Lipids, amino acids and proteins

Lipids are a group of organic compounds that do not dissolve in water. The most common are simple lipids, the neutral fats: fats in animals and oils in plants (liquid at ordinary temperature); chemically they are built of glycerol and fatty acids. Wax is also a simple lipid and forms a water-proof coating (for example on leaves and in a honeycomb). Complex lipids: phospholipids are the basis of the cell membrane, and glycolipids and lipoproteins (lipid + protein) are important for membranes and transport. Steroids (cholesterol, sex hormones, vitamin D) are another group of lipids. The functions of lipids: energy (1 g of fat fully broken down gives about 38.9 kJ, nearly twice as much as carbohydrate), storage, heat insulation (fat under the skin), building membranes, making hormones and protection. When fat is oxidised, water is also formed (about 1.1 L from 1 kg of fat): this metabolic water helps desert animals, while the fat in a camel’s hump is first of all an energy reserve.