Chemiosmosis: Higher Level only: This statement is Higher Level only. It completes the story of 3.2.14: the gradient is spent making ATP.
Practise this as you read
- Explain how chemiosmosis produces ATP.
- State the location of ATP synthase.
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The big idea: The protons pumped into the intermembrane space can only get back into the matrix through ATP synthase. As they diffuse down their gradient through it, the enzyme uses the energy released to phosphorylate ADP, making ATP. This is chemiosmosis.
The points to remember
- A high proton concentration builds in the intermembrane space.
- The inner membrane is impermeable to protons, except through ATP synthase.
- Protons diffuse back into the matrix through ATP synthase (facilitated diffusion).
- The energy released drives ADP + phosphate → ATP.
- ATP synthase is in the inner membrane, on the cristae.
Remember it as: Chemiosmosis: protons rush back through the turnstile, and each turn makes ATP.
Real example: antibiotics that block ATP synthase. Some newer antibiotics against tuberculosis work by blocking the bacteria's ATP synthase, so the cells cannot make ATP by chemiosmosis.
Trap: Protons diffuse through ATP synthase (down the gradient); they are pumped only by the electron transport chain.
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How it is asked: Expect a short question on where ATP synthase is, and an Explain on how chemiosmosis produces ATP.
IB-style questionExplain[4 marks]
Explain how ATP is produced by chemiosmosis in mitochondria.
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