Lipid substances, containing a phosphate
group and one or more fatty acid residues, which are essential
components of cell membranes. Hydrolysis yields fatty acids,
phosphoric acid, and a base. They are amphoteric with a polar
and a nonpolar region. Lecithins, cephalins, and related com_x0002_pounds are based on a glycerol backbone, with a phosphate
group. In lecithin (phosphatidylcholine), R0 and Rv are fatty
acid residues, usually one saturated and the other unsaturated.
In the cephalins, ethanolamine (H2NCH2CH2OH) or serine
replaces choline. They are used in the food industry as surfactants, emulsifiers, and antioxidants. In sphingomyelins, R is a
fatty acid residue, usually tetracosanoic acid. They occur abundantly in brain tissues in association with cerebrosides, which
are similar. On hydrolysis they split into choline, sphingosine,
phosphoric acid, and a fatty acid.
