Sterol
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Sterols, or steroid alcohols are a subgroup of steroids with a hydroxyl group in the 3-position of the A-ring. They are amphipathic lipids synthetised from acetyl-coenzyme A. The overall molecule is quite flat. The hydroxyl group on the A ring is polar. The rest of the aliphatic chain is non-polar.
Sterols are important for the physiology of eukaryotic organisms. They form part of the cellular membrane where they modulate their fluidity and function and participate as secondary messengers in developmental signaling.
Different organisms use different sterols. The most important ones are cholesterol, phytosterols, and some steroid hormones in animals, and campesterol, sitosterol and stigmasterol in plants.
Sterols are also known to block cholesterol absorption sites in the human gut thus helping to reduce cholesterol in humans by up to 15%.
Sterols of plants are called phytosterols; and sterols of animals are called zoosterols.
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