Classification Of Lipids
According to one scheme lipids are classified as Simple Lipids, Compound (conjugated ) Lipids and Steroids.
(A) SIMPLE LIPIDS : These are esters of fatty acids with alcohols.
(1) FATS are esters of fatty acids with glycerol.
(2) WAXES are esters of high MW fatty acids with alcohols other than glycerol (true waxes) or with sterols (steryl esters).
(B) COMPOUND LIPIDS on hydrolysis yield in addition to alcohol and fatty acids, other groups. They include
(1) GLYCEROPHOSPHOLIPIDS. Phosphoric acid and usually two fatty acids esterified to glycerol, e.g. phosphatidic acids, lecithins and cephalins.
(2) SPHINGOPHOSPHOLIPIDS. contain the amine alcohol 4-spingenine instead of glycerol, in addition to a fatty acid, phosphoric acid and cholines.
(3) GLYCOLIPIDS on hydrolysis yield sphingenine , a fatty acid and a monosaccharide sugar (usually galactose). Other glycolipids ae cerebrosides and gangliosides.
(C) STEROIDS are included among lipids because of similar physical properties, although they have a different chemical structure based on a 4-ring cyclopentanoperhydrophenanthrene nucleus.
(D) PROSTAGLANDINS are derivatives of fatty acids and contain 20 carbon atoms.