A sterol is any organic compound with a Skeletal formula closely related to Cholestanol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on C3 position by a hydroxyl group. It is therefore an alcohol of gonane.[ – The formula given is C19H31OR, with an R group attached at the sterol sidechain (C-17) position.][ – This source is more confusing, as it does not indicate an R group and simply uses gonan-3-ol for the structure of sterol. Nevertheless, the text clearly indicates that the name is intended for a larger group of compounds, and at no point is "sterol" intended as a synonym of gonan-3-ol.]
More generally, any compounds that contain the gonane structure, additional , and/or modified ring systems derived from gonane are called . Therefore, sterols are a subgroup of the steroids. They occur naturally in most Eukaryote, including , , and fungi, and can also be produced by some bacteria (however likely with different functions).
Some sources make a distinction between sterols and stanols. In this context, the difference between them is analogous to the difference between cholesterol and cholestanol, in that sterols have a double bond between C-5 and C-6, while stanols have not.
Types
Phytosterols
are sterols naturally found in
. Notable examples of phytosterols include
campesterol,
sitosterol, and
stigmasterol.
Zoosterols
Zoosterols are sterols found in
. The most significant zoosterol is
cholesterol.
Mycosterols
Sterols found in
fungi are called mycosterols. A common example is
ergosterol, a mycosterol present in the
cell membrane of fungi, where it serves a role similar to cholesterol in animal cells.
Role in biochemistry
Sterols and related compounds play essential roles in the physiology of
eukaryote organisms, and are essential for normal physiology of plants, animals, and fungi.
For example, cholesterol forms part of the cellular membrane in animals, where it affects the cell membrane's fluidity and serves as secondary messenger in developmental signaling. In humans and other animals,
corticosteroids such as
cortisol act as signaling compounds in cellular communication and general metabolism. Sterols are common components of
Sebum.
Phytosterols as a nutritional supplement
, more commonly known as plant sterols, have been shown in clinical trials to block cholesterol absorption sites in the human intestine, thus helping to reduce cholesterol absorption in humans.
They are currently approved by the U.S. Food and Drug Administration for use as a
food supplement; however, there is some concern that they may block absorption not only of cholesterol, but of other important nutrients as well. At present, the American Heart Association has recommended that supplemental plant sterols be taken only by those diagnosed with elevated cholesterol, and has particularly recommended that they not be taken by pregnant women or nursing mothers.
Functional foods enriched with plant sterols/stanols have become the most widely used nonprescription cholesterol-lowering approach.
Preliminary research has shown that phytosterols may have anticancer effects.
Chemical classification and structure
Sterols are a subgroup of
with a
hydroxyl group at the 3-position of the A-ring.
They are
amphipathic 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.
See also
Further reading
External links
