The answer is beta oxidation. It is a process in which molecules particularly fatty acids are cracked down in the prokaryotes’ cytosol and in the mitochondria in eukaryotes to produce acetyl-CoA, which goes in the citric acid cycle, FADH2, and NADH which are co-enzymes that are cast-off in the electron transport chain. The major response site is the beta-carbon from the thioester carbon.