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Chapter 20 · Electron Transport and Oxidative PhosphorylationChapter 20Electron Transport andOxidative Phosphorylation. . . . . . . . . . . . . . . . . . . . . . . .Chapter OutlineOxidative phosphorylation driven by electron transportMembrane associated processesPlasma membrane of bacteriaMitochondrial membrane of eukaryotesOuter mitochondrial membrane: Permeable to Mr < 10,000 due to protein porinIntermembrane space: Creatine kinase, adenylate kinase, cytochrome cInner mitochondrial membrane: Highly impermeableoHigh protein contentoHigh content of unsaturated fatty acidsoCardiolipin and diphosphatidylglycerol: No cholesteroloCristae: Folds that increase surface areaMatrixoTCA cycle enzymes (except succinate dehydrogenase)oEnzymes for catabolism of fatty acidsoCircular DNAoRibosomes, tRNAsReduction potentials: Electrical potential generated when reactions involve movement of electronsStandard reduction potentials: Eo’Measured using sample half-cell with oxidized and reduced forms at 1MReference half-cell 1M H+ and H2 gas at 1 atmElectrons flow toward cell with larger positive reduction potentialHalf-cell reactions written as reduction reaction: Electrons on reactant sidePositive values of Eo’: Accept electrons: Oxidizing agentsNegative values of Eo’: Donate electrons: Reducing agents Standard free energy change related to standard reduction potential∆G°’ = -nF∆Eo’n = number of electronsF = Faraday’s constant: 96,485 J/V∙mol∆Eo’ = Eo’(final)-Eo’(initial)Electron transport chainElectron mediatorsFlavoproteins: Tightly bound FMN or FADCoenzyme Q (ubiquinone): 1 or 2 Electron transfers: Mobile within membrane53
Chapter 20 · Electron Transport and Oxidative PhosphorylationCytochromes: Fe2+/Fe3+Cytochrome a’s: Isoprenoid (15-C) on modified vinyl and formyl in place of methylCytochrome b’s: Iron-protoporphyrin IXCytochrome c’s: Iron-protoporphyrin IX linked to cysteineIron-sulfur proteins: Fe2+/Fe3+: Several typesProtein-bound copper: Cu+/Cu2+Electron transport complexes: FourComplex I: NADH-coenzyme Q reductase (NADH reductase)Electron movemento[FMN] accepts electron pair from NADHo[FMNH2] donates electrons to Fe-SoFe-S donates electrons to coenzyme QProtons pumped from matrix to cytosolSupports 3 ATPComplex II: Succinate-coenzyme Q reductase (succinate dehydrogenase)ComponentsoFADoFe-S centersNo protons pumpedSupports 2 ATPSimilar complexesoGlycerolphosphate dehydrogenase: Reduces coenzyme Q: No protons pumpedoFatty acyl-CoA dehydrogenase: Reduces coenzyme Q: No protons pumpedComplex III: Coenzyme Q-cytochrome c reductaseComponentsoCytochromes bL and bHoRieske protein: Fe-S proteinQ-cycleProtons pumpedComplex IV: Cytochrome c oxidaseComponentsoCytochrome a and CuAoCytochrome a3 and CuBBinuclear center: O2 consumption and H2O productionProtons pumped