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File:Steroid numbering.png

IUPAC recommended ring (left) and atom numbering (right) of the steroid skeleton.[1][2]


Steroid skeleton of lanosterol. The total number of carbons (30) reflects its triterpenoid origin.

File:Sterol synthesis.svg

Simplified version of the steroid synthesis pathway with the intermediates isopentenyl pyrophosphate(IPP),dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene shown. Some intermediates are omitted.

A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion. Steroids vary by the functional groups attached to these rings and the oxidation state of the rings. Hundreds of distinct steroids are found in plants, animals, and fungi. All steroids are made in cells either from the sterol lanosterol (animals and fungi) or the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene.[3]


Steroids include estrogen, cortisol, progesterone and testosterone. Estrogen and progesterone are made primarily in the ovary and in the placenta during pregnancy and testosterone in the testes. Testosterone is also converted into estrogen to regulate the supply of each, in the bodies of both females and males. Certain neurons and glia in the central nervous system (CNS) express the enzymes that are required for the local synthesis of pregnane neurosteroids, either de novo or from peripherally derived sources. The rate limiting step of steroid synthesis is the conversion of cholesterol to pregnenolone which occurs inside the mitochondrion.[4]



Some of the common categories of steroids:


It is also possible to classify steroids based upon their chemical composition. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples from this classification include:

Class Examples Number of carbon atoms
Cholstanes cholesterol 27
Cholanes cholic acid 24
Pregnanes progesterone 21
Androstanes testosterone 19
Estranes estradiol 18

See also


  1. (December 1989)IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN). The nomenclature of steroids. Recommendations 1989. Eur. J. Biochem. 186 (3): 429–58.
  2. G. P. Moss (1989). Nomenclature of Steroids (Recommendations 1989). Pure & Appl. Chem. 61 (10): 1783–1822.
  3. Lanosterol biosynthesis
  4. Rossier MF (2006). T channels and steroid biosynthesis: in search of a link with mitochondria. Cell Calcium. 40 (2): 155–64.

External links

Template:Biochemical families
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