General Veterinary Biochemistry

STEROIDS

• Steroids are generally considered along with lipids.
• All of the steroids have a common basic ring structure called CPPP nucleus or cyclopentanoperhydrophenanthrene .
• It contains 4 fused rings, 3 with six membered rings and one with five membered rings. The 3 six membered rings (A, B and C) resembles phenanthrene, attached to the 5 membered ring resembling cyclopentane ring (D).
• However, the rings are not uniformly unsaturated. The rings are also not benzene rings.
• The positions on the steroid nucleus are numbered as shown in the figure. Methyl side chains are shown by single bonds. These occur at positions 10 and 13 (constituting C atoms 19 and 18 respectively).
• A side chain is seen at position 17 (as in cholesterol).
• If the compound has one or more hydroxyl groups and no carbonyl or carboxyl groups, it is a sterol, and the name terminates in – ol.