Energy Metabolism II | Biology

<!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>Energy Metabolism II | Biology | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/biology/2/energy-metabolism-ii/225"> <meta name="description" content="ATP is the main energy currency of living cells. This module answers the question of how most ATP is generated. A look at two important compounds, NADH and FADH<sub>2</sub>, reveals their important role in the production of ATP. The module explains the workings of the electron transport chain, which provides high-energy electrons to fuel the ATP-producing process called oxidative phosphorylation."> <meta name="keywords" content="ATP, adenosine triphosphate, cell energy, glucose, electron transport chain"> <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/energy-metabolism-ii/225" }, "name": "Energy Metabolism II", "headline": "Energy Metabolism II: The Generation of ATP", "author": [ { "@type": "Person", "name": "David Warmflash, MD" } , { "@type": "Person", "name": "Nathan H Lents, Ph.D." }], "datePublished": "2016-04-27 04:29:23", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_225-23061209062951.jpeg", "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": "ATP is the main energy currency of living cells. This module answers the question of how most ATP is generated. A look at two important compounds, NADH and FADH<sub>2</sub>, reveals their important role in the production of ATP. The module explains the workings of the electron transport chain, which provides high-energy electrons to fuel the ATP-producing process called oxidative phosphorylation.", "keywords": "ATP, adenosine triphosphate, cell energy, glucose, electron transport chain", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2016"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/biology/2/energy-metabolism-ii/225"> <meta property="og:title" content="Energy Metabolism II | Biology | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="ATP is the main energy currency of living cells. This module answers the question of how most ATP is generated. A look at two important compounds, NADH and FADH<sub>2</sub>, reveals their important role in the production of ATP. The module explains the workings of the electron transport chain, which provides high-energy electrons to fuel the ATP-producing process called oxidative phosphorylation."> <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="preload" href="https://fonts.gstatic.com"> <link rel="preload" href="https://fonts.googleapis.com/css2?family=Open+Sans:ital,wght@0,400;0,700;1,400;1,700&family=Schoolbell&display=swap"> <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" 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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><a href="/en/library/biology/2/lipids/207">Lipids</a></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 class="current">Energy Metabolism II</li> <li><a href="/en/library/biology/2/photosynthesis-i/192">Photosynthesis I</a></li> </ul> </div> <button 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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 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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"> <article class="container wide module"> <header class="grid grid--sidebar-right module__header"> <div class="module__header__title"> <span class="subcategory"> <strong><em>Energy in Living Systems</em></strong> </span> <h1>Energy Metabolism II: <sub><em>The Generation of ATP</em></sub></h1> <p class="byline">by David Warmflash, MD, Nathan H Lents, Ph.D.</p> <nav class="module__header__tabs"> <ul class="tabs-nav tabs-nav--horizontal library"> <li> <a href="/en/library/biology/2/energy-metabolism-ii/225/reading" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/biology/2/energy-metabolism-ii/225/quiz">Quiz</a> </li> <li> <a href="/en/library/biology/2/energy-metabolism-ii/225/resources">Teach with this</a> </li> </ul> </nav> </div> </header> <hr class="divider"/>   <div class="grid grid--sidebar-right grid--divider"> <div class="order-2 order-1--lg module__main"> <div class="narrow margin-x-auto margin-y-5"> <div class="accordion margin-bottom-5">  <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 the energy in chemical compounds is found in tiny electrons? The electron transport chain is like an assembly line inside of cells that harnesses high-energy electrons so they can be used to make ATP, the energy that organisms need to survive. When Peter Mitchell proposed the way that ATP is made inside cells, other scientists made fun of him – until he was eventually proved correct and won the Nobel Prize in Chemistry.</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"> <p><ul class="bulleted"> <li>Adenosine triphosphate (ATP) is the main energy currency of the cell. It is generated from a similar compound, ADP, using energy harnessed from cellular fuels, such as sugars, fats, and proteins.</li> <li>The amount of ATP generated directly during glycolysis (the breakdown of the sugar glucose) is small compared with amount of energy contained within glucose. </li> <li>The energy held by ATP and other energy-holding chemical compounds is contained in electrons. By moving electrons, different molecules move energy around the cell.</li> <li>Two specialized energy currency compounds, NADH and FADH<sub>2</sub>, are vital to the movement of high-energy electrons from cellular fuels like glucose to an assembly-line system of enzymes called the electron transport chain.</li> <li>Located inside mitochondria, the electron transport chain harnesses energy from NADH and FADH<sub>2</sub> to power a process called oxidative phosphorylation, which generates large amounts of ATP. Oxidative phosphorylation requires oxygen.</li> </ul></p> </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/membrane">membrane </a></dt> <dd> a thin layer of tissue that forms a boundary. </dd> <dt>oxidized </dt> <dd> the resulting state of an atom or molecule that has lost electrons. </dd> <dt><a href="/en/glossary/view/reaction">reaction </a></dt> <dd> a chemical change that happens when two or more atoms or molecules come into contact with each other. </dd> <dt>reduced </dt> <dd> the resulting state of an atom or molecule that has gained electrons.</dd> </dl> </div> </div> </div> <hr class="border-color-dark" /> <section> <div class="container narrow"> <p>The discovery of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark>, glycolysis, and the Krebs cycle during the first half of the 20th century went a long way in answering the question of how <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> from food <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>, such as <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark>, is harnessed by 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">cell</mark>. But a huge question remained –namely, how is the bulk of the energy of food molecules converted to ATP?</p> <p>Chemical <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 contained in <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>. Since electrons can move between different <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 energy can travel as well. By harnessing high-energy electrons from each <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark> molecule, glycolysis generates <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> from a precursor molecule called ADP (Figure 1). Similarly, the Krebs cycle and other energy pathways also generate <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark>, which serves as a kind of energy currency for 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">cell</mark>.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_8589.jpg"> <img src="/img/library/modules/mid225/Image/VLObject-8589-150714090706.jpg" alt="Figure 1: A diagram of the glycolysis process that occurs in the cytoplasm of a cell." /> </button> <figcaption> <p><strong>Figure 1</strong>: A diagram of the glycolysis process that occurs in the cytoplasm of a cell.</p> <span class="credit">image ©RegisFrey</span> </figcaption> </figure> </div> <p>Figuring out the <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> generation <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> took decades and involved many researchers, but it was off to a good start by the 1930s. At that time, Sir <mark class="term" data-term="Hans Adolf Krebs" data-term-def="1900–1981). One of thousands of scientists who fled Germany because of their Jewish heritage when the Nazis came to power, Krebs&hellip;" data-term-url="/en/glossary/view/Krebs%2C+Hans+Adolf/10184">Hans Adolf Krebs</mark> was beginning 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>. Using newly available instruments, such as the manometer (developed by Krebs’ mentor, Otto Warburg, one of the giants of biochemistry of that era, see Figure 2), biochemists were able to hone in on specific quantities of <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark> that are made in different biochemical <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">reactions</mark>. They found that glycolysis (the splitting of a <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</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> into two molecules of pyruvate) generates two or three molecules of ATP for each molecule of glucose that is consumed. The Krebs cycle also generates two ATP molecules for each glucose molecule that is broken down. Additionally, one other reaction – the breakdown of pyruvate to produce acetate that goes into the Krebs cycle – generates two ATP molecules for each glucose molecule that is consumed.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_9587.jpg"> <img src="/img/library/modules/mid225/Image/VLObject-9587-160425010458.jpg" alt="Figure 2: Dr. Otto Warburg and his manometer. The instrument, adapted from devices that measure gases dissolved in blood, determines the rate at which living cells produce oxygen." /> </button> <figcaption> <p><strong>Figure 2</strong>: Dr. Otto Warburg and his manometer. The instrument, adapted from devices that measure gases dissolved in blood, determines the rate at which living cells produce oxygen.</p> <span class="credit">image ©History of Medicine (NLM)</span> </figcaption> </figure> </div> <p>Adding up the <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</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">molecules</mark> generated for each <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark> molecule during glycolysis (2-3 ATP), the Krebs cycle (2 ATP), and the conversion of pyruvate to acetate (2 ATP) yields 6-7 <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark> molecules per glucose molecule. However, using the Warburg manometer in slightly different <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">experiments</mark> (mostly involving liver and muscle tissue), Krebs and his colleagues realized that more than 6-7 ATP molecules are actually generated from each molecule of glucose, a great deal more. Their measurements told them that each glucose molecule actually generates well over 30 ATP molecules, provided that oxygen is available to 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">cell</mark>. </p><p>To mid-20th century biochemists, the discrepancy between 30 <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> of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> generated by 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">cell</mark> and just 6-7 <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark> molecules generated by known <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">reactions</mark> could mean only one thing. Clearly, the remainder of the ATP must be generated indirectly from other chemical <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> generated during glycolysis, the Krebs cycle, and the conversion of pyruvate to acetate.</p><p>These “other chemical products” are nicotinamide adenine dinucleotide (NADH) and FADH<sub>2</sub>. For each <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</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> consumed, Krebs worked out that his cycle generated six molecules of NADH and two molecules of FADH<sub>2</sub> (Figure 3). Additionally, it was known that NADH also was produced during glycolysis and during the conversion of pyruvate to acetate. Scientists also observed that NADH and FADH<sub>2</sub> are produced during the breakdown of fats (a <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> called beta oxidation). Just like <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark>, both NADH and FADH<sub>2</sub> seemed to be all over 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">cell</mark> and connected with <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> <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">reactions</mark>. This was the state of knowledge on cellular energy during the late 1940s, when Krebs was tweaking the details of his famous cycle.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_9588.gif"> <img src="/img/library/modules/mid225/Image/VLObject-9588-160425020457.gif" alt="Figure 3: The Krebs Cycle within the mitochondria, showing the generation of NADH and FADH2 molecules." /> </button> <figcaption> <p><strong>Figure 3</strong>: The Krebs Cycle within the mitochondria, showing the generation of NADH and FADH<sub>2</sub> molecules.</p> <span class="credit">image ©RegisFrey</span> </figcaption> </figure> </div> <p>But as for the specific role of NADH and FADH<sub>2</sub> – how 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">cell</mark> could use them to obtain <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> – that was a mystery. It was clear that they were carrying the bulk of the energy extracted from <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark>, fats, and other body fuels, but it was not clear how that energy was harnessed to produce <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark>. </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 class="" name="cc9183"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Each molecule of glucose generates ______ molecules of ATP.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-9183-0-option-a" name="quiz-option-9183" type="radio" value="6-7" > <span class="option__label"> <span class="screen-reader-only">a.</span> 6-7 </span> </label> <span class="quiz__response" id="response-9183-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-9183-1-option-b" name="quiz-option-9183" type="radio" value="more than 30" > <span class="option__label"> <span class="screen-reader-only">b.</span> more than 30 </span> </label> <span class="quiz__response" id="response-9183-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> <p><section id="toc_1" class=""> <h2>Accounting for the rest of the ATP</h2></p> <p>At the midpoint of the 20th century, Krebs and other biochemists knew that NADH and FADH<sub>2</sub> disappear after their production and transform into slightly different <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>. Using very straightforward chemistry techniques, they saw that both NADH and FADH<sub>2</sub> undergo a chemical <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> called oxidation. In the oxidation <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>, NADH is converted, or oxidized, to a <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> called NAD+ and FADH<sub>2</sub> is converted (oxidized) to a compound called FADH+. In becoming NAD+ and FADH+, NADH and FADH<sub>2</sub> each give up one 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">atom</mark> and two <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>. </p><p>Thus, biochemists began describing NADH and FADH<sub>2</sub> as carriers of a sort: carriers of <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 their oxidized forms, NAD+ and FADH+, the electron carriers contain less <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> than they do in what’s called their reduced forms, NADH and FADH<sub>2</sub>. The reduced forms of 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> are more energetic than the oxidized forms, because the electrons physically hold the energy. By liberating a pair of electrons, NADH and FADH<sub>2</sub> return to their oxidized forms. That much was clear to Krebs, but this raised the question of what happens to the electrons. They don’t just disappear into nothingness. Clearly, their energy must be used to generate all the rest of the <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> that is not made directly during glycolysis and the other <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">reactions</mark>.</p><p>Figuring out exactly how this worked required a new researcher, and his name was Peter Mitchell. In the 1960s, Mitchell introduced an idea that he called “chemiosmosis.” It explains how 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">cell</mark> harnesses <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> from <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>, and it depends on another phenomenon called <em>electron transport</em>, which had to be discovered first, by other researchers.</p><p>Born in England, September 29, 1920, Mitchell showed an interest in science throughout childhood and entered Cambridge University in 1939 at age 19. There, he was influenced especially by two instructors: biochemist Ernest Baldwin and nerve physiology instructor Edgar Adrian. As a child and throughout most of his undergraduate career, Mitchell often did not perform well on tests, but he improved enough for admission to graduate school where he pursued biochemistry.</p><p>As a graduate student, Mitchell conceived of numerous, novel <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">experiments</mark> but often failed to complete them. Generally, it was his assistant, Jennifer Moyle, who completed the needed laboratory work. On top of that, his first PhD thesis idea was rejected and he was directed to spend an additional three years researching penicillin, a topic that didn’t excite him very much. Mitchell lacked the patience for the nitty-gritty work that goes along with experimental science. But he put in the needed laboratory work to earn his PhD and later to show the world that his <mark class="term" data-term="chemiosmosis" data-term-def="The movement of ions along an electrochemical gradient through a membrane. Usually, the term is applied in connection with a proton&hellip;" data-term-url="/en/glossary/view/chemiosmosis/10174">chemiosmosis</mark> idea was correct.</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 class="" name="cc9190"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Which form of the molecules have more energy?</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-9190-0-option-a" name="quiz-option-9190" type="radio" value="NADH and FADH<sub>2</sub> (reduced form)" > <span class="option__label"> <span class="screen-reader-only">a.</span> NADH and FADH<sub>2</sub> (reduced form) </span> </label> <span class="quiz__response" id="response-9190-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-9190-1-option-b" name="quiz-option-9190" type="radio" value="NAD+ and FADH+ (oxidized form)" > <span class="option__label"> <span class="screen-reader-only">b.</span> NAD+ and FADH+ (oxidized form) </span> </label> <span class="quiz__response" id="response-9190-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_2"> <h2>The fate of the high-energy electrons</h2><p>Tracking the pathways of NADH and FADH<sub>2</sub> over the next few years led to the discovery that these two <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> were actually <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> carriers. Like <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark>, they were a kind 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> currency, but the currency of NADH and FADH<sub>2</sub> is less versatile compared with that of <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark>. Imagine ATP as a universal energy currency for 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">cell</mark>; it can be used in many different ways, and thus each <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> of ATP can be likened to a dollar bill. In contrast NADH and FADH<sub>2</sub> can be likened to a store-specific gift card. They carry energy value, but that value can be used only for a special purpose. That purpose is the generation of ATP, and the way that ATP is generated begins with the high-energy electrons that NADH and FADH<sub>2</sub> acquired during glycolysis, the Krebs cycle, and other pathways.</p><p>Once scientists realized that <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> could be carried through 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">cell</mark> by transferring <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> between different <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>, researchers began contemplating how this could happen. Harnessing the energy from the high-energy electrons of NADH and FADH<sub>2</sub> occurs in two interconnected processes: electron transport and oxidative phosphorylation.</p><p>In the 1930s, two Soviet researchers, Vladimir Aleksandrovitch Belitser and Elena Tsybakova, identified the movement of <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> through a series of special <mark class="term" data-term="enzyme" data-term-def="Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly&hellip;" data-term-url="/en/glossary/view/enzyme/1595">enzymes</mark>. This transfer of electrons from one enzyme <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> to another was called “electron transport.” In 1953, Dutch researcher Edward Charles Slater identified the various enzymes of the chain and began researching how they operate. The enzymes are embedded in the inner of two <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> that surround each mitochondrion, the powerhouse <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelle</mark> of <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <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>. They are also in the membranes of certain microorganisms. Within the membrane, the enzymes are lined up, forming a chain, known as the electron transport chain (ETC) (Figure 4). Like NADH and FADH<sub>2</sub>, each electron carrier enzyme of the ETC is capable of accepting electrons from other molecules, holding those electrons temporarily, and then releasing them to a different electron carrier.</p><p>Arriving at the <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">membrane</mark> of each mitochondrion, both NADH and FADH<sub>2</sub> easily unload their high-energy <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> to the ETC. In addition to being lined up, the electron carriers of the mitochondrial ETC are arranged into four groups known as complexes. Today, we know that NADH “drops off” its electrons at complex I, while FADH<sub>2</sub> drops off its electrons at complex II. This is because the electrons donated by NADH actually have more <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> than the electrons donated by FADH<sub>2</sub>. NADH is like a high-energy package; whereas FADH<sub>2</sub> is like a lower energy package.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_9589.gif"> <img src="/img/library/modules/mid225/Image/VLObject-9589-160425030413.gif" alt="Figure 4: At the barrier to the intermembrane space of the mitochondria exists the Electron Transport Chain (ETC), where electrons move through a series of special enzymes. Both NADH and FADH2 unload their high-energy electrons to the ETC." /> </button> <figcaption> <p><strong>Figure 4</strong>: At the barrier to the intermembrane space of the mitochondria exists the Electron Transport Chain (ETC), where electrons move through a series of special enzymes. Both NADH and FADH<sub>2</sub> unload their high-energy electrons to the ETC.</p> <span class="credit">image ©RegisFrey</span> </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 class="" name="cc9196"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Electrons can be transferred from one enzyme molecule to another.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-9196-0-option-a" name="quiz-option-9196" type="radio" value="True" > <span class="option__label"> <span class="screen-reader-only">a.</span> True </span> </label> <span class="quiz__response" id="response-9196-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-9196-1-option-b" name="quiz-option-9196" type="radio" value="False" > <span class="option__label"> <span class="screen-reader-only">b.</span> False </span> </label> <span class="quiz__response" id="response-9196-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_3"> <h2>ATP and oxygen</h2><p>By the mid 20th century, biochemists had an idea that <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> give off their <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> gradually while moving through the ETC. The generation of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> from ADP is called “phosphorylation,” which refers to the addition of a group of <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> known chemically as a phosphate (PO<sub>4</sub><sup>3-</sup>) group. Biochemists observed that electrons move through the ETC as ADP is phosphorylated into <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark>. Since it was observed to happen in the presence of oxygen, researchers began using the term “oxidative phosphorylation” to describe the generation of ATP connected to electron transport. This contrasts with ATP production that occurs directly in biochemical <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">reactions</mark>, such as glycolysis and the Krebs cycle, which is called “substrate level phosphorylation.”</p><p>In certain types of human <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>, glycolysis (but not the breakdown of fats) can proceed in the absence of oxygen. This means that substrate level phosphorylation of glycolysis can occur in the absence of oxygen. This is called anaerobic glycolysis and when it happens, small amounts of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> are produced along with pyruvate. This keeps cells alive and working, but there are consequences. Without oxygen powering the ETC to draw the high-energy <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> from NADH, the cell needs a different way to oxidize NADH back to NAD+. That’s because the supply of NAD+ is limited. If NAD+ runs out because it has all been converted to NADH, glycolysis will stop. </p><p>To solve the problem, when oxygen supplies are low, 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">cell</mark> converts pyruvate (made during glycolysis) into lactic <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>. In being converted to lactic acid, pyruvate receives <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> from NADH. Thus, NADH is oxidized, converted back to NAD+, which then is available to glycolysis. But it’s only a temporary solution. During anaerobic glycolysis in muscle cells, lactic acid builds up, causing pain and <mark class="term" data-term="cramp" data-term-def="A sustained and involuntary contraction of the muscle." data-term-url="/en/glossary/view/cramp/7384">cramps</mark>. That’s why you feel pain if you start exercising too quickly. But as you exercise more, oxidative phosphorylation kicks in gradually as <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> start working harder. NADH from glycolysis moves into mitochondria and delivers electrons to the ETC. Large amounts of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> are then generated. By giving up electrons, NADH is converted back to NAD+, which then is available to glycolysis, so the production of lactic acid stops.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid225/Image/VLObject-9590-160425040413.png" alt="Figure 5: During exercise, muscle cells build up lactic acid during anaerobic glycolysis, leading to pain and cramps." /> </button> <figcaption> <p><strong>Figure 5</strong>: During exercise, muscle cells build up lactic acid during anaerobic glycolysis, leading to pain and cramps.</p> <span class="credit">image ©Jan-Otto, iStockPhoto</span> </figcaption> </figure> </div> <p>The big question in the mid 20th century, though, was how does oxidative phosphorylation work? How is <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> of 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 are delivered to the ETC harnessed for the production of ATP? That’s the question that Peter Mitchell set out to answer.</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 class="" name="cc9202"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Lactic acid is produced when oxygen is</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-9202-0-option-a" name="quiz-option-9202" type="radio" value="abundant." > <span class="option__label"> <span class="screen-reader-only">a.</span> abundant. </span> </label> <span class="quiz__response" id="response-9202-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-9202-1-option-b" name="quiz-option-9202" type="radio" value="scarce." > <span class="option__label"> <span class="screen-reader-only">b.</span> scarce. </span> </label> <span class="quiz__response" id="response-9202-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>Transferring the energy</h2><p>By the early 1960s, a chemist named Robert Joseph Paton Williams proposed a new idea: The <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> from <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> delivered to the ETC is converted to <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> using <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">protons</mark> (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> without their electrons) as intermediates. To explain how the proton idea might operate, exploring the possible ways protons act as intermediates for <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark> production, Williams proposed a very complex chemical mechanism. At the same time as Williams developed these ideas, however, Mitchell also independently proposed that protons couple electron transport with ATP production, but through an entirely different mechanism. Mitchell came up with something simpler called the “proton motive force.”</p><p>Imagine blowing up a balloon - forcing air into the balloon stores up <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>. And, once forced into the balloon, air will flow out through any hole with great force. Similarly, Mitchell imagined energy being stored, not with air, but with <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">protons</mark> forced into the space between the two <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> of a mitochondrion, using energy obtained during <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> transport. If there is an opening in the membrane, then the protons will stream out, like air from a balloon, with force. In chemistry, this is known as a proton gradient, but Mitchell used the term proton motive force, because he imagined <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> using it for power.</p><p>Mitchell used the term chemiosmosis” to describe the overall mechanism of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> generation that he imagined taking place within <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark>, and within microorganisms that thrive in oxygen. He hypothesized his <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">proton</mark> motive force being harnessed by <mark class="term" data-term="enzyme" data-term-def="Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly&hellip;" data-term-url="/en/glossary/view/enzyme/1595">enzymes</mark> to convert ADP to <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark>, and also to power other <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> processes. For instance, in <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> (organelles that use sunlight to make food in cells of plants and certain other eukaryotes) 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>, he imagined the proton gradient transferring sunlight <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 energize various <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>. He also hypothesized proton gradients being used to transform chemical energy into <mark class="term" data-term="mechanical" data-term-def="Involving physical force or motion." data-term-url="/en/glossary/view/mechanical/8516">mechanical</mark> energy. Many bacteria and other microorganisms move around with a tail like structure called a flagellum, and Mitchell imagined the tiny protons causing a flagellum to move.</p></section> <section id="toc_5"> <h2>Mitchell: An unconventional thinker</h2><p>When Mitchell proposed <mark class="term" data-term="chemiosmosis" data-term-def="The movement of ions along an electrochemical gradient through a membrane. Usually, the term is applied in connection with a proton&hellip;" data-term-url="/en/glossary/view/chemiosmosis/10174">chemiosmosis</mark> in 1961, his colleagues thought the idea was crazy. Mocking the idea of the <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">proton</mark> motive force, which Mitchell abbreviated PMF, his colleagues joked that PMF stood for the “Peter Mitchell Force.” This was mostly because Mitchell lacked <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> to support the idea at the time, but also because he looked and acted rather unorthodox.</p><p>Holding fast to <mark class="term" data-term="chemiosmosis" data-term-def="The movement of ions along an electrochemical gradient through a membrane. Usually, the term is applied in connection with a proton&hellip;" data-term-url="/en/glossary/view/chemiosmosis/10174">chemiosmosis</mark> and ignoring those who mocked him, Mitchell did the needed lab work and also watched carefully for discoveries by others that could be relevant to his idea. During the 1960s and 1970s, such relevant discoveries revolved around how the ETC could transfer <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> from <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> into a gradient of <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">protons</mark>. While the physics is beyond the scope of this module, the take-home message is this: As electrons move along the chain, giving up their energy gradually, special <mark class="term" data-term="enzyme" data-term-def="Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly&hellip;" data-term-url="/en/glossary/view/enzyme/1595">enzymes</mark> take that energy and literally pump protons into the intermembrane space (see Figure 4). Recall that the ETC enzymes are lined up, embedded in the <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">membrane</mark>. As electrons move along the ETC in a conveyor belt fashion, protons are pumped in a direction perpendicular to the movement of the electrons.</p><p>The other <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> relevant for Mitchell revolved around an <mark class="term" data-term="enzyme" data-term-def="Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly&hellip;" data-term-url="/en/glossary/view/enzyme/1595">enzyme</mark> called <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> synthase. Located in the inner mitochondrial <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">membrane</mark>, this enzyme proved to be a key component since it acts as a doorway for <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">protons</mark> which want to move out from between the two membranes (Figure 6). </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_9591.jpg"> <img src="/img/library/modules/mid225/Image/VLObject-9591-160427040428.jpg" alt="Figure 6: The world's smallest motor, the enzyme ATP synthase, generates energy for the cell." /> </button> <figcaption> <p><strong>Figure 6</strong>: The world's smallest motor, the enzyme ATP synthase, generates energy for the cell.</p> <span class="credit">image ©National Institute of General Medical Sciences</span> </figcaption> </figure> </div> <p>Thinking of the balloon analogy from earlier, imagine if there was a wind turbine capturing <mark class="term" data-term="mechanical" data-term-def="Involving physical force or motion." data-term-url="/en/glossary/view/mechanical/8516">mechanical</mark> <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> from the air moving out of the balloon. Like a mini-turbine, the <mark class="term" data-term="enzyme" data-term-def="Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly&hellip;" data-term-url="/en/glossary/view/enzyme/1595">enzyme</mark> <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> synthase harnesses the power of the <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">protons</mark> streaming out from between the <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 uses the energy to generate <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark>. Vindicated due to the growing understanding of ATP synthase and other discoveries related to membranes, Mitchell was awarded 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 Chemistry in 1978.</p> </div> </section> <hr class="border-color-dark" /> <footer class="module__footer"> <p class="citation"> <em> David Warmflash, MD, Nathan H Lents, Ph.D. “Energy Metabolism II” Visionlearning Vol. BIO-4 (5), 2016. </em> </p>  <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/Carbohydrates/61"> <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_61-23061209062220.jpeg" alt="Carbohydrates"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Carbohydrates: <em>Simple sugars and complex carbohydrates</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Biology/2/Photosynthesis-I/192"> <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_192-23061209063006.jpg" alt="Photosynthesis I"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Photosynthesis I: <em>Harnessing the energy of the sun</em> </h2> </div> </article> </a> </li> </ul> </div> </footer> </div>   </div>  <div class="order-1 order-2--lg module__tools"> <div class="narrow margin-x-auto position-sticky-top font-size-md"> <div class="padding-2 border-radius box-shadow-1--lg"> <div class="tabs" role="tablist"> <nav> <button class="button button--icon-label" id="tab-button-in-this-module" aria-label="Table of Contents" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="icon icon-list" aria-hidden="true"></span> <span class="button__text">Contents</span> </button> <button class="button button--icon-label" id="tab-button-toggle-terms" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="icon icon-glossary-highlight"></span> <span class="button__text">Glossary Terms</span> </button> </nav> <hr class="divider" /> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <p class="font-weight-bold margin-bottom-1"> Table of Contents </p> <div class="table-of-contents" id="module-toc"> <ul> <li><a href="/en/library/biology/2/energy-metabolism-ii/225#toc_1">Accounting for the rest of the ATP</a> </li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225#toc_2">The fate of the high-energy electrons</a> </li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225#toc_3">ATP and oxygen</a> </li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225#toc_4">Transferring the energy</a> </li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225#toc_5">Mitchell: An unconventional thinker</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. 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