Mammalian Taste Receptor Gene Family

Aside from the main olfactory system, mammals
have evolved two other chemosensory
systems, the taste receptor gene family (for bitter
taste) and the mammalian pheromone receptor
gene family. Five different types of taste
can be perceived: salty, sour, bitter, sweet, and
umani (the taste of monosodium glutamate,
present in Asian food). Salty and sour tastes involve
direct effects due to the entry of H+ and
Na+ ions through specialized membrane channels.
In contrast, bitter, sweet, and umani tastes
are mediated via a G protein-coupled receptor
(GPCR) signaling pathway system. A sweet taste
may herald a desirable carbohydrate content,
whereas a bitter taste is associated with potentially
toxic substances such as alkaloids, cyanides,
or other detrimental aromatic compounds.