Sterol is an organic compound with formula , whose molecule is derived from that of

gonane Gonane is a chemical compound with formula , whose molecule can be described as three molecules or entities of cyclohexane and one of cyclopentane, fused in a particular way. More specifically, the molecule can be described as that of cyclohe ...

by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

of gonane. More generally, any compounds that contain the gonane structure, additional functional groups, and/or modified ring systems derived from gonane are called

steroids A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

. Therefore, sterols are a subgroup of the steroids. They occur naturally in most eukaryotes, including plants, animals, and fungi, and can also be produced by some bacteria (however likely with different functions). The most familiar type of animal sterol is cholesterol, which is vital to cell membrane structure, and functions as a precursor to fat-soluble vitamins and steroid hormones. While technically alcohols, sterols are classified by

biochemist Biochemists are scientists who are trained in biochemistry. They study chemical processes and chemical transformations in living organisms. Biochemists study DNA, proteins and Cell (biology), cell parts. The word "biochemist" is a portmanteau of ...

s as lipids ( fats in the broader sense of the term). Steran_num_ABCD

Types

Sterols of plants are called '' phytosterols'' and sterols of animals are called ''zoosterols''. The most important zoosterol is cholesterol; notable phytosterols include campesterol,

sitosterol β-sitosterol (beta-sitosterol) is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. It is a white, waxy powder with a characteristic odor, and is one of the components of the food additive E499. ...

, and stigmasterol.

Ergosterol Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in cell membranes of fungi and protozoa, serving many of the same functions that cholesterol serves in animal cells. Because many fungi and protozoa cannot survive without ergosterol, the ...

is a sterol 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 eukaryotic organisms. 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 Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involve ...

such as

cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...

act as signaling compounds in cellular communication and general metabolism. Sterols are common components of human skin oils.

Phytosterols as a nutritional supplement

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. 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 The American Heart Association (AHA) is a nonprofit organization in the United States that funds cardiovascular medical research, educates consumers on healthy living and fosters appropriate cardiac care in an effort to reduce disability and death ...

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. Preliminary research has shown that phytosterols may have anticancer effects.

Chemical classification and structure

Sterols are a subgroup of

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

s with a

hydroxyl group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy g ...

at the 3-position of the A-ring. They are amphipathic lipids synthesized from acetyl-coenzyme A via the

HMG-CoA reductase HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, official symbol HMGCR) is the rate-controlling enzyme (NADH-dependent, ; NADPH-dependent, ) of the mevalonate pathway, the metabolic pathway that produces cholesterol and oth ...

pathway. The overall molecule is quite flat. The hydroxyl group on the A ring is

polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...

. The rest of the aliphatic chain is non-polar.

References

External links

Sterols
Cyberlipid.org {{Authority control