Lipids form a group of organic compounds which are widely distributed in living organisms. Chemically they are esters of fatty acids or are capable of forming esters. The important lipids are triacyl glycerols, phospholipids, sterols and fatty acids.
Fatty acids are carboxylic acid with hydrocarbon side chains. They are the simplest form of lipids and they are water soluble. They exist in the body either as free acids or fatty acyl esters such as triacylglycerol. The fatty acids are released from these lipids on hydrolysis by lipases.
Fatty acids may be divided into (i) saturated fatty acids and (2) unsaturated fatty acids.