The sense of taste is essential for the survival of organisms. For example, the ability to identify sweet-tasting foods enables animals to seek out food with high nutritive value, whereas the ability to identify bitter substances enables them to avoid the ingestion of potentially harmful substances. A family of integral membrane proteins are involved in taste perception and include T1R, which is involved in sweet taste perception and T2R, which is involved in bitter taste perception. Both types of taste receptors couple to various G proteins to initiate signal transduction cascades. Specifically, T2R38 is expressed in subsets of taste receptor cells of the tongue and exclusively in gustducin-positive cells. Variations in T2R38 are associated with the ability to taste the bitter chemical phenylthiocarbamide (PTC), also called thiourea tasting.