oxidative phosphorylation

The formation of ATP from ADP and inorganic phosphate coupled to the movement of electrons down the *respiratory chain. ATP formation occurs at three sites on the respiratory chain: during the transfer of electrons from NAD to coenzyme Q; during the transfer of electrons from cytochrome b to cytochrome c; and during the transfer of electrons from cytochrome aa₃ to oxygen. The nature of the link between oxidative phosphorylation and the respiratory chain is not understood although there are several theories to explain it. The most widely supported theory suggests that the respiratory chain creates a pH gradient across the internal mitochondrial membrane and that the potential energy of this gradient is then utilized to convert ADP to ATP.