Olfaction Theory

A short history of olfaction theories

1. Molecular shape (“lock and key” model)

Generally, odorants activate many olfactory receptors, as the receptors are more about the properties of the substance than the substance itself. A particular odorant will bond only to the receptors it corresponds to, enabling a person to identify the smell. Odorants and receptors can be imagined as a lock and key pair.

SIGNAL TRANSDUCTION

Action potentials (electrical signals) convey information along neurons. Electrical changes in receptor cells initiate these signals. Chemicals induce these signals in chemoreceptors. Ion channels are openings in the cell membrane that allow the movement of ions through them. Positively charged ions like sodium ions move into

The form of the pocket depends greatly on the sequence of amino acids forming the protein. Thus, the sequence of amino acids that make the protein is crucial. A single change in the order can change the shape of the pocket leading to changes in the chemicals that fit into the pocket. An example to support this argument can be an olfactory receptor protein in rats that responds greatly on interaction with octanol (an alcohol with eight carbon atoms) as compared to its interaction with heptanol (an alcohol with seven carbons). One amino acid that is believed to affect the shape of the pocket is valine, which is present in the fifth transmembrane domain. Changing it to isoleucine alters the shape of the pocket in such a way that the maximum effect is generated by heptanol instead of octanol. The importance in determining the specificity of receptor cells of the amino acid molecules is highlighted in this

The vibrational energy of the molecule will have increased by E after tunnelling. To reiterate, only when the difference in energy levels of the donor and acceptor is equal to the molecular vibrationsal energy, E, tunnelling occurs. Thus, the receptor detects a single well-defined energy, E, making it operate as a spectrometer. Only a molecule with the right vibrational energy present in the gap causes a tunnelling current to flow across the device, a prerequisite being the change in energy between the donor and acceptor levels being sufficiently large. The relative strengths of the coupling affects which state(s) will get excited if there are many vibrational modes. This may be expected to depend on the relative orientation of charge movements with respect to the electron tunnelling path and the particle charges along with several other