Here's how it works:
1. Electron transport chain: Electrons from the breakdown of glucose are passed along a chain of protein complexes embedded in the inner mitochondrial membrane.
2. Proton pumping: As electrons move down the chain, energy is released and used to pump protons (H+) from the mitochondrial matrix across the inner membrane into the intermembrane space.
3. Proton gradient: This pumping creates a concentration gradient of protons, with a higher concentration in the intermembrane space than in the matrix. This gradient represents a stored form of potential energy.
4. ATP synthase: The proton motive force drives protons back across the membrane through ATP synthase, a protein complex that acts like a tiny turbine.
5. ATP synthesis: The flow of protons through ATP synthase provides the energy needed to convert ADP and inorganic phosphate (Pi) into ATP.
Therefore, the PMF, consisting of both the chemical potential (proton concentration gradient) and the electrical potential (charge difference across the membrane), is the direct energy source that powers ATP synthesis during oxidative phosphorylation.
