Oxidative Phosphorylation (AQA A Level Biology): Revision Note

Exam code: 7402

Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Naomi Holyoak

Updated on

Aerobic respiration: oxidative phosphorylation

  • Oxidative phosphorylation is the final stage of aerobic respiration

    • It takes place on the cristae of the inner mitochondrial membrane

    • It relies on proteins embedded in the membrane, e.g. ATP synthase enzymes

    • The large surface area of the folded cristae provides many locations for oxidative phosphorylation to occur

Diagram of a mitochondrion showing labelled parts: matrix, ribosome, mitochondrial DNA, cristae, membranes, intermembrane space, and ATP synthase.
Oxidative phosphorylation involves ATP synthase enzymes on the cristae of the mitochondria
  • During oxidative phosphorylation:

    1. hydrogen atoms are donated by reduced NAD and reduced FAD from the Krebs cycle

    2. hydrogen atoms split into protons (H+ ions) and electrons

    3. the electrons enter the electron transport chain; energy is released as they pass between electron carriers

      • The electron transport chain is made up of electron carrier proteins that are embedded in the inner mitochondrial membrane

    4. the released energy is used to actively transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space

    5. the protons move down their concentration gradient back to the matrix by facilitated diffusion; they move via proton channels that are associated with ATP synthase

      • This movement of protons is known as chemiosmosis

    6. ATP synthase catalyses the formation of ATP from ADP and Pi

  • At the end of the electron transport chain the electrons pass to oxygen, which acts as the final electron acceptor

    • Oxygen combine with protons and electrons at the end of the electron transport chain to form water as a waste product

Diagram illustrating the electron transport chain in mitochondria, with proteins pumping protons, forming a gradient, and ATP synthesis via ATP synthase.
Oxidative phosphorylation by chemiosmosis occurs on the inner mitochondrial membrane and requires NADH and FADH2 from the Krebs cycle; it produces water and many molecules of ATP

Examiner Tips and Tricks

Remember that oxidative phosphorylation produces ATP; you should never say that energy is produced.

Make sure that you understand the role of oxygen in oxidative phosphorylation; it acts as a final electron acceptor, allowing the electron transport chain to continue functioning normally.

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Alistair Marjot

Author: Alistair Marjot

Expertise: Environmental Systems and Societies & Biology Content Creator

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

Naomi Holyoak

Reviewer: Naomi Holyoak

Expertise: Biology Content Creator

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.

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