Tuesday 7 October 2003
Definition: Sterols are also known as steroid alcohols. They are a subgroup of steroids with a hydroxyl group at the 3-position of the A-ring.
Sterols are an important class of organic molecules. They occur naturally in plants, animals and fungi, with the most familiar type of animal sterol being cholesterol.
Sterols of plants are called phytosterols and sterols of animals are called zoosterols.
Important zoosterols are cholesterol and some steroid hormones; notable phytosterols include campesterol, sitosterol, and stigmasterol. Ergosterol is a sterol present in the cell membrane of fungi, where it serves a role similar to cholesterol in animal cells.
Sterols are amphipathic lipids synthesized from acetyl-coenzyme A via the HMG-CoA reductase pathway. The overall molecule is quite flat. The hydroxyl group on the A ring is polar. The rest of the aliphatic chain is non-polar.
Other examples of sterols are the bile acids and their conjugates, which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver.
Sterols and related compounds play essential roles in the physiology of eukaryotic organisms.
Sterol lipids, such as cholesterol and its derivatives are an important component of membrane lipids, along with the glycerophospholipids and sphingomyelins.
Cholesterol forms part of the cellular membrane in animals, where it affects the cell membrane’s fluidity and serves as second messenger in developmental signaling.