure 14</strong>: An x-ray diffraction pattern.</p> <span class="credit">image ©Jeff Dahl</span> </figcaption> </figure> </div> </section> <section id="toc2_4"><h3>Other steroids</h3><p>There are many other steroids, but all of them, by definition, are cholesterol derivatives (Figure 15). That is, they are made using cholesterol as the starting material. Many of these steroids are <mark class="term" data-term="hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;" data-term-url="/en/glossary/view/hormone/10183">hormones</mark>, such as the sex steroids estrogen, progesterone, testosterone, and their cousins. Other steroid <mark class="term" data-term="hormone" data-term-url="/en/glossary/view/hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;">hormones</mark> include <mark class="term" data-term="cortisol" data-term-def="One of the hormones synthesized in the adrenal cortex. It stimulates synthesis of glucose from protein and fat and suppresses inflammation&hellip;" data-term-url="/en/glossary/view/cortisol/10176">cortisol</mark> and aldosterone.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7495.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7495-141202091242.jpg" alt="Figure 15: A chart of the steroid hormones and their biosynthetic relationships." /> </button> <figcaption> <p><strong>Figure 15</strong>: A chart of the steroid hormones and their biosynthetic relationships.</p> <span class="credit">image ©David Richfield and Mikael Häggström</span> </figcaption> </figure> </div> <p>Although these <mark class="term" data-term="hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;" data-term-url="/en/glossary/view/hormone/10183">hormones</mark> all perform widely differing functions in the body, they have a strikingly similar structure. This common structure means that they have a similar mechanism of action. Steroid <mark class="term" data-term="hormone" data-term-url="/en/glossary/view/hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;">hormones</mark> are released by glands and then travel throughout the body where they exert their actions by binding to their receptors inside of <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> and then activating or de-activating <mark class="term" data-term="gene" data-term-def="Material (usually DNA) that is inherited from a parent and which encodes for a cellular component important for some cellular function." data-term-url="/en/glossary/view/gene/3294">genes</mark>. The power of steroid hormones is in their lipid nature, which allows them to cross biological <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> easily. Thus, a hormone produced in one tissue will quickly and easily <mark class="term" data-term="diffusion" data-term-url="/en/glossary/view/diffusion" data-term-def="The movement of atoms or molecules from one part of a medium to another caused by their random thermal motion.&hellip;">diffuse</mark> throughout the entire body, passing through cells as easily as oxygen and carbon dioxide do (see Figure 16.)</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7496.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7496-141202091247.jpg" alt="Figure 16: A steroid hormone receptor's mechanism of action." /> </button> <figcaption> <p><strong>Figure 16</strong>: A steroid hormone receptor's mechanism of action.</p> <span class="credit">image ©Designua</span> </figcaption> </figure> </div> </section> <section id="toc_8"> <h2>Other lipids</h2><p>Several other sorts of <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compounds</mark> are grouped in with the lipid family because they are <mark class="term" data-term="insoluble" data-term-def="Unable to be dissolved." data-term-url="/en/glossary/view/insoluble/8732">insoluble</mark> in water.</p></section> <section id="toc2_5"><h3>Carotenoids</h3><p>The <mark class="term" data-term="pigment" data-term-def="A light-absorbing molecule that gathers energy from the sun; a molecule that gives color and is involved in vital functions within&hellip;" data-term-url="/en/glossary/view/pigment/8522">pigments</mark> that give some plants their orange and yellow color (e.g., carrots and summer squash) are carotenoids. They contain branching five-carbon chains called isoprene units (see Figure 17). Animals are able to break down these <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> into vitamin A, which may then be used to produce retinal, a pigment necessary for eyesight.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7498.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7498-141202121246.jpg" alt="Figure 17: Isoprene units contain branching five-carbon chains. Animals are able to break down these molecules into vitamin A." /> </button> <figcaption> <p><strong>Figure 17</strong>: Isoprene units contain branching five-carbon chains. Animals are able to break down these molecules into vitamin A.</p> </figcaption> </figure> </div> </section> <section id="toc2_6"><h3>Waxes</h3><p>Waxes appear in many different living things, providing the natural coating on some leaves and fruits, the sheen on the feathers of some birds, the shine on human hair, and the protective secretions in our ear canals. Like triglycerides, waxes are esters of fatty <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark>, consisting of an <mark class="term" data-term="alcohol" data-term-def="An organic compound containing a hydroxyl group. Common examples include methanol (CH<sub>3</sub>OH) and ethanol (CH<sub>3</sub>CH<sub>2</sub>OH)." data-term-url="/en/glossary/view/alcohol/1592">alcohol</mark> <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark> bonded to fatty acids through ester linkage. Wax is strongly <mark class="term" data-term="hydrophobic" data-term-def="Literally meaning "water fearing," a substance that has little affinity for water. Generally, non-polar molecules that do not dissolve in&hellip;" data-term-url="/en/glossary/view/hydrophobic/1600">hydrophobic</mark>, and thus serves as an effective water repellant. In addition, the fully saturated <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbon</mark> chains of wax molecules makes them <mark class="term" data-term="solid" data-term-def="A collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and&hellip;" data-term-url="/en/glossary/view/solid/7571">solid</mark> at room temperature, like saturated fats discussed earlier (see Figure 18).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7499.jpg" data-lightbox="image"> <img src="/img/library/modules/mid207/Image/VLObject-7499-141202121252.jpg" alt="Figure 18: A wax molecule showing the long-chain alcohol and fatty acid." /> </button> <figcaption> <p><strong>Figure 18</strong>: A wax molecule showing the long-chain alcohol and fatty acid.</p> </figcaption> </figure> </div> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc7311"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Some lipids are manufactured in the human body.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7311-0-option-a" name="quiz-option-7311" type="radio" value="true" > <span class="option__label"> <span class="screen-reader-only">a.</span> true </span> </label> <span class="quiz__response" id="response-7311-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7311-1-option-b" name="quiz-option-7311" type="radio" value="false" > <span class="option__label"> <span class="screen-reader-only">b.</span> false </span> </label> <span class="quiz__response" id="response-7311-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_9"> <h2>Lipid research and medical science</h2><p>Lipids play a role in eyesight, nerve tissue, vitamin absorption, the endocrine <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark>, and many other body functions. Scientists have known that some fat is carried in the bloodstream ever since the late 1600s, when researchers examined the blood of animals that had just eaten a fatty meal and discovered that it briefly turned milky and yellowish. Now it’s clear that an excess of cholesterol in the blood can lead to deposits called plaque in <mark class="term" data-term="artery" data-term-def="A blood vessel that conveys oxygenated blood away from the heart to other parts of the body." data-term-url="/en/glossary/view/artery/5268">artery</mark> walls, which increases a person’s risk of heart attack. <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">Research</mark> into these fatty plaques has revealed that trans fats strongly exacerbate their formation, given how much longer they persist in the bloodstream. In addition, chemicals from cigarette smoke have been shown to increase the inflammatory response that gradually turns these fatty deposits into plaques and then to obstructive clots. Fortunately, arterial plaques are dynamic, and their formation can be reversed by stopping smoking and transitioning to a diet lower in cholesterol and fats from the saturated and trans fats family.</p><p>Ongoing <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> in lipid chemistry advances medical knowledge as we seek to understand and treat high cholesterol, heart disease, <mark class="term" data-term="hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;" data-term-url="/en/glossary/view/hormone/10183">hormone</mark> disorders, thyroid disease, fatty liver disease, multiple sclerosis, autism spectrum disorder, macular degeneration, Guillain-Barré syndrome, and other conditions.</p></section> <footer class="module__main__footer"> <hr class="border-color-dark"> <p class="citation"> <em> Nathan H Lents, Ph.D., Lizzie Stark, M.S./M.F.A, Bonnie Denmark, M.A./M.S. “Lipids” Visionlearning Vol. BIO-4 (1), 2014. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li><p></li> <li>Bloch, K. (1982). The structure of cholesterol and of the bile acids. <em>Trends in Biochemical Sciences, 7</em>(9), 334-336.</li> <li>Brownell, K. D., & Pomeranz, J. L. (2014). The trans-fat ban: Food regulation and long-term health. <em>New England Journal of Medicine, 370</em>(19), 1773-1775.</li> <li>Cistola, D. P., Atkinson, D., Hamilton, J. A., & Small, D. M. (1986). Phase behavior and bilayer properties of fatty acids: hydrated 1:1 acid-soaps. <em>Biochemistry, 25</em>(10), 2804-2812.</li> <li>Levey, M. (1954). The early history of detergent substances: A chapter in Babylonian chemistry. <em>Journal of Chemical Education, 31</em>(10), 521-524.</li> <li>Mattson, F. H., & Grundy, S. M. (1985). Comparison of effects of dietary saturated, monounsaturated, and polyunsaturated fatty acids on plasma lipids and lipoproteins in man. <em>Journal of Lipid Research, 26</em>(2), 194-202.</li> <li>McNamara, J. R., Warnick, G. R., & Cooper, G. R. (2006). A brief history of lipid and lipoprotein measurements and their contribution to clinical chemistry. <em>Clinica Chimica Acta, 369</em>(2), 158-167.</li> <li>Mensink, R. P., & Katan, M. B. (1990). Effect of dietary trans fatty acids on high-density and low-density lipoprotein cholesterol levels in healthy subjects. <em>New England Journal of Medicine, 323</em>(7), 439-445.</li> </ul> </div>  <div class="title-list" name="further"> <p class="h6 title-list__title"> Further Reading </p> <ul class="grid grid--column-2--md grid--column-3--md gap-1"> <li> <a class="no-hover-focus height-100" href="/en/library/Biology/2/Membranes-I/198"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_198-23061209062656.jpeg" alt="Membranes I"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Membranes I: <em>Structure and function of biological membranes</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Biology/2/Membranes-II/204"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_204-23061209062709.jpg" alt="Membranes II"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Membranes II: <em>Passive and active transporters</em> </h2> </div> </article> </a> </li> </ul> </div> </footer> </div>    </article> </div> </div> </main>   <footer class="position-relative box-shadow-1 font-size-md" id="global-footer"> <h2 class="screen-reader-only">Page Footer</h2> <div class="back-to-top"> <div class="container wide"> <button class="button button--has-icon font-size-sm"> <span class="icon icon-arrow-up"></span> <span class="button__text">Back to top</span> </button> </div> </div> <div class="container wide padding-y-2"> <div class="grid grid--column-2--md grid--column-4--lg gap-4 grid--divider--fill-x"> <nav> <ul class="nav font-weight-bold"> <li> <a href="/en/library" title="Readings & quizzes"> Library </a> </li> <li> <a href="/en/glossary" title="Science terms"> Glossary </a> </li> <li> <a href="/en/classroom" title="Courses & bookmarks"> Classroom </a> </li> </ul> </nav> <nav> <ul class="nav"> <li><a href="/en/about">About</a></li> <li><a href="/en/help">Contact</a></li> <li><a href="/en/about/jobs">Jobs</a></li> <li><a href="/en/help/faq">FAQ</a></li> </ul> </nav> <div> <ul class="nav nav--horizontal margin-bottom-2"> <li> <a class="display-flex" href="https://www.nsf.gov" target="_blank" rel="noopener"> <img src="/images/sponsor-nsf.png" width="60" height="60" alt="US Education Department Logo" /> </a> </li> <li> <a class="display-flex" href="https://www.ed.gov/" target="_blank" rel="noopener"> <img src="/images/sponsor-doe.png" width="60" height="60" alt="US Education Department Logo" /> </a> </li> </ul> <p>Visionlearning is supported by the The National Science Foundation and the U.S. Department of Education. The views expressed here do not represent the views of our funders.</p> <p><a href="/en/about/sponsorship">Sponsorships</a></p> </div> <nav class="font-size-sm"> <p> <strong>Follow Visionlearning</strong> </p> <ul class="nav nav--has-icons"> <li> <a href="https://www.facebook.com/pages/Visionlearning/129614736696" target="_blank" rel="noopener"> <span class="icon icon-facebook"></span> <span class="nav__text">Facebook</span> </a> </li> <li> <a href="https://twitter.com/visionlearning" target="_blank" rel="noopener"> <span class="icon icon-twitter"></span> <span class="nav__text">Twitter</span> </a> </li> <li> <a href="https://www.youtube.com/c/visionlearning" target="_blank" rel="noopener"> <span class="icon icon-youtube"></span> <span class="nav__text">YouTube</span> </a> </li> </ul> </nav> </div> </div> <hr /> <div class="container wide"> <div class="copyright padding-y-2"> <ul class="nav nav--horizontal font-size-sm"> <li>© 2000-2025 Visionlearning, Inc.</li> <li><a href="/en/terms#privacy">Privacy Policy</a></li> <li><a href="/terms">Terms of Service</a></li> </ul> </div> </div> </footer>  <script src="/js/jquery-3.7.1.min.js"></script> <script src="/js/script_rsd.js"></script> <script type="text/javascript"> $(document).ready( function () { var x = $('#ngssCommentdata').html(); if(!!x){ var jsonObjs = JSON.parse(x); for (var i=0; i < jsonObjs.length; i++){ var item = jsonObjs[i]; var id = item.mod_ngss_comment_id; var ngss = "ngss-"+id; var tag = document.getElementById(ngss); if(!!tag){ if(item.type == "p"){ item.type = 'Practice'; item.typeFull = 'Science and Engineering Practices'; } if(item.type == "dci"){ item.type = 'Core Idea'; item.typeFull = 'Disciplinary Core Ideas'; } if(item.type == "cc"){ item.typeFull = 'Crosscutting Concepts'; item.type = 'Crosscutting'; } tag.classList.add( 'ngss'); tag.setAttribute('data-ngss-cat-abbr', item.type); tag.setAttribute('data-ngss-cat-full', item.typeFull); tag.setAttribute('data-ngss-comment', item.comment.trim()); tag.setAttribute('data-ngss-desc', item.comment.trim()); if(item.tag){ tag.setAttribute('data-ngss-standard', item.tag.trim()); //tag.setAttribute('data-ngss-tag', item.tag); //tag.setAttribute('data-ngss-desc', item.description); } } console.log( "Item ID " + item.mod_ngss_comment_id + "\nDimension " + item.dimension + "\nType : " + item.type); } } }); function loadObjMaker(target, type_id, url){ console.log("Loading "+ url +" target " + target); if($(target).load(url)){ // alert("It should be loaded. " + url + " target " + target); } return false; } function closeEmbbed(div){ $(div).empty(); } </script>   <script async src="https://www.googletagmanager.com/gtag/js?id=G-GEPQ8CJNEN"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-GEPQ8CJNEN'); </script> <script src="/js/visionlearning.js"></script> </body> </html>

CINXE.COM

Lipids | Biology | Visionlearning