Fatty acid breakdown brings about the oxidation of long-chain fatty acids. The fatty acids are first transformed to their acyl CoA (coenzyme A) derivatives and then degraded by the successive removal of two-carbon units from the end of the fatty acid as acetyl CoA. The pathway makes FADH2   and NADH directly. The acetyl CoA generates can also enter the citric acid cycle and make further NADH and FADH2. The NADH and FADH2 are then oxidized by the respiratory electron transport chain to yield energy in the shape of ATP.