fatty acid metabolism A fatty acid is composed of a terminal carboxylate group and a long hydrocarbon chain. Fatty acids exert four major physiological roles in the organism. Firstly, fatty acids serve as building blocks of amphipathic molecules such as phospholipids and glycolipids, which are important components of biological membranes. Secondly, fatty acids can target many proteins to membrane locations by covalently attached to the targeted proteins. Thirdly, stored as triacylglycerols, uncharged esters of fatty acids with glycerol, fatty acids are the preferred fuel molecules for the heart and the preferred energy source for skeletal muscle at the time of prolonged exertion. Triacylglycerols are catabolized into free fatty acid and glycerol. In the liver and peripheral, through β-oxidation, free fatty acid is metabolized into acetyl CoA while glycerol is used for gluconeogenesis or triglyceride regeneration. Finally, fatty acid derivatives act as intracellular messengers and hormones.