The outer membrane of the mitochondrium is freely permeable to all metabolites. A shuttle system transports electrons from cytosolic NADH to NAD in the matrix. Oxygen diffuses into the matrix and carbon dioxide diffuses out. Oxidation of pyruvate in the citric acid cycle generates NADH and FADH2. Electrons from these reduced coenzymes are transferred via four electron transport complexes to oxygen comitant with transport of hydrogen ion from the matrix to the inter membrane space, generating the proton-motive force.
Citric acid is isomerized to isocitric acid.
Two major events occur during this step. Isocitric acid loses carbon dioxide leaving a five-carbon molecule. A multienzyme complex catalyzes. Removal of carbon dioxide. The high energy bond is succinyl-CoA breaks, and some energy is conserved as CoA is displaced by a phosphate group.