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Lecture 21

Lecture 21. Mitochondrial Electron Transfer. Biological Electron Flow Does Work. Mitochondrial Electron Carriers. NADH and FADH 2 (Flavoproteins) Dehydrogenases Iron-sulfur proteins Cytochromes Cu Ubiquinone (Coenzyme Q CoQ). Highly organized complexes on inner mitochondrial membrane.

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Lecture 21

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  1. Lecture 21 Mitochondrial Electron Transfer

  2. Biological Electron Flow Does Work

  3. Mitochondrial Electron Carriers • NADH and FADH2 (Flavoproteins) • Dehydrogenases • Iron-sulfur proteins • Cytochromes • Cu • Ubiquinone (Coenzyme QCoQ) Highly organized complexes on inner mitochondrial membrane

  4. Nicotinamide-Adenine Dinucleotide

  5. Reduction of Flavin Nucleotides

  6. Iron-Sulfur Proteins (Fe-S) Fe+3 + e– Fe2+ Fe-S clusters: Fe between +3 and +2 oxidation states Redox range [2Fe-2S]2+/1+:-240 to -460 mV [4Fe-4S]3+/2+:50 to 450mV

  7. Heme in cytochrome

  8. Electron-Transfer Complexes: H+ Pumps As electrons flow to O2, H+ flows out

  9. Electron transfer complexes • I: NADH Q oxidoreductase • II: Succinate dehydrogenase • III: Ubiquinone cytochrome c • oxidoreductase • IV: Cytochrome oxidase In between some complexes:electron carriers that diffuse out of complex

  10. Carrier Order by Inhibition • Carriers ahead of block are reduced • Carriers behind block are oxidized

  11. Complex I:NADH Ubiquinone oxidoreductase NADH + H+ +Q NAD+ + QH2

  12. Electron-Transfer Complexes: H+ Pumps As electrons flow to O2, H+ flows out

  13. Ubiquinone  UQ  CoQ Two electron carrier

  14. Q cycle:Complex III

  15. Complex IV Redox centers: Carry only 1e- at a time. Reactive intermediates are generated.

  16. Order of Carriers: Ascending Eo

  17. Respiration in Mitochondria • 3 reactions • Substrate is oxidized • O2 consumed (H2O) • ADP + Pi  ATP

  18. Uncoupling Agents and Conditions • Allow electron flow without ATP synthesis • Example: 2,4-dinitrophenol (DNP) • Others: CCCP, ionophores, membrane disruption

  19. + 1 + NADH + H + / O H O + NAD 2 2 2 o ∆G ' = –220 kJ/mol ADP + P ATP i o ∆G ' = +30.5 kJ/mol Efficiency of Oxidative Phosphorylation

  20. Observed P/O Ratios

  21. Phosphorylation “Substrate-level” vs. “Respiration-linked”

  22. Chemiosmotic Energetics In mitochondria ∆GH+=15-25 kJ/mol H+

  23. Predictions of Chemiosmotics 1. Electron transfer causes H+ flux 2. Destruction of H+ gradient blocks ATP synthesis 3. Artificially-induced H+ gradient drives ATP synthesis without electron transfer 4.Blocking ATP synthesis will eventually inhibit electron transfer

  24. H+ Flux Across Mitochondrial Membrane

  25. Uncouplers: Permeant H+ Carriers Destroys H+ gradient

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