Asterol is anyorganic compound with askeleton closely related tocholestan-3-ol and having a hydroxyl group at carbon 3. The simplest sterol isgonan-3-ol, which has a formula ofC
17H
28O, and is derived from that ofgonane by replacement of ahydrogen atom on C3 position by ahydroxyl group. It is therefore analcohol of gonane.[1][2][3]
More generally, any compounds that contain the gonane structure, additionalfunctional groups, and/or modified ring systems derived from gonane are calledsteroids. Therefore, sterols are a subgroup of the steroids. They occur naturally in mosteukaryotes, includingplants,animals, andfungi, and can also be produced by somebacteria (however likely with different functions).[4][5] The most familiar type of animal sterol ischolesterol, which is vital to the structure of thecell membrane, and functions as a precursor to fat-solublevitamins andsteroid hormones. While technically alcohols, sterols are classified bybiochemists aslipids (fats in the broader sense of the term).
Some sources make a distinction betweensterols andstanols. In this context, the difference between them is analogous to the difference betweencholesterol andcholestanol, in that sterols have a double bond between C-5 and C-6, while stanols have not.[6][a]
Phytosterols are sterols naturally found inplants. Notable examples of phytosterols includecampesterol,sitosterol, andstigmasterol.
Zoosterols are sterols found inanimals. The most significant zoosterol ischolesterol.
Sterols found infungi are called mycosterols. A common example isergosterol, a mycosterol present in thecell membrane of fungi, where it serves a role similar to cholesterol in animal cells.
Sterols and related compounds play essential roles in the physiology ofeukaryotic organisms, and are essential for normal physiology of plants, animals, and fungi.[8] For example, cholesterol forms part of the cellular membrane in animals, where it affects the cell membrane's fluidity and serves assecondary messenger in developmental signaling. In humans and other animals,corticosteroids such ascortisol act as signaling compounds in cellular communication and general metabolism. Sterols are common components ofhuman skin oils.[9]
Phytosterols, 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.[10] They are currently approved by the U.S.Food and Drug Administration for use as afood supplement; however, there is some concern that they may block absorption not only of cholesterol, but of other important nutrients as well. At present, theAmerican 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.[11]Functional foods enriched with plant sterols/stanols have become the most widely used nonprescription cholesterol-lowering approach.[12] Preliminary research has shown that phytosterols may have anticancer effects.[13]
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Sterols are a subgroup ofsteroids with ahydroxyl group at the 3-position of the A-ring.[14] They areamphipathiclipids synthesized fromacetyl-coenzyme A via theHMG-CoA reductase pathway. Sterols are not flat, because they have several carbon atoms that have single bonds to three other carbon atoms and are therefore tetrahedralchiral centres. Only certainstereoisomers occur in nature. The hydroxyl group on the A ring ispolar. The rest of thealiphatic chain isnon-polar.
Natural products derived from the steroid skeleton and containing a hydroxy group in the 3 position, closely related to cholestan-3-ol.
The Fluidity of a Lipid Bilayer Depends on Its Composition
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