Triglycerides

A triglyceride is made of one glycerol molecule joined to three fatty acids. Fats and oils are triglycerides.Each fatty acid joins to one of the three –OH groups of glycerol in a condensation reaction. The –OH of glycerol reacts with the –COOH of the fatty acid, a molecule of water is released, and an ester bond forms. Three fatty acids give three ester bonds and release three water molecules:glycerol + 3 fatty acids → triglyceride + 3 H₂OThe reverse reaction is hydrolysis: adding three water molecules breaks the ester bonds, releasing glycerol and fatty acids. In digestion this is catalysed by lipase.The three fatty acids in a triglyceride can be the same or different, so there are many different triglycerides.How the structure suits energy storage:
• the long hydrocarbon chains contain many C–H bonds, so triglycerides release about twice as much energy per gram as carbohydrates
• they are insoluble and non-polar, so they do not affect water potential and are stored as droplets in the cytoplasm
• a lot of energy is stored in a small mass, useful for animals that move and for seeds
• oxidation releases metabolic water, important for desert animals such as camelsWorked example: glycerol (M_r = 92) joins three stearic acid molecules (M_r = 284). The M_r of the triglyceride is 92 + 3 × 284 − 3 × 18 = 890.