12.2.4

Chemiosmosis & Coenzymes

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Chemiosmotic Theory

Chemiosmotic theory explains how oxidative phosphorylation and photophosphorylation work in relation to the production of ATP.

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Chemiosmosis

  • Chemiosmosis is the movement of ions across a membrane down an electrochemical gradient.
  • ATP synthesis is an example of chemiosmosis because protons move across a membrane down an electrochemical gradient.
  • Chemiosmosis happens in photophosphorylation and oxidative phosphorylation.
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ATP synthase

  • ATP synthase is an enzyme found in the inner mitochondrial membrane of mitochondria, and in the thylakoid membrane of chloroplasts.
  • Protons flow through ATP synthase, which releases energy needed to make ATP from ADP and P.
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Proton gradients

  • In mitochondria, protons are pumped from the matrix into the intermembrane space and in chloroplasts, protons are pumped from the stroma into the thylakoids.
  • The energy needed to pump protons across the membrane comes from the electron transport chain.
  • Pumping protons creates an electrochemical gradient. Protons move down the electrochemical gradient through ATP synthase, releasing energy.
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Electron transport chain (ETC)

  • The electron transport chain (ETC) is a series of electron carrier proteins in the thylakoid membrane and the inner mitochondrial membrane.
  • As electrons move down the ETC, they lose energy, which is used to pump protons across the membrane.
  • In respiration, electrons come from the oxidation of NADH and FADH2.
  • In photosynthesis, electrons come from the photoionisation of chlorophyll.

Coenzymes in Respiration

NAD, FAD, and Coenzyme A are important coenzymes in respiration:

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NAD

  • NAD is a coenzyme that can be reduced to NADH.
  • NADH is produced in glycolysis (2 molecules per glucose), the link reaction (1 molecule per pyruvate), and the Krebs cycle (3 molecules per acetate).
  • NADH gets oxidised in oxidative phosphorylation, releasing electrons for the ETC and protons.
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FAD

  • FAD is a coenzyme that can be reduced to FADH2.
  • FADH2 is produced in the Krebs cycle (1 molecule per acetate).
  • FADH2 gets oxidised in oxidative phosphorylation, releasing electrons for the ETC and protons.
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Coenzyme A

  • Coenzyme A binds with acetate in the link reaction to form acetyl coenzyme A, which goes on to enter the Krebs cycle.
  • The link reaction links together glycolysis and the Krebs cycle.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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