Steroid

This article is about the family of polycyclic compounds. For the drugs, also used as performance-enhancing substances, see Anabolic steroid. For the scientific journal, see Steroids (journal). For the Death Grips EP, see Steroids (Crouching Tiger Hidden Gabber Megamix).

Structure of 24-ethyl-lanostane, a prototypical steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC-approved ring lettering and atom numbering.

A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration.

Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and as signaling molecules. Examples include the lipid cholesterol, sex hormones estradiol and testosterone, anabolic steroids, and the anti-inflammatory corticosteroid drug dexamethasone. Hundreds of steroids are found in fungi, plants, and animals. All steroids are manufactured in cells from sterol precursors: cholesterol and lanosterol (in opisthokonts), or cycloartenol (in plants). All three of these molecules are produced via cyclization of the triterpene squalene.