Lipids are the esters of higher fatty acid with alcohol, such as glycerol, etc. These can be classified as
1. Simple Lipids are esters of fatty acids with alcohol. These may be
(i) Fats These are esters of higherfatty acids with glycerol (triglycerides).
(ii) Waxes These are esters of higher fatty acids with alcohol other than glycerol.
2. Compound or conjugated lipids, are those compounds which contain simple lipids and prosthetic (other additional) group. They include
(i) Glycerophospholipids, also known as phospholipids in which one of the fatty acid is replaced by phosphoric acid which is linked to nitrogenous groups like choline, ethanolamine, serine ete, e.g., Lecithin and cephalin, etc.
(ii) Sphingo lipids, are lipides having phosphoric acid with amine alcohol 4-sphinganine or sphingosine instead of glycerol in addition to fatty acid and choline.
(iii) Glycolipids, i.e, those which contain spinganine with a fatty acid and a monosaccharide sugar, e.g., cerebrosides and gangliosides.
3. Steroids are compounds with different chemical nature but similar physical properties, Their structure is based upon a 4 ring cyclopentenoperhydro phenanthrene, e.g., cholesterol.
4. Prostoglandins are derivatives of arachidonic acid and contain 20 C-atoms. These are biologically active lipids.