[ELI5] What causes the Fo structure of ATP synthase to rotate?

Question

[ELI5] What causes the Fo structure of ATP synthase to rotate?

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Answer 1

This very much is not an ELI5 question, as its answer is complicated, but it’s about the motion of protons from the inner mitochondrial membrane back into the inner mitochondria. This movement of protons, powered by the concentration gradient generated by the electron transport chain, causes the F0 subunit to rotate. It takes 4 protons moving through the F0 to make one ATP molecule (one proton per each of the three conformational changes required to for the ADP to ATP reaction, and a fourth the release the ATP).

Edit: also, because there are three catalytic oligomers in the F0, each full rotation requires 12 protons and generates 3 ATP molecules