Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy which is used to produce adenosine triphosphate (ATP). In most eukaryotes, this takes place inside the mitochondria, in the inner mitochondrial membrane. In aerobic organisms, oxidative phosphorylation is the major source of ATP.
NAD are required as hydrogen carriers during glycolysis and is heavily dependent on their availability. It takes place primarily in the cytoplasm of the cells.
The mitochondrial matrix also consists of enzymes which are required in Krebs' cycle.