ABSTRACT
Cholesterol is a steroid. It is an important constituent of cell membranes, where, in mammals, it modulates their fluidity. Cholesterol is also the precursor of steroid hormones such as progesterone, testosterone and cortisol, and the bile salts. Animals are able to synthesize cholesterol de novo by an elegant series of reactions in which all 27 carbon atoms of cholesterol are derived fromacetyl CoA. Cholesterol can be obtained either from the diet or it can be synthesized de novo, mainly in the liver. Cholesterol is transported round the body inlipoprotein particles. The rate of synthesis of cholesterol is dependent on the cellular level of cholesterol. Bile salts are polar derivatives of cholesterol and constitute the major pathway for the excretion of cholesterol in mammals. Cholesterol is the precursor of the five major classes of steroid hormones.
