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For a Few Atoms More

When the game becomes less of a game

Roald Hoffmann

Four Atoms Make the World Go 'Round

TestosteroneClick to Enlarge ImageRemarkably enough, the biochemical precursor of testosterone in both sexes is progesterone, a female sex hormone. The difference between progesterone and testosterone is all of four atoms—two carbons and two hydrogens—on the five-membered D ring. Two other female sex hormones, estradiol and estrone, differ from testosterone by the loss of CH3 and an H from the former plus two more hydrogens from the latter. Small changes, indeed, but ones with major consequences.

Other molecular family members with the same 6:6:6:5 fused-ring pattern include ecdysone, the molting hormone of insects; cholesterol, an essential, abundant part of our bodies; cortisones, which are important anti-inflammatory drugs; and bile acids. A pretty incredible set of biological functions, n'est-ce pas? All made distinctive with one less atom here, one more atom there.

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