electron transport chain

A sequence of biochemical reduction-oxidation reactions that effects the transfer of electrons through a series of carriers. An electron transport chain, also known as the respiratory chain, forms the final stage of aerobic respiration. It results in the transfer of electrons or hydrogen atoms derived from the Krebs cycle to molecular oxygen, with the formation of water. At the same time it conserves energy from food or light in the form of ATP. The chain comprises a series of carrier molecules that undergo reversible reduction-oxidation reactions, accepting electrons and then donating them to the next carrier in the chain – a process known as electron flow. In the mitochondria, NADH and FADH₂, generated by the Krebs cycle, transfer their electrons to a chain including coenzyme Q (see ubiquinone) and a series of cytochromes. This process is coupled to the formation of ATP at three sites along the chain. The ATP is then carried across the mitochondrial membrane in exchange for ADP. An electron transport chain also occurs in photosynthesis.

Electron transport chain