The remarkable properties that allow ATP synthase to run in either direction allow the interconversion of energy stored in the H⁺ gradient and energy stored in ATP to proceed in either direction.

(A) If ATP synthase making ATP can be likened to a water-driven turbine producing electricity, what would be an appropriate analogy when it works in the opposite direction?

(B) Under what conditions would one expect the ATP synthase to stall, running neither forward nor backward?

(C) What determines the direction in which the ATP synthase operates?