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class="comp article-header-block mntl-block "><ul id="breadcrumbs_1-0" class="comp breadcrumbs mntl-universal-breadcrumbs mntl-block type--squirrel breadcrumbs" data-tracking-container="true"><li id="mntl-breadcrumbs__item_1-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/sciences-math-4132465" rel="nocaes" id="mntl-text-link_5-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Science, Tech, Math</span></a> <span id="breadcrumbs__separator_1-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li> <li id="mntl-breadcrumbs__item_2-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/science-4132464" rel="nocaes" id="mntl-text-link_6-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Science</span></a> <span id="breadcrumbs__separator_2-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li> <li id="mntl-breadcrumbs__item_3-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/biology-4133580" rel="nocaes" id="mntl-text-link_7-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Biology</span></a> <span id="breadcrumbs__separator_3-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li> <li id="mntl-breadcrumbs__item_4-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/biology-cells-4133579" rel="nocaes" id="mntl-text-link_8-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Cell Biology</span></a> <span id="breadcrumbs__separator_4-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li></ul> <div id="article-heading_1-0" class="comp article-heading mntl-article-header"> <h1 class="article-heading type--lion">Proteins in the Cell</h1> </div></div> </div><div class="loc article-post-header"><div id="post-header-social-block_1-0" class="comp post-header-social-block mntl-block"><div id="social-share-block_1-0" class="comp social-share-block mntl-block"><ul id="social-share_1-0" class="comp social-share mntl-social-share share" data-title="Proteins in the Cell" document="StructuredContentDocumentEx{parent=BaseDocumentEx{templateType=STRUCTUREDCONTENT, documentId=373550, bestTitle='Proteins in the Cell'}}" data-description="Proteins are very important molecules in human cells. They are constructed from amino acids and each protein within the body has a specific function." data-tracking-container="true"> <li class="share-item share-item-facebook"> <span data-href="https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fwww.thoughtco.com%2Fprotein-function-373550%3Futm_source%3Dfacebook.com%26utm_medium%3Dsocial%26utm_campaign%3Dsocial-share-article" data-network="facebook" data-click-tracked="true" class="share-link share-link-facebook" tabindex="0" title="Share on Facebook" aria-label="Share on Facebook" role="link"> <svg class="icon icon-facebook " > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-facebook" href="#icon-facebook"></use> </svg> </span> </li> <li class="share-item share-item-flipboard"> <span data-href="https://share.flipboard.com/bookmarklet/popout?v=2&url=https%3A%2F%2Fwww.thoughtco.com%2Fprotein-function-373550%3Futm_source%3Dflipit%26utm_medium%3Dweb%26utm_campaign%3Dwidgets%26utm_content%3Dwww.thoughtco.com&title=Proteins+in+the+Cell&t=1739846194255" data-network="flipboard" data-click-tracked="true" class="share-link share-link-flipboard" tabindex="0" title="Share on Flipboard" aria-label="Share on Flipboard" role="link"> <svg class="icon icon-flipboard " > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-flipboard" href="#icon-flipboard"></use> </svg> </span> </li> <li class="share-item share-item-email"> <span data-href="https://www.thoughtco.com/protein-function-373550?utm_source=emailshare&utm_medium=social&utm_campaign=shareurlbuttons" data-network="emailshare" data-click-tracked="true" class="share-link share-link-email" tabindex="0" title="Email this article" aria-label="Email this article" role="link"> <svg class="icon icon-envelope " > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-envelope" href="#icon-envelope"></use> </svg> </span> </li> </ul></div> <form id="print-button_1-0" class="comp print-button" method="POST" action="/protein-function-373550?print" target="_blank"> <button class="mntl-print-button__btn" aria-label="Print this article."> Print <svg class="icon icon-print mntl-print-button__icon" > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-print" href="#icon-print"></use> </svg> </button> <input type="hidden" value="true" name="print" /> <input type="hidden" value="239c1f866d8d35c4fe96a78c70c2930c" name="CSRFToken" /> </form></div> <figure id="figure-article_1-0" class="comp figure-article mntl-universal-primary-image lock-primary right-rail__offset figure-landscape primary-image"> <div class="primary-image__media"> <div class="img-placeholder" style="padding-bottom:66.6%;"> <img src="https://www.thoughtco.com/thmb/Xw8aZYFwT4YMmyrXXDCiO4ctzsw=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/protein-hemoglobin-58a222955f9b58819ca8f902.jpg" width="1500" height="1000" srcset="https://www.thoughtco.com/thmb/Xw8aZYFwT4YMmyrXXDCiO4ctzsw=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/protein-hemoglobin-58a222955f9b58819ca8f902.jpg 1500w" sizes="750px" alt="This is a molecular model of the protein hemoglobin. This molecule transports oxygen around the body in red blood cells. It consists of four globin proteins (amino acid chains; green, yellow, blue and pink)." class=" primary-image__image mntl-primary-image--blurry" onload="(function(e){e.classList.add('loaded')})(this)" style="--blurry: url('data:image/gif;charset=utf-8;base64,R0lGODlhCgAHAPUAAAMAAgICAAgDCRMcGyITDjo9XgBWOABrTQBzTTlDdkU9O1A0KVs6b3lEMkFKa1lhY3hcUD5OjEBQm3xQm2ZyrHCEhXeFxHrexIhGOpd5brRzbYphp5ek6Kav5ojNsNiehtagiN2vmNy2oe6YgfO3n+C4tta26NTu7d357f7//////wMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAgMAAiwAAAAACgAHAEUIPwBVCDyAQgQIgQIvUGDQwUGJBghTWDCQAQCBDwgFRpDAoUJGFQM8hBgBQQNCBAIKBMBAQsEChCYmJNjw4ITAgAA7')" /> <noscript> <img src="https://www.thoughtco.com/thmb/Xw8aZYFwT4YMmyrXXDCiO4ctzsw=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/protein-hemoglobin-58a222955f9b58819ca8f902.jpg" width="1500" height="1000" class="loaded primary-img--noscript primary-image__image mntl-primary-image--blurry" srcset="https://www.thoughtco.com/thmb/Xw8aZYFwT4YMmyrXXDCiO4ctzsw=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/protein-hemoglobin-58a222955f9b58819ca8f902.jpg 1500w" sizes="750px" alt="This is a molecular model of the protein hemoglobin. This molecule transports oxygen around the body in red blood cells. It consists of four globin proteins (amino acid chains; green, yellow, blue and pink)." /> </noscript> </div> </div> <figcaption id="primary-image__figcap_1-0" class="comp primary-image__figcap mntl-figure-caption figure-article-caption"> <span class="figure-article-caption-owner">Laguna Design / Science Photo Library / Getty Images</span> </figcaption></figure> </div><div class="loc article-left-rail"> <div id="breadcrumbs-list_2-0" class="comp breadcrumbs-list " data-tracking-container="true"><a href="https://www.thoughtco.com/science-4132464" rel="nocaes" class="breadcrumbs-list-image" ><div class="loc image"><img src="https://www.thoughtco.com/thmb/GlGRAYLjgFbTQlbxhxfdvvPh9L8=/150x0/filters:no_upscale():max_bytes(150000):strip_icc()/left_rail_image_science-58a22da268a0972917bfb5cc.png" width="150" height="0" alt="Science" class=" universal-image__image" /> </div></a> <span class="breadcrumbs-list-title"> <a href="https://www.thoughtco.com/science-4132464" rel="nocaes" >Science</a> 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class="comp mntl-bylines__group mntl-block mntl-bylines__group--author"><div id="mntl-bylines__item_1-0" class="comp mntl-bylines__item mntl-attribution__item mntl-attribution__item--has-date"> <span class="mntl-attribution__item-descriptor">By</span> <div data-tooltip="Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists."" tabindex="0" data-inline-tooltip="true"> <a href="https://www.thoughtco.com/regina-bailey-372397" rel="nocaes" data-trigger-link="true" class="mntl-attribution__item-name" tabindex="-1" >Regina Bailey</a> <div id="mntl-author-tooltip_1-0" class="comp mntl-author-tooltip mntl-tooltip mntl-group "> <div class="mntl-author-tooltip__top mntl-author-tooltip__top--no-image"> <div id="mntl-author-tooltip__name_1-0" class="comp mntl-author-tooltip__name mntl-attribution__item "> <a href="https://www.thoughtco.com/regina-bailey-372397" rel="nocaes" class="mntl-attribution__item-name" tabindex="0" >Regina Bailey</a> </div> <span id="mntl-author-tooltip__job-title_1-0" class="comp mntl-author-tooltip__job-title mntl-text-block">Biology Expert</span> <ul id="mntl-author-tooltip__education_1-0" class="comp mntl-author-tooltip__education mntl-block"><li id="mntl-author-tooltip__education-item_1-0" class="comp mntl-author-tooltip__education-item mntl-text-block">B.A., Biology, Emory University</li> <li id="mntl-author-tooltip__education-item_2-0" class="comp mntl-author-tooltip__education-item mntl-text-block">A.S., Nursing, Chattahoochee Technical College</li></ul> <div class="mntl-author-tooltip__bio"> Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." </div> </div> <div class="mntl-author-tooltip__bottom"> <span class="mntl-author-tooltip__learn-more-text">Learn about our</span> <a href="/about-us-4779650#toc-editorial-guidelines" rel="nocaes" class="mntl-author-tooltip__learn-more-link" >Editorial Process</a> </div> </div></div> </div> <div class="mntl-attribution__item-date">Updated on January 23, 2020</div></div> </div></div> </div><div class="loc article-content"><div id="article-content_1-0" class="comp article-content mntl-block"><div id="mntl-sc-page_1-0" class="comp mntl-sc-page mntl-block structured-content expert-content" data-sc-sticky-offset="85" data-sc-ad-label-height="24" data-sc-ad-track-spacing="100" data-sc-min-track-height="250" data-sc-max-track-height="600" data-sc-breakpoint="50em" data-sc-load-immediate="3" data-sc-content-positions="[1, 1050, 1250, 1550, 1950, 2350, 2750, 3150]" data-bind-scroll-on-start="true"><p id="mntl-sc-block_1-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Proteins </strong>are very important molecules that are essential for all living organisms. By dry weight, proteins are the largest unit of cells. Proteins are involved in virtually all cell functions and a different type of protein is devoted to each role, with tasks ranging from general cellular support to cell signaling and locomotion. In total, there are seven types of proteins. </p> <div id="mntl-sc-block_2-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <div id="mntl-sc-block_3-0" class="comp mntl-sc-block reference-sc-block-callout mntl-sc-block-callout mntl-block theme-keytakeaways" data-tracking-id="mntl-sc-block-callout" data-tracking-container="true"><h3 id="mntl-sc-block-callout-heading_1-0" class="comp mntl-sc-block-callout-heading mntl-text-block">Proteins</h3> <div id="mntl-sc-block-callout-body_1-0" class="comp mntl-sc-block-callout-body mntl-text-block"><ul><li><strong>Proteins</strong> are biomolecules composed of amino acids that participate in nearly all cellular activities.</li><li>Occurring in the cytoplasm,<strong> translation </strong>is the process through which proteins are <strong>synthesized</strong>.</li><li>The typical protein is constructed from a single set of <strong>amino acids</strong>. Every protein is specially equipped for its function.</li><li class="ql-indent-1">Any protein in the human body can be created from permutations of only 20 amino acids.</li><li>There are seven types of proteins: <strong>antibodies, contractile proteins, enzymes, hormonal proteins, structural proteins, storage proteins</strong>, and <strong>transport proteins.</strong></li></ul></div></div> <span class="heading-toc" id="toc-protein-synthesis"></span><h2 id="mntl-sc-block_4-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Protein Synthesis </span> </h2> <p id="mntl-sc-block_5-0" class="comp mntl-sc-block mntl-sc-block-html"> Proteins are synthesized in the body through a process called <a href="https://www.thoughtco.com/protein-synthesis-translation-373400" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1"><strong>translation</strong></a>. Translation occurs in the <a href="https://www.thoughtco.com/cytoplasm-defined-373301" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">cytoplasm</a> and involves converting <a href="https://www.thoughtco.com/genetic-code-373449" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="3">genetic codes</a> into proteins. Genetic codes are assembled during DNA transcription, where DNA is decoded into RNA. Cell structures called <a href="https://www.thoughtco.com/ribosomes-meaning-373363" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="4">ribosomes</a> then help transcribe RNA into polypeptide chains that need to be modified to become functioning proteins. </p> <div id="mntl-sc-block_6-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_7-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Amino Acids and Polypeptide Chains </span> </h3> <p id="mntl-sc-block_8-0" class="comp mntl-sc-block mntl-sc-block-html"> <a href="https://www.thoughtco.com/amino-acid-373556" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1"><strong>Amino acids</strong></a> are the building blocks of all proteins, no matter their function. Proteins are typically a chain of 20 <a href="https://www.thoughtco.com/amino-acid-373556" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">amino acids</a>. The human body can use combinations of these same 20 amino acids to make any protein it needs. Most amino acids follow a structural template in which an alpha carbon is bonded to the following forms: </p> <div id="mntl-sc-block_9-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <ul id="mntl-sc-block_10-0" class="comp mntl-sc-block mntl-sc-block-html"> <li>A hydrogen atom (H)</li><li>A carboxyl group (-COOH)</li><li>An amino group (-NH2)</li><li>A "variable" group</li> </ul> <div id="mntl-sc-block_11-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_12-0" class="comp mntl-sc-block mntl-sc-block-html"> Across the different types of amino acids, the "variable" group is most responsible for variation as all of them have hydrogen, carboxyl group, and amino group bonds. </p> <div id="mntl-sc-block_13-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_14-0" class="comp mntl-sc-block mntl-sc-block-html"> Amino acids are joined through dehydration synthesis until they form peptide bonds. When a number of amino acids are linked together by these bonds, a polypeptide chain is formed. One or more polypeptide chains twisted into a 3-D shape forms a protein. </p> <div id="mntl-sc-block_15-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <span class="heading-toc" id="toc-protein-structure"></span><h2 id="mntl-sc-block_16-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Protein Structure </span> </h2> <p id="mntl-sc-block_17-0" class="comp mntl-sc-block mntl-sc-block-html"> The structure of a protein may be <strong>globular</strong> or <strong>fibrous</strong> depending on its particular role (every protein is specialized). Globular proteins are generally compact, soluble, and spherical in shape. Fibrous proteins are typically elongated and insoluble. Globular and fibrous proteins may exhibit one or more types of protein structures. </p> <div id="mntl-sc-block_18-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_19-0" class="comp mntl-sc-block mntl-sc-block-html"> There are <a href="https://www.thoughtco.com/protein-structure-373563" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">four structural levels</a> of protein: primary, secondary, tertiary, and quaternary. These levels determine the shape and function of a protein and are distinguished from one another by the degree of complexity in a polypeptide chain. The primary level is the most basic and rudimentary while the quaternary level describes sophisticated bonding. </p> <div id="mntl-sc-block_20-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_21-0" class="comp mntl-sc-block mntl-sc-block-html"> A single protein molecule may contain one or more of these protein structure levels and the structure and intricacy of a protein determine its function. Collagen, for example, has a super-coiled helical shape that is long, stringy, strong, and rope-like—collagen is great for providing support. Hemoglobin, on the other hand, is a globular protein that is folded and compact. Its spherical shape is useful for maneuvering through <a href="https://www.thoughtco.com/blood-vessels-373483" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">blood vessels</a>. </p> <div id="mntl-sc-block_22-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <span class="heading-toc" id="toc-types-of-proteins"></span><h2 id="mntl-sc-block_23-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Types of Proteins </span> </h2> <p id="mntl-sc-block_24-0" class="comp mntl-sc-block mntl-sc-block-html"> There is a total of seven different protein types under which all proteins fall. These include antibodies, contractile proteins, enzymes, hormonal proteins, structural proteins, storage proteins, and transport proteins. </p> <div id="mntl-sc-block_25-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_26-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Antibodies </span> </h3> <p id="mntl-sc-block_27-0" class="comp mntl-sc-block mntl-sc-block-html"> <a href="https://www.thoughtco.com/antibodies-373557" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1"><strong>Antibodies</strong></a> are specialized proteins that defend the body against antigens or foreign invaders. Their ability to travel through the <a href="https://www.thoughtco.com/facts-about-blood-373355" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">bloodstream</a> enables them to be utilized by the <a href="https://www.thoughtco.com/lymphocytes-definition-373382" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="3">immune system</a> to identify and defend against bacteria, viruses, and other foreign intruders in blood. One way antibodies counteract antigens is by immobilizing them so that they can be destroyed by <a href="https://www.thoughtco.com/white-blood-cell-373387" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="4">white blood cells</a>. </p> <div id="mntl-sc-block_28-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_29-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Contractile Proteins </span> </h3> <p id="mntl-sc-block_30-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Contractile proteins</strong> are responsible for <a href="https://www.thoughtco.com/muscle-tissue-anatomy-373195" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">muscle</a> contraction and movement. Examples of these proteins include actin and myosin. Eukaryotes tend to possess copious amounts of actin, which controls muscle contraction as well as cellular movement and division processes. Myosin powers the tasks carried out by actin by supplying it with energy. </p> <div id="mntl-sc-block_31-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_32-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Enzymes </span> </h3> <p id="mntl-sc-block_33-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Enzymes</strong> are proteins that facilitate and speed up biochemical reactions, which is why they are often referred to as catalysts. Notable enzymes include lactase and pepsin, proteins that are familiar for their roles in digestive medical conditions and specialty diets. Lactose intolerance is caused by a lactase deficiency, an enzyme that breaks down the sugar lactose found in milk. Pepsin is a digestive enzyme that works in the stomach to break down proteins in food—a shortage of this enzyme leads to indigestion. </p> <div id="mntl-sc-block_34-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_35-0" class="comp mntl-sc-block mntl-sc-block-html"> Other examples of digestive enzymes are those <a href="https://www.thoughtco.com/salivary-amylase-other-enzymes-in-saliva-4586549" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">present in saliva</a>: salivary amylase, salivary kallikrein, and lingual lipase all perform important biological functions. Salivary amylase is the primary enzyme found in saliva and it breaks down starch into sugar. </p> <div id="mntl-sc-block_36-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_37-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Hormonal Proteins </span> </h3> <p id="mntl-sc-block_38-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Hormonal proteins</strong> are messenger proteins that help coordinate certain bodily functions. Examples include insulin, oxytocin, and somatotropin. </p> <div id="mntl-sc-block_39-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_40-0" class="comp mntl-sc-block mntl-sc-block-html"> Insulin regulates glucose metabolism by controlling blood-sugar concentrations in the body, oxytocin stimulates contractions during childbirth, and somatotropin is a growth hormone that incites protein production in muscle cells. </p> <div id="mntl-sc-block_41-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_42-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Structural Proteins </span> </h3> <p id="mntl-sc-block_43-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Structural proteins</strong> are fibrous and stringy, this formation making them ideal for supporting various other proteins such as keratin, collagen, and elastin. </p> <div id="mntl-sc-block_44-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_45-0" class="comp mntl-sc-block mntl-sc-block-html"> Keratins strengthen protective coverings such as <a href="https://www.thoughtco.com/integumentary-system-373580" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">skin</a>, hair, quills, feathers, horns, and beaks. Collagen and elastin provide support to <a href="https://www.thoughtco.com/connective-tissue-anatomy-373207" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">connective tissues</a> like tendons and ligaments. </p> <div id="mntl-sc-block_46-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_47-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Storage Proteins </span> </h3> <p id="mntl-sc-block_48-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Storage proteins</strong> reserve amino acids for the body until ready for use. Examples of storage proteins include ovalbumin, which is found in egg whites, and casein, a milk-based protein. Ferritin is another protein that stores iron in the transport protein, hemoglobin. </p> <div id="mntl-sc-block_49-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <h3 id="mntl-sc-block_50-0" class="comp mntl-sc-block reference-sc-block-subheading mntl-sc-block-subheading"> <span class="mntl-sc-block-subheading__text"> Transport Proteins </span> </h3> <p id="mntl-sc-block_51-0" class="comp mntl-sc-block mntl-sc-block-html"> <strong>Transport proteins</strong> are carrier proteins that move molecules from one place to another in the body. Hemoglobin is one of these and is responsible for transporting oxygen through the blood via <a href="https://www.thoughtco.com/red-blood-cells-373487" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">red blood cells</a>. Cytochromes, another type of transport protein, operate in the <a href="https://www.thoughtco.com/cellular-respiration-process-373396" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">electron transport chain</a> as electron carrier proteins. </p></div> <div id="sources-and-citation_1-0" class="comp sources-and-citation mntl-block"><div id="citation-widget_1-0" class="comp citation-widget js-citation-widget" data-tracking-container="true"> <div class="citation-widget__container js-container"> <button class="citation-widget__button js-button"> <span class="citation-widget__cite-label">Cite this Article </span> <svg class="icon icon-cite citation-widget__icon-cite" > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-cite" href="#icon-cite"></use> </svg> </button> <div class="citation-widget__window js-window"> <svg class="icon icon-close citation-widget__icon-close js-icon-close" > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-close" href="#icon-close"></use> </svg> <div class="citation-widget__heading">Format</div> <a href="#" class="citation-widget__format-link citation-widget__format-link--active js-format-link">mla</a> <a href="#" class="citation-widget__format-link js-format-link">apa</a> <a href="#" class="citation-widget__format-link js-format-link">chicago</a> <div class="citation-widget__heading">Your Citation</div> <div class="citation-widget__content js-content"> <span class="citation-widget__citation citation-widget__citation--active js-active" data-citation-format="mla">Bailey, Regina. "Proteins in the Cell." ThoughtCo, Apr. 5, 2023, thoughtco.com/protein-function-373550.</span> <span class="citation-widget__citation" data-citation-format="apa">Bailey, Regina. (2023, April 5). Proteins in the Cell. Retrieved from https://www.thoughtco.com/protein-function-373550</span> <span class="citation-widget__citation" data-citation-format="chicago">Bailey, Regina. "Proteins in the Cell." ThoughtCo. https://www.thoughtco.com/protein-function-373550 (accessed February 18, 2025).</span> </div> <div class="citation-widget__copy-container"> <button class="citation-widget__copy-button js-copy-button"> <div class="citation-widget__copy-wrapper"> <svg class="icon icon-checkmark citation-widget__icon-checkmark" > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-checkmark" href="#icon-checkmark"></use> </svg> <span class="citation-widget__copy-label js-copy-label">copy citation</span> </div> </button> </div> </div> </div> </div></div></div> </div><div class="loc article-right-rail"><div id="mm-ads-right-rail_1-0" class="comp mm-ads-right-rail mntl-block"><div id="sc-billboard-group_1-0" class="comp sc-billboard-group mntl-block js-scads-inline-content"><div id="mntl-block_2-0" class="comp mntl-block"><div id="ref-billboard1-sticky-dynamic_1-0" class="comp ref-billboard1-sticky-dynamic mntl-block"><div id="mm-ads-sc-sticky-square-ad_1-0" class="comp 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