Steroid

From Wikipedia, the free encyclopedia

Steroid skeleton of lanosterol. The total number of carbons (30) reflects its triterpenoid origin. In some steroids some carbons may be removed (such as carbon 18) or added (such as carbons 24¹ and 24²) in downstream biosynthetic reactions.

A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings. Different steroids vary in the functional groups attached to these rings. Hundreds of distinct steroids plants, animals, and fungi. All steroids are derived either from the sterol lanosterol (animals and fungi) or the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene.^[1]

[edit] Origin

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.

Steroids include estrogen (U.S spelling) or oestrogen (UK spelling), progesterone and androgen. Oestrogen and progesterone are made primarily in the ovary and in the placenta during pregnancy and testosterone in the testes. 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.

[edit] Classification

[edit] Taxonomical/Functional

Some of the common categories of steroids:

• Animal steroids
  • Insect steroids
    • Ecdysteroids such as ecdysterone
  • Vertebrate steroids
    • Sex steroids are a subset of sex hormones that produce sex differences or support reproduction. They include androgens, estrogens, and progestagens.
    • Corticosteroids include glucocorticoids and mineralocorticoids. Glucocorticoids regulate many aspects of metabolism and immune function, whereas mineralocorticoids help maintain blood volume and control renal excretion of electrolytes.
    • Anabolic steroids are a class of steroids that interact with androgen receptors to increase muscle and bone synthesis. There are natural and synthetic anabolic steroids. These are the steroids used by athletes to increase performance.
    • Cholesterol which modulates the fluidity of cell membranes and is the principle constituent of the plaques implicated in atherosclerosis.
• Plant steroids
  • Phytosterols
  • Brassinosteroids
• Fungus steroids
  • Ergosterols

[edit] Structural

It is also possible to classify steroids based upon their chemical composition. One example of how MeSH performs this classification is available at Wikipedia:MeSH D04#MeSH D04.808 --- steroids.

[edit] External links

• Michael W. King's Medical Biochemistry. Steroids and retinoids are both terpenes which are hydrophobic, pass through cell membranes and bind to intracellular receptors. However, retinoic acid is not a steroid because is does not have the defining ring structure. See: Steroids and Related Hydrophobic Molecules.
• "Biochemistry" by Jeremy M. Berg, John L. Tymoczko and Lubert Stryer (2002) W. H. Freeman and Co. steroid topics in this

[edit] References

1. ^ http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/terp/lanost.html

• Agis-Balboa RC. et al. (2006). "Characterization of brain neurons that express enzymes mediating neurosteroid biosynthesis". Proc Natl Acad Sci U S A 103, 14602-14607. PMID 16984997

• Belelli D. and Lambert JJ. (2005). "Neurosteroids: endogenous regulators of the GABA_A receptor". Nature Reviews Neuroscience 6, 565-575. PMID 15959466. Review

• Pinna G. et al. (2005). "Fluoxetine and norfluoxetine stereospecifically and selectively increase brain neurosteroid content at doses that are inactive on 5-HT reuptake". Psychopharmacology (Berl) 186, 362-372. PMID 16432684. Review

• Dubrovsky BO. (2005). "Steroids, neuroactive steroids and neurosteroids in psychopathology". Prog Neuropsychopharmacol Biol Psychiatry 29, 169-192, PMID 15694225. Review

• Mellon SH. and Griffin LD. (2002) "Neurosteroids: biochemistry and clinical significance". Trends Endocrinol Metab 13, 35-43. PMID 11750861. Review