Categories: Economic botany and plant uses; medicine and health
While the female hormones called estrogens are common in mammals, only a few plants contain estrogens. Others synthesize compounds which are chemically unrelated to estrogens but resemble them in their molecular size and shape. These compounds are called phytoestrogens (plant estrogens) and may, when ingested by animals or humans, have properties similar to those of mammalian estrogens.
The precursor of estrogens in plants and animals as squalene. Cyclization of squalene, via the inter-is the linear (straight-chain) triterpene known mediate cycloartenol in plants and via the interme-
diate lanosterol in animals, forms a group of very important compounds known as the steroids. Steroids include cholesterol, mammalian sex hormones (including the estrogens and androgens), corticosteroids, insects' molting hormones, and plant brassinosteroid hormones. All steroids have a tetracyclic (four-ringed) structure; the rings are named A, B, C, and D. Differences in the functional groups attached to the tetracyclic skeleton, differences in the side-chain attached to ring D, and differences in the overall shape of the molecule determine a steroid's biological activity.
Estrogens have an aromatic A ring (a ring of six carbon atoms joined by alternating single and double bonds). This constrains the junction between the A and B rings, resulting in a "flat," or planar, molecule. This shape is essential for the potent biological activity of estrogens, and chemical modifications that alter the planar nature of an estrogen molecule reduce its biological activity.
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