Lipids
Lipids are oily or greasy organic compound forming about 3% of protoplasm. These are also compound of carbon hydrogen and oxygen but unlike carbohydrates. The hydrogen and oxygen, in them 2:1 ratio the amount of oxygen is considerably less. Being insoluble in water and soluble in organic solvents like acetone, chloroform benzene, hot alcohols ether, kerosene, petroleum, etc, lipids occur in protoplasm as minute globules.
The simplest and most abundant lipids are neutral or true fats, called simple lipids. These are esters of long chain fatty acids and glycerol. Each fat molecule is formed by combination of usually three fatty acid molecules linked with one molecule of glycerol and hence it is called a triglyceride. This linkage is called ester bond three molecules of water are released in it. Hence this is also a compensation dehydration synthesis. A fatty acid molecule is no polar with a single, water soluble carboxylic acid group (COOH) and a long, water insoluble hydrocarbon chain, the latter may be fully saturated or unsaturated. Fatty acids are of several kinds, but two of these viz, palmitic acid and oleic acid are the parent compounds respectively of all saturated and unsaturated fatty acids. Being synthesized by joining of two carbon acetyl units, nearly all fatty acids have an even number of carbon atoms from 2 to 24 similar or different fatty acids may participate in the composition of a fat molecule.