Final answer:
Sweet and umami tastants bind to G protein receptors on taste hairs. Sweet receptors are activated by sugars and sweeteners, while umami receptors respond to the amino acid L-glutamate, commonly found in protein-rich foods.
Step-by-step explanation:
The tastants that bind to G protein receptors on taste hairs are sweet and umami. These receptors are responsible for the transduction of the sweet, bitter, and umami tastes. They function by binding with their specific tastants, which in turn activates a G protein signal transduction system leading to the depolarization of the gustatory cell.
The sweet taste is most commonly associated with the presence of sugars such as glucose and fructose in the saliva, which activates the sweet receptors. Artificial sweeteners like aspartame and sucralose also trigger these receptors. The umami taste, which is considered savory, is activated by the amino acid L-glutamate and is typically detected in protein-rich foods. Both sweet and umami tastants require a G-protein coupled receptor to excite the specialized neurons associated with them, differentiating them from tastes like salty and sour which are directly triggered by specific ions.