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Lecture 12 Oxidative Phosphorylation

Lecture 12 Oxidative Phosphorylation - Electron Transport...

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Electron Transport and Oxidative Phosphorylation Stryer Chapter 18 Mitochondria Electron transfer Proton pumps/Proton gradient Movement across membranes Regulation 1
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The TCA cycle, electron transport, and oxidative phosphorylation occur in the mitochondria - the energy generators of the cell Outer membrane is permeable to small molecules Inner membrane is not - ATP, pyruvate, and citrate are transported specifically ~ 2 µm x 0.5 µm 2
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Overview of Oxidative Phosphorylation 3
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NADH and FADH 2 pass their electrons to O 2 to produce H 2 O and by doing so, create a proton gradient used for Oxidative-Phosphorylation I II III IV 4
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Redox Potentials are related to Gº’ Gº’ = -RT ln K eq pH = 7 Gº’ = -n F E 0 ’ = -RT ln K eq pH = 7 Gº’ = -n(23 kcal/mol/V) E 0 X red + H + ==> X ox + 1/2 H 2 X red ==> X ox + e H + + e ==> 1/2 H 2 E 0 ’ = Standard reduction potential at pH 7.0 and 25 °C (oxidant + e - reductant) E 0 ’ = Change in the standard reduction potential F = Faraday constant = 23.06 kcal mol -1 V -1 n = number of electrons 5
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A Theoretical Electrochemical Cell for Measuring Standard Redox Potentials Allows ions to cross for electrical flow 6
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Calculating Gº’ for a reaction Pyruvate + NADH + H + <==> Lactate + NAD + Pyruvate + 2 H + + 2 e ==> Lactate E 0 ’ = – 0.19 V NAD + + H + + 2 e ==> NADH E 0 ’ = – 0.32 V NADH ==> NAD + = H + + 2 e E 0 ’ = + 0.32 V Therefore: Pyruvate + NADH + H + <==> Lactate + NAD + E 0 ’ = + 0.13 V Gº’ = – n F E 0 pH = 7 Gº’ = – n(23 kcal/mol/V) E 0 = – 2(23 kcal/mol/V)(0.13V) = – 6 kcal/mol 8
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Energy-rich NADH passes electrons down an energy gradient into complexes with energy differences useful for synthesizing ATP I II III IV 9
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Flavin mononucleotide (FMN) FMN functions similarly to FAD; both can be in oxidized, reduced, or semiquinone (1 e ) states 10
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Coenzyme Q is an important electron carrier in the mitochondrial membrane Coenzyme Q can also exist in 3 redox states: Oxidized (ubiquinone), a partially reduced semiquinone intermediate, and fully reduced (ubiquinol). The isoprene tail (blue) embeds this coenzyme in the mitochondrial membrane where it functions. 11
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[2Fe-2S] [4Fe-4S] Iron Sulfur [Fe-S] centers transmit electrons and (usually) have low redox potentials Fe S Fe S N S S N N N Rieske [2Fe-2S] 12
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Hemes like in hemoglobin: It uses Fe(II) and Fe(III) states for electron transfer Fe can change between Fe(II) and Fe(III) redox states.
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