Simple Lipids

Simple lipids are esters of fatty acids with various alcohols; fats and waxes are the two main kinds.

Fats are esters of fatty acids with the three-carbon alcohol glycerol (CH₂OH–CHOH–CH₂OH). A triglyceride — the typical fat molecule — consists of one glycerol molecule esterified to three fatty-acid molecules. Fats built mainly from unsaturated fatty acids tend to be liquid at room temperature and are then called oils; unsaturated fats can be converted to solid fats by hydrogenating (adding hydrogen across) their double bonds — the industrial process that gives products such as vanaspati ghee.

Fats are a concentrated, high-calorific-value nutritional reserve. In plants, fat is stored in seeds to nourish the embryo during germination; in animals, it is stored in the adipocytes of adipose tissue. Fat deposited under the skin (subcutaneous fat) acts as an insulator, cutting down loss of body heat, while fat deposited around internal organs cushions them, absorbing mechanical shock. …