Olfaction, Chemical Biology of

Abstract

Smell is an intriguing sense in many ways. Although it is not the dominant sense in humans, it has affects on emotion and memory which can be very profound. Odor has long baffled chemists who try to model it in mechanistic terms, and a great deal of research has been invested in trying to understand how various features of molecular structure provide different odor characters and intensities. Many models for prediction of odor properties from chemical structure exist, but none are accurate and precise consistently. The reasons for this are now becoming clearer. The greatest breakthroughs in our understanding of olfaction came with the discoveries of the gene family coding for the olfactory receptor proteins (1) and the combinatorial mode of operation of these receptors (2). Odorous molecules enter the nose either from the front, by inhalation, or from the back, by diffusion from the mouth and respiratory tract. In the nose, they interact with an array of receptors. Each receptor type responds to a range of odorants, and each odorant stimulates a range of receptors. The signals thus generated are coded onto centers, known as glomeruli, in the olfactory bulb. The olfactory signals pass on upward through the brain and are interpreted finally, in the cortex, as odor. During the neurotransmission process, many interactions occur between olfactory signals and cortical feedback mechanisms, which include effects from other senses. Therefore, it is not surprising that simple structure/odor correlations are so elusive.