In plants and animals, steroids appear to be biosynthesized by similar reactions, beginning with acetic acid, assisted by a type of enzyme. The isoprenoid hydrocarbon called squalene, which occurs widely in nature, is thought to be the starting material from which all steroids are made. Enzymatic transformation of squalene produces lanosterol in animals and cycloartenol in plants, which yield cholesterol in both animals and plants. Cholesterol is then converted to bile acids and steroid hormones in animals and to steroids such as alkaloids in plants. Steroids are probably synthesized in all vertebrates and in many invertebrates by the same pathway, ...(100 of 7003 words)