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Oxidative Phosphorylation

Biology: AQA A Level, topic 5.2.6

Oxidative Phosphorylation

Oxidative phosphorylation is the final stage in aerobic respiration.

Inner mitochondrial membrane

Inner mitochondrial membrane

  • Oxidative phosphorylation takes place at the inner mitochondrial membrane.
  • There are several features of the membrane that allows production of ATP on a large scale:
  • Three electron carrier proteins (electron transport chain, ETC).
  • ATP synthase enzyme.
  • The space between the inner and outer mitochondrial membranes is called the intermembrane space.
Electron transport chain

Electron transport chain

  • NADH and FADH2 (from the Krebs cycle) are oxidised by the first electron carrier protein in the inner mitochondrial membrane.
  • This initiates oxidative phosphorylation because NADH and FADH2 release two protons and two electrons each.
  • The electrons are then transferred along the ETC.
Proton gradient

Proton gradient

  • As the electrons move down the ETC, they lose energy.
  • This energy pumps the protons from NADH and FADH2 into the intermembrane space.
  • This creates a proton gradient (also known as an electrochemical gradient).
Chemiosmosis

Chemiosmosis

  • The protons diffuse down the concentration gradient through the ATP synthase enzyme.
  • As protons flow through the ATP synthase, energy is released.
  • This energy converts ADP and inorganic phosphate to ATP.
  • This process is called chemiosmosis.
The final electron acceptor

The final electron acceptor

  • After the electrons have reached the end of the ETC and protons have flowed through the ATP synthase enzyme, they combine with O2 to form water (H2O).
  • Oxygen is called the final electron acceptor for this reason.

Test yourself on Oxidative Phosphorylation

  • Stages in Oxidative Phosphorylation

  • Which molecule is the final electron acceptor?

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