7.4—Oxidative phosphorylation

Reduced NAD and FAD donate electrons to the inner-membrane electron transport chain. Energy released pumps protons into the intermembrane space; their return through ATP synthase drives ADP phosphorylation.

Oxygen is the final electron acceptor, combining with electrons and protons to form water. Without oxygen, carriers remain reduced, proton pumping stops and oxidative ATP production collapses.

A proton gradient is like stored potential energy: blocking ATP synthase prevents its controlled use, while making the inner membrane leaky dissipates the gradient as heat.

Chemiosmosis is not direct phosphorylation by oxygen, and the exact ATP yield depends on the accounting convention. Keep proton gradient, ATP synthase and final acceptor separate.