The oxidative phosphorylation cycle is the process by which cells within the human body produce adenosine triphosphate, ATP, via the electron transport chain, an aerobic energy system that follows the Krebs cycle in the body’s never-ending production of energy. Oxidative phosphorylation takes place within the matrix and inter-membrane space of the mitochondria within each cell. NADH and FADH2, generated by the Krebs cycle, donate their protons and electrons to the electron transport chain, which ultimately produces ATP and H2O.
The electrons from the NADH and FADH2 are donated to Complexes I through IV, while the protons are shuttled back into the matrix of the mitochondria. In complex IV, the electrons are combined with O2 and H+ molecules to form water, or H2O, while Complexes I, III, and IV move the protons into the inter-membrane space where they are diffused back into the mitochondrial matrix via Complex V, or FoF1 ATP synthase, resulting in the production of ATP molecules.
There are 5 complexes involved in the oxidative phosphorylation cycle: Complex I, or NADH dehydrogenase, Complex II, succinate-ubiquinone oxidoreductase, Complex III, Ubiquinol-cytochrome c oxidoreductase also called Coenzyme Q, Complex IV, cytochrome c oxidase, and Complex V, FoF1 ATP synthase.
Medeiros, D.M. & Wildman, R.E.C.. (2012). Advanced Human Nutrition. Jones & Bartlett Publishers. ISBN: 9780763780395.