Metabolism III: Oxidative Phosphorylation

Electrons

  • For one glucose molecule, glycolysis and the TCA cycle yields:
    • 10 NADH and 10 H+
    • 2 FADH2
  • Each one will carry two high energy electrons
  • Electrons from NADH and FADH2 are used to reduce O2 to H2O
  • Glycerol-3-phosphate and malate-aspartate shuttles allow NADH to cross the inner mitochondrial membrane

Redox potentials

  • In oxidative phosphorylation, the electron transfer potential of NADH+ and FADH2 is converted into the phosphoryl transfer potential of ATP
  • Phosphoryl transfer potential: free energy change during ATP hydrolysis
  • Electron transfer potential: measured by redox potential of a compound (E’0) - how readily it donates electrons
    • Negative (E’0) means the reduced form of compound has a lower affinity for electrons than hydrogen (+ vice versa)

Oxidative phosphorylation

  1. Respiratory chain - electrons handed down from carriers with increasingly positive potentials, transferred onto O2 to form H2O
    1. Oxygen is the final electron acceptor
  1. Transfer of electrons through respiratory chain is coupled to transport of H+ from the mitochondrial matrix
  1. 1, 3 and 4 respiratory complexes pump H+ into the intermembrane space
  1. Flow of H+ back into the matrix through ATP synthases (following concentration gradient) phosphorylates ADP → ATP

Inhibition of oxidative phosphorylation

  • Cyanide, azide and CO inhibits transfer of electrons to O2
  • No proton gradient formed → no ATP synthesized

ATP total

  • From 1 molecule of glucose, through glycolysis, the TCA cycle and oxidative phosphorylation, 30-32 ATP molecules are produced