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Chemical Reaction: Nose News
By: Steve Herman
Posted: January 8, 2007, from the January 2007 issue of GCI Magazine.
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There are two glumerili for each receptor family, one on each side of the nose. Thus each rose receptor (not a real type of receptor), expressed on thousands olfactory cilia, connect to one of two rose glumerili, and so on for each of the 347 different functioning genes. The mechanism is clearly combinatorial, since humans can smell far more than 347 different odors.
Chemoreception, the ways chemicals around you are sensed, consists of the olfactory system, the trigeminal nerve and the Volmeronasal Organ (VNO) or Jacobson’s Organ. The trigeminal nerve is a hazardous warning system spread around the face, which may have some odor perception capability. The VNO is the putative human pheromone receptor. The existence and importance of human pheromones has been a controversial area of chemoreception science.
Insect pheromones are well-known, in addition to some animal pheromones. Pheromones have a variety of purposes, such as marking territory or laying down a path to food. Androstenone is called a pig pheromone by its detractors, to shed a bad light on its human effects. The classic work establishing the existence of human pheromones is McClintock’s work on menstrual synchrony.2 Note that McClintock refers to pheromones defined as chemical signals, not sexual attractants.
Buck’s recent work3 discloses a new family of chemoreceptors. The new class, trace amine-associated receptors or TAARs, are present in humans, mice and fish. The work done on mice showed recognition of volatile amines found in three sources: urine, a compound linked to stress and a potential pheromone. The ligands identified are thus associated with social cues rather than odorants. Extension of this work into humans can potentially yield a previously unknown mechanism for pheromone response.
Biology students have a simple experiment to show the effects of genetics in taste perception. It involves individual differences in the ability to detect phenylthiocarbamide (PTC) and propylthiouracil (PROP), materials with a bitter taste. It is absolutely hereditary. Globally, 55% of all humans can taste it and 45% cannot. The gene has been precisely identified4 and involves a G-protein that responds to the N – C = S moiety.