Sterol

A sterol is any organic compound with a skeleton closely related to cholestan-3-ol and having a hydroxyl group at carbon 3. The simplest sterol is gonan-3-ol, which has a formula of C17H28O, 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. More generally, any compounds that contain the gonane structure, additional functional groups, and/or modified ring systems derived from gonane are called steroids. 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 (but likely with different functions). The most familiar type of animal sterol is cholesterol, which is vital to the structure of the cell membrane, and functions as a precursor to vitamin D and steroid hormones. While technically alcohols, sterols are classified by biochemists as lipids (fats in the broader sense of the term). 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 an unsaturated gonane skeleton, while stanols do not.