Steroids and Sterols
Steroids have two principal biological functions - as important components of cell membranes which alter membrane fluidity and as signaling molecules. Hundreds of steroids are found in plants, animals and fungi. All steroids are produced in cells from the sterols lanosterol (animals and fungi) or cycloartenol (plants). Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, and can be also produced by some bacteria. The most well-known type of animal sterol is cholesterol, which is vital to cell membrane structure, and functions as a precursor to fat-soluble vitamins and steroid hormones.