Classification of lipids

 Classification of lipids:-

Lipids are broadly classified (modified from Bloor) into simple, complex,

derived and miscellaneous lipids, which are further subdivided into different

groups

1. Simple lipids : Esters of fatty acids with alcohols. These are mainly of two

types

(a) Fats and oils (triacylglycerols) : These are esters of fatty acids with

glycerol. The difference between fat and oil is only physical. Thus, oil

is a liquid while fat is a solid at room temperature.

(b) Waxes : Esters of fatty acids (usually long chain) with alcohols other

than glycerol. These alcohols may be aliphatic or alicyclic. Cetyl

alcohol is most commonly found in waxes. Waxes are used in the

preparation of candles, lubricants, cosmotics, ointments, polishes etc.

2. Complex (or compound) lipids : These are esters of fatty acids with alcohols

containing additional groups such as phosphate, nitrogenous base,

carbohydrate, protein etc. They are further divided as follows

(a) Phospholipids : They contain phosphoric acid and frequently a

nitrogenous base. This is in addition to alcohol and fatty acids.

(i) Glycerophospholipids : These phospholipids contain glycerol as

the alcohol e.g., lecithin, cephalin.

(ii) Sphingophospholipids : Sphingosine is the alcohol in this

group of phospholipids e.g., sphingomyelin.

(b) Glycolipids : These lipids contain a fatty acid, carbohydrate and

nitrogenous base. The alcohol is sphingosine, hence they are also

called as glycosphingolipids. Glycerol and phosphate are absent e.g.,

cerebrosides, gangliosides.

(c) Lipoproteins : Macromolecular complexes of lipids with proteins.

(d) Other complex lipids : Sulfolipids, aminolipids and lipopolysaccharides

are among the other complex lipids.

3. Derived lipids : These are the derivatives obtained on the hydrolysis of group

1 and group 2 lipids which possess the characteristics of lipids. These include

glycerol and other alcohols, fatty acids, mono-and diacylglycerols, lipid (fat)soluble vitamins, steroid hormones, hydrocarbons and ketone bodies.

4. Miscellaneous lipids : These include a large number of compounds

possessing the characteristics of lipids e.g., carotenoids, squalene,

hydrocarbons such as pentacosane (in bees wax), terpenes etc.