chemiosmotic theory A theory postulated by the British biochemist Peter Mitchell (1920–92) to explain the formation of ATP in the mitochondrial electron transport chain. As electrons are transferred along the electron carrier system in the inner mitochondrial membrane, hydrogen ions (protons) are actively transported (by proton pumps) into the space between the inner and outer mitochondrial membranes, which thus contains a higher concentration of protons than the matrix. This creates an electrochemical gradient across the inner membrane, down which protons move back into the matrix. This movement occurs through special channels associated with ATP synthetase, the enzyme that catalyses the conversion of ADP to ATP, and is coupled with the phosphorylation of ADP (see illustration). A similar gradient is created across the thylakoid membranes of chloroplasts during the light-dependent reactions of photosynthesis (see photophosphorylation).

chemiosmotic theory A theory concerning oxidative phosphorylation in which it is proposed that the electron-transport chain is arranged such that it generates an energy-rich proton gradient across the inner membrane of a mitochondrion, and electrons cross the membrane by a mechanism reminiscent of that in which molecules of solvent cross a semi-permeable membrane in osmosis. The energy is then used to drive the phosphorylation of ADP through a membrane-bound ATP-ase.

chemiosmotic theory A theory concerning oxidative phosphorylation in which it is proposed that the electron-transport chain is arranged such that it generates an energy-rich proton gradient across the inner membrane of a mitochondrion. This energy is then used to drive the phosphorylation of ADP through a membrane-bound ATP-ase.