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 RESPIRATION

THE ELECTRON TRANSPORT CHAIN (ETC)

  • Most ATP is manufactured by oxidative phosphorylation.
  • A series of redox reactions using electron acceptor/donor molecules coupled to glycolysis and the Kreb's cycle.
  • The electron acceptors/donors reduce (when receiving electrons) and oxidise (when losing electrons) one another along an electrochemical gradient. Each molecule in the series has a lower redox potential than the one before.
  • Each redox reaction results in a release of energy.
  • If this energy release is > 30.5 kJ mol-1 a mole of ATP can be synthesised from ADP by a coupled reaction.
  • The first molecule in the series is NAD (or FAD), a coenzyme of various dehydrogenase enzymes.

    NAD (oxidised) NADH + H+ (reduced)
  • Next come a series of iron containing proteins called cytochromes
  • The last electron acceptor in the series is oxygen.
  • Electrons are produced by splitting hydrogen atoms taken from the food molecules (H H+ + e-) by dehydrogenases. Thus at the end of the ETC:

2H+ + 2e- + ½O2 H2O

The location of the ETC

The mitochondrial inner membrane of eukaryotes (the plasma membrane of prokaryotes).

Surface area increased by cristae. Density of cristae is proportional to activity of the cell. For example:

 Liver cell 40 m2 g-1 mitochondria
Heart muscle 200 to 250 m2 g-1 mitochondria

The Mechanism: THE CHEMIOSMOTIC PUMP

The ETC creates a concentration gradient by pumping H+ out of the mitochondrial inner matrix. As these H+ diffuse back into the matrix across the inner membrane they drive ATP synthesis.

© Paul Billiet 2008