Whether sniffing flowers, fresh-baked bread or the fumes of a passing automobile, the human olfactory system is an amazing scent sleuth, capable of distinguishing between millions of different smells. Now Weizmann Institute scientists have revealed one of the secrets behind this impressive ability.
In order to produce a response in the olfactory system, molecules of a particular substance must penetrate the nose. There they encounter olfactory receptors -- specialized proteins protruding from the surface of nerve cells in the inner lining of the nose. When an odor molecule lands on a receptor, the nerve cell dispatches an electrical signal to the brain, which processes this information to identify the smell.
Theoretically, one could imagine that for every odor molecule there may be a different receptor, determined by specific genes. However, even if there were, say, only 10,000 discernable smells, this would mean that fully one-tenth of humankind's hereditary code, comprising some 100,000 genes, must be dedicated to smell receptors -- obviously an impossible situation. If, on the other hand, unique receptors do not exist for each individual smell, how does the olfactory system make sense of a vast variety of odors?
Several years ago, Prof. Doron Lancet of the Weizmann Institute's Molecular
Genetics Department proposed that olfactory receptors are
"generalists" which have the capacity to bind with several odor molecules.
Conversely, each odor molecule can bind with a range of potential
receptors. The intensity of the binding varies, depending on the quality of the
fit. Thus, an odor molecule might bind to receptor A with great
intensity, while binding to receptor B with only a mild intensity, and so forth.
The pattern of different bonds creates a unique "fingerprint" that the brain can
understand as a particular smell. The signaling mechanism used by different
receptors is the same, and the brain tells the signals apart by knowing which
nerve cells th
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Contact: Jeffrey J. Sussman
Jeffrey@acwis.org
212-799-2500
American Committee for the Weizmann Institute of Science
29-Jun-1999