CIE A Level Biology (9700) 2019-2021

Revision Notes

12.2.6 Aerobic Respiration: Oxidative Phosphorylation

Oxidative Phosphorylation

  • Oxidative phosphorylation is the last stage of aerobic respiration
  • It takes place at the inner membrane of the mitochondria
  • Several steps occur:
  • Hydrogen atoms are donated by reduced NAD and FAD
  • Hydrogen atoms split into protons and electrons
  • The high energy electrons release energy as they move through the electron transport chain
  • The released energy is used to transport protons across the inner mitochondrial membrane from the intermembrane space into the matrix
  • A concentration gradient of protons is established between the intermembrane space and the matrix
  • The protons return to the matrix via facilitated diffusion through the channel protein ATP synthase
  • The movement of protons down their concentration gradient provides energy for ATP synthesis
  • Oxygen combines with protons and electrons at the end of the electron transport chain to form water

The electron transport chain

  • The electron transport chain is made up of a series of membrane proteins/ electron carriers
  • They are positioned close together which allows the electrons to pass from carrier to carrier
  • The inner membrane of the mitochondria is impermeable to hydrogen ions so these electron carriers are required to pump the protons across the membrane to establish the concentration gradient

Exam Tip

Examiners often ask why oxygen is so important for aerobic respiration. Oxygen acts as the final electron acceptor. Without oxygen the electron transport chain cannot continue as the electrons have nowhere to go. Without oxygen accepting the electrons (and hydrogens) the reduced coenzymes NADH and FADH2 cannot be oxidised to regenerate NAD and FAD, so they can’t be used in further hydrogen transport.

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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