Sterols

Sterols are derived lipids — built not directly from glycerol and fatty acids but by further modification, and structurally quite different from the other lipid classes. A sterol molecule consists of a rigid system of four fused hydrocarbon rings (the 'steroid nucleus') carrying a long hydrocarbon side chain.

Cholesterol is the most familiar sterol. It occurs throughout the animal body, and is particularly abundant in nervous tissue, existing either free or combined as a cholesterol ester. Several important biological molecules are synthesised from cholesterol, including the adrenocorticoid hormones, the sex hormones (progesterone, testosterone) and vitamin D. …