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OXPHOS

OXPHOS. Electron transport chain Oxidative phosphorylation. The tale thus far…. From one glucose molecule we have ATPs NADHs FADH 2 s 6CO 2. (4). (10). (2). (ATP). Redox reactions. Reduction—gains electrons Oxidation—loses electrons

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OXPHOS

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  1. OXPHOS Electron transport chain Oxidative phosphorylation

  2. The tale thus far…. • From one glucose molecule we have • ATPs • NADHs • FADH2s • 6CO2 (4) (10) (2) (ATP)

  3. Redox reactions • Reduction—gains electrons • Oxidation—loses electrons • In biological systems, protons often accompany the electrons.

  4. Reduction Potentials High Eo' indicates a strong tendency to be reduced Go' = -nFEo' Eo' = Eo'(acceptor) - Eo'(donor) Electrons are donated by the half reaction with the more negative reduction potential and are accepted by the reaction with the more positive reduction potential: Eo’ positive, Go' negative See table 14-2, pg. 429

  5. Example: Half reactions: NAD+  NADH 2 electrons Eº'= -0.32 volts O2  H20 2 electrons Eº'= +0.816 volts Which will be the electron acceptor? Oxygen Eo' = Eo'(acceptor) - Eo'(donor) Eo'= 0.816-(-0.32)= 1.136 V Go' = -nFEo' Go' = -2(23,062 cal/mol-V)(1/136 V) Go' = -52.4 kcal/mole

  6. NADH vs. FADH2 Half reactions: NAD+  NADH 2 electrons Eº'= -0.32 volts FAD  FADH2 2 electrons Eº'= -0.18 volts O2  H20 2 electrons Eº'= +0.816 volts Is more energy or less released in the reoxidation of FAD than NAD+? Less, so fewer ATP's are ultimately made

  7. The tale thus far…. • From one glucose molecule we have • A proton gradient • 6CO2 • 6H2O (ATP)

  8. The Chemiosmotic Theory • Peter Mitchell (1961) • Proton gradient drives ATP synthese • Thus, electron transport is "coupled" to ATP synthesis by the proton gradient

  9. Evidence • Electron transport pumps protons • Complexes are asymmetric in membrane • Membranes with complexes I-IV will do electron transport, but….. • Need an intact membrane for oxphos • Decoupling reagents allow electron transport but not oxphos • Proton gradient is steep enough to drive ATP synthesis (I.e., there's enough energy) • Artificial proton gradients work just fine

  10. How? • F1/Fo ATPase • Makes ATP from ADP and Pi • Can also do the reverse reaction • ATPase activity Early evidence ….

  11. Grand Totals (in theory) • From one glucose molecule we have • 4 ATPs • 10 NADHs  30 ATPs • 2 FADH2s  4 ATPs Total = 38 ATP/glucose But in reality 

  12. Proton gradient used for many things

  13. Cytoplasmic NADH

  14. Reality ~ 30 ATP/glucose

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