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Exploring Oxidative Phosphorylation: The Journey from Glucose to ATP

This overview of the oxidative phosphorylation process delves into the electron transport chain's functioning, providing insights into the energy yield from a single glucose molecule. It examines the roles of NADH and FADH2 in ATP production, the significance of reduction potentials, and the importance of the proton gradient in ATP synthesis. We discuss the chemiosmotic theory proposed by Peter Mitchell and how proton gradients drive ATP synthesis in biological systems. The theoretical vs. practical ATP yield is also compared, revealing a realistic output of approximately 30 ATPs per glucose.

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Exploring Oxidative Phosphorylation: The Journey from Glucose to ATP

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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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