Lipids are organic molecules that are soluble in organic solvents such as chloroform and methanol and insoluble in water. Th e word lipid is derived from the Greek work ‘lipos’ meaning fat. Th ey are the principal components of cell membranes. In addition, they also act as energy source for living systems. Fat provide 2-3 fold higher energy compared to carbohydrates / proteins.

14.3.1 Classification of lipids:

Based on their structures lipids can be classified as simple lipids, compound lipids and derived lipids. Simple lipids can be further classified into fats, which are esters of long chain fatty acids with glycerol (triglycerides) and waxes which are the esters of fatty acids with long chain monohydric alcohols (Bees wax).

Compound lipids are the esters of simple fatty acid with glycerol which contain additional groups. Based on the groups attached, they are further classified into phospholipids, glycolipids and lipoproteins. Phospholipids contain a phospho-ester linkage while the glycolipids contain a sugar molecule attached. The lipoproteins are complexes of lipid with proteins.

14.3.2 Biological importance of lipids

1.Lipids are the integral component of cell membrane. They are necessary of structural integrity of the cell.

2.The main function of triglycerides in animals is as an energy reserve. They yield more energy than carbohydrates and proteins.

3.They act as protective coating in aquatic organisms.

4.Lipids of connective tissue give protection to internal organs.

5.Lipids help in the absorption and transport of fat soluble vitamins.

6.They are essential for activation of enzymes such as lipases.

7.Lipids act as emulsifier in fat metabolism.