What role does the mitochondrial membrane potential play in ATP production?

• A. It stores energy in the form of GTP.
• B. It pumps water across the membrane.
• C. The membrane potential powers ATP synthase by driving protons back into the matrix.
• D. It directly phosphorylates ADP to ATP without enzymes.

Answer: (C)

The energy that drives ATP production in mitochondria comes from the proton motive force, a combination of a membrane potential and a proton gradient created by the electron transport chain. The membrane potential is the electrical part of that force: protons are pumped from the matrix into the intermembrane space, making the outside positively charged relative to the inside. This electrical gradient, along with the pH gradient, creates a strong drive for protons to flow back into the matrix through the F0 portion of ATP synthase.

As protons move through ATP synthase, the flow of protons causes the enzyme to rotate and convert ADP and inorganic phosphate into ATP. In other words, the membrane potential provides the energy that powers ATP synthase to drive ATP formation. If the potential dissipates, the proton flow slows and ATP production decreases or stops.

This mechanism is not about storing energy as GTP, nor about pumping water, nor does ATP synthase directly phosphorylate ADP without enzymes. The membrane potential specifically powers ATP synthase by guiding protons back into the matrix to synthesize ATP.