Respiration

The electron transfer chain is the final series of biochemical reactions in cellular respiration. It consists of a series of organic electron carriers associated with the inner membrane of the mitochondria. Cytochromes are among the most important of these electron carriers. Like hemoglobin, cytochromes are colored proteins which contain iron in a nitrogen-containing heme group. The final electron acceptor of the electron transfer chain is oxygen, which produces water as a final product of cellular respiration (see equation 1).

The main function of the electron transfer chain is the synthesis of 32 molecules of ATP from the controlled oxidation of the eight molecules of NADH and two molecules of FADH₂, made by the oxidation of one molecule of glucose in glycolysis and the citric acid cycle. This oxygen-requiring process is known as oxidative phosphorylation.

The electron transfer chain slowly extracts the energy from NADH and FADH₂ by passing electrons from these high energy molecules from one electron carrier to another, as if along a chain. As this occurs, protons (H⁺) are pumped across the inner membrane of mitochondria, creating a proton gradient which is subsequently used to make ATP by a process known as chemiosmosis.