Shape theory
From Biocrawler, the free encyclopedia.
The Shape theory of smell states that the sensation of smell is due to a 'lock and key' mechanism by which a scent molecule fits into a receptor site in the nose.
The human nose has 347 different receptors, but humans can distinguish thousands of smells. It is possible that there is not a simple one to one relationship between receptors and smells, but instead, that different molecules activate different receptors to different degrees.
Carvone has two isomers, of which one smells like mint and the other like caraway (for which it is named). An experiment reported in Luca Turin's book consisted of mixing the mint isomer with a ketone, on the theory that the shape of the carvone was preventing the ketone receptor from smelling it. The experiment succeeded: a mixture of 60% butanone and 40% mint carvone smells like caraway.
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