Steroidogenesis

The biosynthesis of steroid hormones derives from cholesterol, a molecule with 4 linked rings and 27 carbons. Cholesterol is first converted to a series of progestogens with 21 carbons. Progestogens can be converted by hydroxylation (at carbon 21) to mineralocorticoids or glucocorticoids (both with 21 carbons) or by an elimination reaction to androgens (with 19 carbons). Androgens can in turn be converted to estrogens (with 18 carbons) by the action of an aromatase enzyme that converts ring A to a monocyclic aromatic 6-carbon ring. (Source: Diagram of the pathways of human steroidogenesis. WikiJournal of Medicine 2014. Creative Commons Attribution-Share Alike 3.0 Unported license.)