Electron transfer chain

The electron transfer chain, also called the electron transport chain, is a sequence of complexes found in the mitochondrial membrane that accept electrons from electron donors such as NADH or succinate, shuttle these electrons across the mitochondrial membrane creating an electrical and chemical gradient, and through the proton driven chemistry of the ATP synthase (aka the F₀F₁ particle), generate adenosine triphosphate.

There are five complexes normally associated with the electron transfer chain.

Complex I - NADH dehydrogenase, also called NADH Coenzyme Q reductase.
Complex II - Succinate - Coenzyme Q reductase.
Complex III - Coenzyme Q - cytochrome c reductase.
Complex IV - Cytochrome c oxidase.
Complex V - ATP Synthase, also known as the F₀F₁ particle.

All of these are proteolipid complexes, with the first four containing either flavins, iron-sulfur clusters, copper centers, or heme moieties. Complexes I, III, and IV are proton pumps. Complex II is part of the Krebs cycle and does not pump protons, and Complex V uses the electrochemical potential generated to create ATP. Complex IV is the terminus of the electron transfer chain, consuming oxygen and making water.

Cytochrome c

Cytochrome c is also an essential part of the electron transfer chain. It is a soluble protein loosely associated with the inner mitochondrial membrane, and transfers electrons between Complexes III and IV.