{"id":25627,"date":"2025-06-19T05:52:02","date_gmt":"2025-06-19T05:52:02","guid":{"rendered":"https:\/\/gaviki.com\/blog\/?p=25627"},"modified":"2025-06-19T05:52:04","modified_gmt":"2025-06-19T05:52:04","slug":"redox-active-species-along-the-electron-transport-chain-have-reduction-potentials-between-the-values-of-the-nad-nadh-redox-couple-320-mv-and-the-oxygen-water-redox-couple-818-mv","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/redox-active-species-along-the-electron-transport-chain-have-reduction-potentials-between-the-values-of-the-nad-nadh-redox-couple-320-mv-and-the-oxygen-water-redox-couple-818-mv\/","title":{"rendered":"Redox active species along the electron transport chain have reduction potentials between the values of the NAD+\/NADH redox couple (-320 mV) and the oxygen\/water redox couple (+818 mV)."},"content":{"rendered":"\n<p>Redox active species along the electron transport chain have reduction potentials between the values of the NAD+\/NADH redox couple (-320 mV) and the oxygen\/water redox couple (+818 mV). Electrons can thereby move down the energy scale toward progressively more positive reduction potentials! Calculate the free energy change \u00ce\u201dG\u00c2\u00ba&#8217; for the final outcome of the NADH re-oxidation via the electron transport chain. Use the following information: Overall reaction: NADH + H+ + \u00c2\u00bd O2 \u00e2\u2020\u2019 NAD+ + H2O Standard reduction potential for NAD+\/NADH redox couple: NAD+ + 2H+ + 2e- \u00e2\u2020\u2019 NADH + H+ E0&#8242; = -0.32 V Standard reduction potential for oxygen\/water redox couple: \u00c2\u00bd O2 + 2H+ + 2e- \u00e2\u2020\u2019 H2O E0&#8242; = +0.816 V The picture below provides \u00ce\u201dE0&#8242; values and \u00ce\u201dG0&#8242; values for segments within the electron transport chain. Demonstrate how the \u00ce\u201dE0&#8242; and \u00ce\u201dG0&#8242; values were calculated for complexes I, III, and IV. What \u00ce\u201dE0&#8242; and \u00ce\u201dG0&#8242; value would you get for complex II<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-light-green-cyan-color\">The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n<p>To calculate the <strong>standard free energy change (\u0394G\u00b0&#8217;)<\/strong> for redox reactions in the electron transport chain, we use the following relationship:\u0394G\u00b0\u2032=\u2212nF\u0394E\u00b0\u2032\\Delta G\u00b0&#8217; = -nF\\Delta E\u00b0&#8217;\u0394G\u00b0\u2032=\u2212nF\u0394E\u00b0\u2032<\/p>\n\n\n\n<p>Where:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>n<\/strong> is the number of electrons transferred (in this case, 2),<\/li>\n\n\n\n<li><strong>F<\/strong> is Faraday&#8217;s constant (96.485 kJ\/V\u00b7mol),<\/li>\n\n\n\n<li><strong>\u0394E\u00b0&#8217;<\/strong> is the difference in standard reduction potentials between the electron acceptor and donor.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Step 1: Overall NADH Oxidation via Electron Transport Chain<\/strong><\/h3>\n\n\n\n<p>Overall redox reaction:NADH+H++12O2\u2192NAD++H2O\\text{NADH} + \\text{H}^+ + \\frac{1}{2} \\text{O}_2 \\rightarrow \\text{NAD}^+ + \\text{H}_2\\text{O}NADH+H++21\u200bO2\u200b\u2192NAD++H2\u200bO<\/p>\n\n\n\n<p>Standard reduction potentials:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NAD\u207a\/NADH: <strong>-0.320 V<\/strong><\/li>\n\n\n\n<li>O\u2082\/H\u2082O: <strong>+0.816 V<\/strong><\/li>\n<\/ul>\n\n\n\n<p>Now calculate \u0394E\u00b0&#8217;:\u0394E\u00b0\u2032=E\u00b0acceptor\u2032\u2212E\u00b0donor\u2032=0.816\u2009V\u2212(\u22120.320\u2009V)=1.136\u2009V\\Delta E\u00b0&#8217; = E\u00b0&#8217;_{\\text{acceptor}} &#8211; E\u00b0&#8217;_{\\text{donor}} = 0.816\\,\\text{V} &#8211; (-0.320\\,\\text{V}) = 1.136\\,\\text{V}\u0394E\u00b0\u2032=E\u00b0acceptor\u2032\u200b\u2212E\u00b0donor\u2032\u200b=0.816V\u2212(\u22120.320V)=1.136V<\/p>\n\n\n\n<p>Calculate \u0394G\u00b0&#8217;:\u0394G\u00b0\u2032=\u2212nF\u0394E\u00b0\u2032=\u2212(2)(96.485\u2009kJ\/V\\cdotpmol)(1.136\u2009V)\u2248\u2212219.3\u2009kJ\/mol\\Delta G\u00b0&#8217; = -nF\\Delta E\u00b0&#8217; = -(2)(96.485\\,\\text{kJ\/V\u00b7mol})(1.136\\,\\text{V}) \\approx -219.3\\,\\text{kJ\/mol}\u0394G\u00b0\u2032=\u2212nF\u0394E\u00b0\u2032=\u2212(2)(96.485kJ\/V\\cdotpmol)(1.136V)\u2248\u2212219.3kJ\/mol<\/p>\n\n\n\n<p>So the <strong>standard free energy change<\/strong> for NADH re-oxidation through the ETC is approximately <strong>-219.3 kJ\/mol<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Step 2: Calculating \u0394E\u00b0&#8217; and \u0394G\u00b0&#8217; for Complexes<\/strong><\/h3>\n\n\n\n<p>You would use the same method as above for each complex:<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Example: Complex I<\/strong><\/h4>\n\n\n\n<p>Suppose Complex I transfers electrons from NADH to ubiquinone (Q), with:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NAD\u207a\/NADH = -0.320 V<\/li>\n\n\n\n<li>Q\/QH\u2082 = +0.045 V<\/li>\n<\/ul>\n\n\n\n<p>\u0394E\u00b0\u2032=0.045\u2212(\u22120.320)=0.365\u2009V\\Delta E\u00b0&#8217; = 0.045 &#8211; (-0.320) = 0.365\\,\\text{V}\u0394E\u00b0\u2032=0.045\u2212(\u22120.320)=0.365V\u0394G\u00b0\u2032=\u2212(2)(96.485)(0.365)\u2248\u221270.4\u2009kJ\/mol\\Delta G\u00b0&#8217; = -(2)(96.485)(0.365) \\approx -70.4\\,\\text{kJ\/mol}\u0394G\u00b0\u2032=\u2212(2)(96.485)(0.365)\u2248\u221270.4kJ\/mol<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Complex II<\/strong><\/h4>\n\n\n\n<p>Electrons are transferred from FADH\u2082 (E\u00b0&#8217; = -0.03 V) to ubiquinone (Q\/QH\u2082 = +0.045 V):\u0394E\u00b0\u2032=0.045\u2212(\u22120.03)=0.075\u2009V\\Delta E\u00b0&#8217; = 0.045 &#8211; (-0.03) = 0.075\\,\\text{V}\u0394E\u00b0\u2032=0.045\u2212(\u22120.03)=0.075V\u0394G\u00b0\u2032=\u2212(2)(96.485)(0.075)\u2248\u221214.5\u2009kJ\/mol\\Delta G\u00b0&#8217; = -(2)(96.485)(0.075) \\approx -14.5\\,\\text{kJ\/mol}\u0394G\u00b0\u2032=\u2212(2)(96.485)(0.075)\u2248\u221214.5kJ\/mol<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Summary<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Overall \u0394G\u00b0&#8217; for NADH \u2192 O\u2082<\/strong>: <strong>-219.3 kJ\/mol<\/strong><\/li>\n\n\n\n<li><strong>Complex I<\/strong>: \u0394E\u00b0&#8217; = 0.365 V, \u0394G\u00b0&#8217; \u2248 -70.4 kJ\/mol<\/li>\n\n\n\n<li><strong>Complex II<\/strong>: \u0394E\u00b0&#8217; = 0.075 V, \u0394G\u00b0&#8217; \u2248 -14.5 kJ\/mol<\/li>\n\n\n\n<li><strong>Complex III and IV<\/strong>: Follow the same formula using their respective redox couples.<\/li>\n<\/ul>\n\n\n\n<p>These calculations show how electrons flow energetically downhill from NADH to O\u2082, releasing energy used to pump protons and synthesize ATP.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"852\" height=\"1024\" src=\"https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-72.jpeg\" alt=\"\" class=\"wp-image-25628\" srcset=\"https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-72.jpeg 852w, https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-72-250x300.jpeg 250w, https:\/\/gaviki.com\/blog\/wp-content\/uploads\/2025\/06\/learnexams-banner8-72-768x923.jpeg 768w\" sizes=\"auto, (max-width: 852px) 100vw, 852px\" \/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Redox active species along the electron transport chain have reduction potentials between the values of the NAD+\/NADH redox couple (-320 mV) and the oxygen\/water redox couple (+818 mV). Electrons can thereby move down the energy scale toward progressively more positive reduction potentials! Calculate the free energy change \u00ce\u201dG\u00c2\u00ba&#8217; for the final outcome of the NADH [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-25627","post","type-post","status-publish","format-standard","hentry","category-quiz-questions"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/25627","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=25627"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/25627\/revisions"}],"predecessor-version":[{"id":25629,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/25627\/revisions\/25629"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=25627"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=25627"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=25627"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}