Proteins Involved in Signal Generation

One such type of protein is called an ion channel. These proteins sit across the cell wall with a hydrophobic face exposed to the interior of the wall and hydrophilic ends inside the cell and in the surrounding environment. The central core of the protein takes the form of a tube lined with polar groups which can associate with ions, typically Na+, K+ and Ca2+, and thus allow them to pass through the tube. There is a gate in the tube which can be open or closed and therefore the flow of ions can be turned on or off as required. 

It is likely that at least some of the receptor proteins have sugar units attached to their outer surfaces as they are known to be inactivated by the addition of lectins (proteins which bind to sugars). This fact has been used to demonstrate that the enantiomers of carvone are detected by different receptors since the lectin concanavalin A blocks detection of d-carvone, but not the 1-isomer (Kirner et al., 2003). Conversely, wheat germ agglutinin, another lectin, demonstrates the reverse pattern of blocking (Deutsch and Apfelbach, 2003). 

The portion of the receptor on the inside of the cell is connected to another protein called a G-protein. The key G-protein involved in smell is called transducin, while its counterpart in taste receptor cells is called gustducin. These G-proteins are each actually made up of three different proteins held together as a hetero-trimer. Two other groups of proteins 

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