Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients thereby releasing energy in order to produce adenosine triphosphates (ATP) in eukaryotes; this takes place inside the mitochondria. Almost call aerobic organisms carry out oxidative phosphorylation. The energy stored in the chemical bonds of glucose is released by the cell in the citric acid cycle producing carbon dioxide, and the energetic electro donors NADH and FADH. Oxidative phosphorylation uses these molecules and oxygen (O₂) to produce ATP which is used throughout the cell whenever energy is needed. During oxidative phosphorylation, electrons are transferred from the electron donors to a series of electron acceptors in a series of redox reactions ending in oxygen, whose reactions releases half of the total of energy in eukaryotes have redox reactions are catalyzed by a series of complexes within the inner membranes of the cell's mitochondria.