The chain pumps protons out. ATP synthase lets them in
- The idea
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- Why
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The idea
“ATP synthase pumps protons out of the matrix, and that's how it makes ATP.”
The electron transport chain and ATP synthase sit in the same membrane, and both move H+. It's easy to swap which one pushes H+ out.
The short version
The mistake: ATP synthase pumps protons out of the matrix, and that's how it makes ATP.
What's actually true: The electron transport chain pumps H+ out of the matrix. H+ flows back in through ATP synthase, down its gradient, making ATP.
- Pumping builds a proton gradient, with more H+ in the intermembrane space than in the matrix. It's stored energy, like water behind a dam.
- As H+ flows down that gradient through ATP synthase, it turns part of the enzyme. That motion joins ADP and phosphate into ATP. This is chemiosmosis.
- ATP synthase can run in reverse, spending ATP to push H+ out. When it makes ATP, H+ is always flowing in.
On the exam: The chain pumps H+ out. ATP synthase lets it back in, and that flow makes ATP.