CHAPTER 10A

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Chapter 10:

From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Chapter 10 Section 10.1: Electron Transport Section 10.2: Oxidative Phosphorylation Section 10.3: Oxygen, Cell Function, and Oxidative Stress Biochemistry in Perspective Aerobic Metabolism II: Electron Transport and Oxidative Phosphorylation Overview

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Electron transport chain is a series of electron carriers in order of increasing electron affinity Aerobic respiration couples electron transfer ultimately to ATP synthesis Figure 10.1 The Electron Transport Chain

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Electron Transport and Its Components Located in the inner mitochondrial membrane Most components of the electron transport chain (ETC) are located in four complexes Figure 10.1 The Electron Transport Chain

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Complex I (NADH dehydrogenase complex) catalyzes transfer of electrons from NADH to ubiquinone (UQ) 25 different polypeptides One molecule of flavin mononucleotide and seven iron-sulfur centers Figure 10.2 Two Iron-Sulfur Centers

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Electrons transferred from NADH to FMN, yielding FMNH 2 Then from FMNH 2 to iron sulfur centers Eventually electrons transferred to ubiquinone Figure 10.3 Structure and Oxidation States of Coenzyme Q (UQ)

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Electron movement accompanied by a net movement of protons from the matrix to the intermembrane space UQ is lipid-soluble and shuttles electrons between ETC complexes along the inner mitochondrial membrane Figure 10.4 Electron Movement Through Complex I of the Electron Transport Chain

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Complex II (succinate dehydrogenase complex) transfers electrons from succinate to UQ It contains succinate dehydrogenase and two iron-sulfur proteins Figure 10.5 Path of Electrons from Succinate, Glycerol-3-Phosphate, and Fatty Acids to UQ

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press The larger iron-sulfur protein has succinate oxidation site and is covalently bound to FAD UQ can also get electrons from acyl-CoA and glycerol-3-phosphate dehydrogenases Figure 10.5 Path of Electrons from Succinate, Glycerol-3-Phosphate, and Fatty Acids to UQ

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Complex III (cytochrome b 1 complex) transfers electrons from reduced UQ (UQH 2 ) to cytochrome c (cyt c) Cytochromes are proteins with a heme prosthetic group Electrons change oxidation state of heme iron (reduced Fe 2+ and oxidized Fe 3+ ) Figure 10.6 Structure of Cytochrome C

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Cytochrome c is a water soluble mobile electron carrier of the outer face of the inner membrane Q cycle is the transfer of electrons through complex III For each pair of electrons that are transported through complex III, two molecules of cyt c are reduced Figure 10.7 Electron Transport Through Complex III

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Complex IV (cytochrome oxidase) catalyzes the four electron reduction of O 2 to H 2 O Contains cytochrome a, a 3 , and three copper ions Figure 10.8 Electron Transport Through Complex IV

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Cu A -Cu A accepts electrons, passes them to cytochrome a, and then a 3 -Cu B Finally four electrons and protons are passed to O 2 to form H 2 O Figure 10.8 Electron Transport Through Complex IV

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press ATP can act as an allosteric inhibitor of cytochrome oxidase by binding to complex IV Figure 10.8 Electron Transport Through Complex IV

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press NADH oxidation results in a substantial energy release The energy is used to pump protons into the intermembrane space, establishing a proton gradient to generate ATP 2.5 molecules of ATP synthesized per NADH 1.5 molecules of ATP synthesized per FADH 2 Figure 10.9 Energy Relationships in the Electron Transport Chain

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press

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Section 10.1: Electron Transport From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Electron Transport Inhibitors Several molecules specifically inhibit the electron transport process When electron transport is inhibited, O 2 consumption is reduced or eliminated Important for understanding the correct order of ETC components Figure 10.10 Inhibitors of the Electron Transport Chain

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Section 10.2: Oxidative Phosphorylation From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Oxidative phosphorylation is the process that conserves the energy of the ETC by phosphorylation of ADP to ATP The chemiosmotic coupling theory explains how oxidative phosphorylation links the ETC and ATP synthesis Figure 10.11 Overview of the Chemiosmotic Model

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press The Chemiosmotic Theory 1. As electrons pass through ETC, protons are pumped into the intermembrane space generating proton motive force 2. Protons move back across the membrane through ATP synthase driving ATP formation Figure 10.11 Overview of the Chemiosmotic Model Section 10.2: Oxidative Phosphorylation

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Evidence for the chemiosmotic theory : 1. pH drops in a weakly buffered mitochondria suspension when actively respiring 2. Disruption of inner membrane stops respiration 3. Uncouplers and ionophores (e.g., Gramicidin A) disrupt the proton gradient, inhibiting ATP synthesis Figure 10.12 Uncouplers Section 10.2: Oxidative Phosphorylation

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ATP Synthesis ATP synthesis requires translocation of three protons through the ATP synthase ATP synthase consists of two rotors linked by a strong flexible stator Two major components: F 1 unit (ATP synthase ) and F 0 unit (transmembrane channel) From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 10.13 The ATP Synthase Section 10.2: Oxidative Phosphorylation

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