LIPIDS

Lipids are heterogenous group of compounds (an important biomolecules) that can be extracted from cells (tissues) by non polar solvent i.e  they are sparingly soluble in water and readily soluble  in organic solvents like benzene, ether, chloroform. They include fats, oil, fatty acids, phospholipids, glycolipids, steroids and terpenes.

Many classifications available but mostly Bloor’s classification is mentioned.  Bloor in 1943 classified Lipids on the basis of chemical structure.

Simple Lipids (Homolipids)

Fats and Oils, Waxes 

Chemically Fats are esters of glycerols (alcohols) and fatty acids. They are therefore called as triglycerides or triacylglycerol (commonly called). Fats are solids and oils are liquids in ordinary room temperature. Waxes are  esters of fatty acids with high molecular weight monohydroxy alcohols.

Compound Lipids (Heterolipids)

They are also esters of alcohols and fatty acids but possess an additional group. They are also called polar lipids.

Phospholipids

These are compounds containing in addition to fatty acids and glycerol, a phosphoric  acid, nitrogenos bases and other compounds

Glycolipids

These are compounds of fatty acids with carbohydrates and contain nitrogen but no phosphoric acid. The glycolipids also contain structurally related compounds containing groups like gangliosides, sulfolipids and sulfatides.

Derived Lipids

Derived lipids are “catch all” group in Bloor’s classification. They are derived from simple and compound lipids. i.e They include hydrolysis products of simple and compound lipids and various other compounds such as steroids, terpenes, fatty acids, alcohols, fatty aldehydes, ketones etc. 

Biological Importance of Lipids

• Lipids are an important class of Biomolecules. They play an indispensible role. Some of their important functions as follows.
• They serve as a source of food with high calorific value. 1gm of lipid give 9.3 kilocalories.
• They are insoluble in aqueous solution and hence can be stored readily in the body as a food reserve.
• They are important constituents of all the cell membrane in the form of lipoprotein.
• Fats (Lipids) are characterized for their heat insulating capacity. Antarctic animals have a thick layer of adipose tissue under their skin which enables them to tolerate the cold climate of these areas.
• Plants of arid zone have a thin layer of waxes on their leaves which prevent the stomatal transpiration.
• A thick layer of adipose tissue is present around certain delicate organs such as kidney which protects them from physical shock.
• They act as carrier of natural fat soluble vitamins such as vitamin A, D and E.