24-ethyl-lanostane, a hypothetical<unk>  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<unk>  is a biologically active organic compound with four rings arranged in a specific molecular configuration.<unk> s have two principal biological functions: as important components of cell membranes which alter membrane fluidity; and as signaling molecules. Hundreds of<unk> s are found in plants, animals and fungi. All<unk> s are manufactured in cells from the sterols lanosterol (opisthokonts) or cycloartenol (plants). Lanosterol and cycloartenol are derived from the cyclization of the triterpene squalene. The<unk>  core structure is typically composed of seventeen carbon atoms, bonded in four "fused" rings: three six-member cyclohexane rings (rings A, B and C in the first illustration) and one five-member cyclopentane ring (the D ring).<unk> s vary by the functional groups attached to this four-ring core and by the oxidation state of the rings. Sterols are forms of<unk> s with a hydroxy group at position three and a skeleton derived from cholestane.<unk> s can also be more radically modified, such as by changes to the ring structure, for example, cutting one of the rings. Cutting Ring B produces secosteroids one of which is vitamin D3. Examples include the lipid cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.
Steroid
Antibiotic
Antimicrobial
Steris
Analgesic
Antipyretic
Broad-spectrum antibiotic
Antiparasitic