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.[1][2][3]

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).[4][5] 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.[6][lower-alpha 1]

The gonane skeleton, with the IUPAC recommended numbering of the carbon atoms

## Contents

* 1 Types
* 1.1 Phytosterols
* 1.2 Zoosterols
* 1.3 Mycosterols
* 2 Role in biochemistry
* 2.1 Phytosterols as a nutritional supplement
* 3 Chemical classification and structure
* 4 See also
* 5 References
* 6 Further reading
* 7 External links

## Types

### Phytosterols

Phytosterols are sterols naturally found in plants. Notable examples of phytosterols include campesterol, sitosterol, and stigmasterol.

### Zoosterols

Zoosterols are sterols found in animals. The most significant zoosterol is cholesterol.

### Mycosterols

Sterols found in fungi are called mycosterols. A common example is ergosterol, a mycosterol present in the cell membrane of fungi, where it serves a role similar to cholesterol in animal cells.

## Role in biochemistry

Sterols and related compounds play essential roles in the physiology of eukaryotic organisms, and are essential for normal physiology of plants, animals, and fungi.[8] For example, cholesterol forms part of the cellular membrane in animals, where it affects the cell membrane's fluidity and serves as secondary messenger in developmental signaling. In humans and other animals, corticosteroids such as cortisol act as signaling compounds in cellular communication and general metabolism. Sterols are common components of human skin oils.[9]

### Phytosterols as a nutritional supplement

Main articles: Chemistry:Phytosterol and Phytostanol

Phytosterols, more commonly known as plant sterols, have been shown in clinical trials to block cholesterol absorption sites in the human intestine, thus helping to reduce cholesterol absorption in humans.[10] They are currently approved by the U.S. Food and Drug Administration for use as a food supplement; however, there is some concern that they may block absorption not only of cholesterol, but of other important nutrients as well. At present, the American Heart Association has recommended that supplemental plant sterols be taken only by those diagnosed with elevated cholesterol, and has particularly recommended that they not be taken by pregnant women or nursing mothers.[11] Functional foods enriched with plant sterols/stanols have become the most widely used nonprescription cholesterol-lowering approach.[12] Preliminary research has shown that phytosterols may have anticancer effects.[13]

## Chemical classification and structure

Sterols are a subgroup of steroids with a hydroxyl group at the 3-position of the A-ring.[14] They are amphipathic lipids synthesized from acetyl-coenzyme A via the HMG-CoA reductase pathway. Sterols are not flat, because they have several carbon atoms that have single bonds to three other carbon atoms and are therefore tetrahedral chiral centres. Only certain stereoisomers occur in nature. The hydroxyl group on the A ring is polar. The rest of the aliphatic chain is non-polar.

There are multiple ways to classify sterols, including by:[15]

* Source or origin of sterol. Sterols can be found in animals (zoosterols), plants (phytosterols), and fungi (mycosterols).
* Methyl group presence on C-4. This carbon can exhibit 0, 1, or 2 methyl groups, known as 4-desmethyl, 4α-monomethyl, and 4,4-dimethyl sterols, respectively.
* Side chain presence on C-24. Examples include 24-desmethyl (e.g. cholesterol), 24-methyl (e.g. campesterol), and 24-ethyl (e.g. stigmasterol or β-sitosterol).
* Unsaturation of sterol. Double bonds are common at the 5,6-position (termed Δ5 sterols, e.g. cholesterol), the 7,8-position (termed Δ7 sterols, e.g. lathosterol), or both (termed Δ5,7 sterols, e.g. ergosterol and 7-dehydrocholesterol).

## See also

* Cholesterol
* Ergosterol
* Hopanoids
* Hydroxysteroid
* Phytosterol
* Steroids
* Zoosterol
* Zymosterol

## References

1. ↑ The word stenol exists to exclusively refer to a sterol with a double bond in the main rings. However, usage of this word is rare outside of compounds such as cholestenol.[7]

1. ↑ "sterol (CHEBI:15889)". https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:15889. - The formula given is C19H31OR, with an R group attached at the sterol sidechain (C-17) position.
2. ↑ "Sterols (1107)" (in en). https://pubchem.ncbi.nlm.nih.gov/compound/1107. - This source is more confusing, as it does not indicate an R group and simply uses gonan-3-ol for the structure of sterol. Nevertheless, the text clearly indicates that the name is intended for a larger group of compounds, and at no point is "sterol" intended as a synonym of gonan-3-ol.
3. ↑ The International Union of Pure and Applied Chemistry (IUPAC). "IUPAC - sterols (S06006)" (in en). https://goldbook.iupac.org/terms/view/S06006. "Natural products derived from the steroid skeleton and containing a hydroxy group in the 3 position, closely related to cholestan-3-ol."
4. ↑ "Sterol Synthesis in Diverse Bacteria". Frontiers in Microbiology 7: 990. 24 June 2016. doi:10.3389/fmicb.2016.00990. PMID 27446030.
5. ↑ "Evolution of bacterial steroid biosynthesis and its impact on eukaryogenesis". Proceedings of the National Academy of Sciences of the United States of America 118 (25). June 2021. doi:10.1073/pnas.2101276118. PMID 34131078. Bibcode: 2021PNAS..11801276H.
6. ↑ Cantrill, Richard (2008). "PHYTOSTEROLS, PHYTOSTANOLS AND THEIR ESTERS Chemical and Technical Assessment". https://www.fao.org/fileadmin/templates/agns/pdf/jecfa/cta/69/Phytosterols.pdf.
7. ↑ "stenol, n. meanings, etymology and more". https://www.oed.com/dictionary/stenol_n.
8. ↑ Luo, Jie; Yang, Hongyuan; Song, Bao-Liang (April 2020). "Mechanisms and regulation of cholesterol homeostasis" (in en). Nature Reviews Molecular Cell Biology 21 (4): 225–245. doi:10.1038/s41580-019-0190-7. ISSN 1471-0080. PMID 31848472. https://www.nature.com/articles/s41580-019-0190-7.
9. ↑ "Human stratum corneum lipids: characterization and regional variations". Journal of Lipid Research 24 (2): 120–30. February 1983. doi:10.1016/S0022-2275(20)38005-6. PMID 6833889.
10. ↑ "Inhibition of cholesterol absorption by phytosterol-replete wheat germ compared with phytosterol-depleted wheat germ". The American Journal of Clinical Nutrition 77 (6): 1385–9. June 2003. doi:10.1093/ajcn/77.6.1385. PMID 12791614.
11. ↑ "Do we need to be buying plant sterols?". Food Magazine 67: 14. October–December 2004. http://www.foodcomm.org.uk/17.pdf. Retrieved 8 August 2008.
12. ↑ Barkas, Fotios; Bathrellou, Eirini; Nomikos, Tzortzis; Panagiotakos, Demosthenes; Liberopoulos, Evangelos; Kontogianni, Meropi D. (January 2023). "Plant Sterols and Plant Stanols in Cholesterol Management and Cardiovascular Prevention" (in en). Nutrients 15 (13): 2845. doi:10.3390/nu15132845. ISSN 2072-6643. PMID 37447172.
13. ↑ "Phytosterols as anticancer compounds". Molecular Nutrition & Food Research 51 (2): 161–70. February 2007. doi:10.1002/mnfr.200600164. PMID 17266177.
14. ↑ "A comprehensive classification system for lipids". Journal of Lipid Research 46 (5): 839–61. May 2005. doi:10.1194/jlr.E400004-JLR200. PMID 15722563.
15. ↑ Rodriguez-Estrada, M.T.; Tatay, A. Cilla; Cardenia, V.; Garcia-Llatas, G. (2014), "Fats and Sterols" (in en), Reference Module in Biomedical Sciences (Elsevier), doi:10.1016/B978-0-12-801238-3.00228-2, ISBN 978-0-12-801238-3, https://linkinghub.elsevier.com/retrieve/pii/B9780128012383002282, retrieved 2025-12-22

## Further reading

* "10. Membrane Structure". Molecular biology of the cell. IV. Internal Organization of the Cell. New York: Garland Science. 2002. p. 1874. ISBN 978-0-8153-4072-0. https://www.ncbi.nlm.nih.gov/books/NBK26871/. "The Fluidity of a Lipid Bilayer Depends on Its Composition"

## External links

* Sterols Cyberlipid.org

* v
* t
* e

Structures of the cell membrane

Membrane lipids|

* Lipid bilayer
* Phospholipids
* Lipoproteins
* Sphingolipids
* Sterols

Membrane proteins|

* Membrane glycoproteins
* Integral membrane proteins/transmembrane protein
* Peripheral membrane protein/Lipid-anchored protein

Other|

* Caveolae/Coated pits
* Cell junctions
* Glycocalyx
* Lipid raft/microdomains
* Membrane contact sites
* Membrane nanotubes
* Myelin sheath
* Nodes of Ranvier
* Nuclear envelope
* Phycobilisomes
* Porosomes

* v
* t
* e

Cholestanes, membrane lipids: sterols

* Adosterol
* Cholecalciferol/Ergocalciferols
* Cholesterol
* Dihydrotachysterol
* Fusidic acid
* Lanosterol
* Phytosterols

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