sterol

n.
Any of a group of predominantly unsaturated solid alcohols of the steroid group, such as cholesterol and ergosterol, present in the fatty tissues of plants and animals.

[Short for CHOLESTEROL.]

Any of a group of naturally occurring or synthetic organic compounds with a steroid ring structure, having a hydroxyl (OH) group, usually attached to carbon-3. This hydroxyl group is often esterified with a fatty acid (for example, cholesterol ester). The hydrocarbon chain of the fatty-acid substituent varies in length, usually from 16 to 20 carbon atoms, and can be saturated or unsaturated. Sterols commonly contain one or more double bonds in the ring structure and also a variety of substituents attached to the rings. Sterols and their fatty-acid esters are essentially water insoluble. For transport in an aqueous milieu (for example, the bloodstream of mammals), sterols and other lipids are bound to specific proteins, forming lipoprotein particles. These particles are classified based on their composition and density. One lipoprotein class is abnormally high in the blood of humans prone to heart attacks.

Sterols are widely distributed in nature. Modifications of the steroid ring structure are made by specific enzyme systems, producing the sterol characteristic for each species, such as ergosterol in yeast. The major regulatory step in the sterol biosynthetic pathway occurs early in the process. Drugs that lower blood cholesterol levels in humans are designed to inhibit this regulatory enzyme. In addition to their conversion to sterols, several intermediates in the pathway are precursors of other important biological compounds, including chlorophyll in plants, vitamins A, D, E, and K, and regulators of membrane functions and metabolic pathways.

A universal role of sterols is to function as part of membrane structures. In addition, some insects require sterols in their diets. Cholesterol also serves as a precursor of steroid hormones (estrogens, androgens, glucocorticoids, and mineralocorticoids) and bile acids. See also Cholesterol; Steroid.

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Alcohols derived from the steroids; including cholesterol, ergosterol in yeast (the precursor for synthetic vitamin D₂), sitosterol and stigmasterol in plants, and coprosterol in faeces.

(ster′ôlz)
n.pl

Steroids having one or more hydroxyl groups and no carbonyl or carboxyl groups (for example, cholesterol).

A group of chemicals derived from steroids. They include cholesterol and the several compounds which make up vitamin D.

Any steroid, e.g. cholesterol and ergosterol, having long (8–10 carbons) aliphatic side-chains at position 17 and at least one alcoholic hydroxyl group; the sterols have lipid-like solubility.

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