Electron flow and ATP synthesis are separate steps
- The idea
- Predict
- See it
- Why
- Check
The idea
“When electrons move down the chain, that movement itself makes the ATP.”
Electrons release energy and ATP gets made, so it's easy to picture that energy going straight into ATP. It pumps H+ first.
The short version
The mistake: When electrons move down the chain, that movement itself makes the ATP.
What's actually true: The chain uses electron flow to pump H+, and ATP synthase makes ATP from H+ flowing back. The H+ gradient is their only link.
- As electrons pass along the electron transport chain, it pumps H+ across the membrane, building a gradient. Chloroplasts do the same.
- H+ flowing back through ATP synthase spins part of the enzyme, which joins ADP and phosphate. This is chemiosmosis.
- Collapse the gradient and electrons still flow, but the synthase stops. Build one another way, like the acid bath, and ATP is made without electron flow.
On the exam: Electron flow builds the H+ gradient. The gradient runs ATP synthase. Break it and the two come apart.