Oxidative phosphorylation occurs when the reducing powers NADH and FADH2 are oxidized via an electron transport chain. During their oxidation, the protons are pumped across the inner mitochondrial membrane to generate the proton concentration gradient. This gradient drives the facilitated diffusion of protons through proton channels of the ATP synthase and phosphorylation of ADP into ATP. This process of ADP phosphorylation is called oxidative phosphorylation since the energy of the proton concentration gradient generated during oxidation of reducing powers drives the process.
