Figure 1: Schematic outline of the metabolic steps of utilization of glucose and fatty acids in the mitochondria: reduction of FAD/NAD+ to FADH2/NADH by Krebs cycle and beta oxidation, oxidation of FADH2/NADH to gain back FAD/ NAD+ in the electron transport chain by inner membrane complexes I, III and IV that also produce the proton gradient over the inner membrane and H2O, the inner membrane ATP synthase that utilizes proton inner membrane gradient directed flow to convert ADP to ATP. Uncoupling inner membrane proteins (UCPs) facilitate gradient directed proton "leak" through the inner membrane.