Explain the process of oxidative phosphorylation and the electron transport chain in the production of ATP in respiration.

Oxidative phosphorylation and the electron transport chain (ETC) are both aerobic processes that require oxygen. These processes occur in the mitochondria of cells across the inner mitochondrial membrane. Electrons are released from reduced coenzymes NADH and FADH (produced in glycolysis and the citric acid cycle) in the matrix and are passed along electron carrier proteins embedded in the inner mitochondrial membrane down the energy gradient releasing energy. This energy is used to actively pump H+ ions (protons) from the matrix into the inter membrane space. Protons then flow passively down their electrochemical gradient back into the matrix through the ATP synthase enzyme protein channel; this proton motive force catalyses the reaction between ADP and Pi to form ATP. Electrons at the end of the ETC and protons (H+) combine with oxygen (the final electron acceptor) to form water - a by-product of respiration.