Sweet taste receptors are activated when which molecules bind to what type of receptors?

• A. Sugar molecules binding to ion channels
• B. Sugar molecules binding to G-protein coupled receptors
• C. Sugar molecules binding to tyrosine kinases
• D. Sugar molecules crossing the membrane freely

Answer: (B)

Sweet taste detection relies on a G-protein–coupled receptor on taste receptor cells. When a sugar or sweetener binds, it activates a heterodimeric receptor (T1R2/T1R3) that couples to a G protein such as gustducin. This sets off a signaling cascade with phospholipase Cβ2, production of IP3, release of Ca2+ from internal stores, and opening of the TRPM5 channel. The cell then depolarizes and releases ATP to the gustatory nerves, giving the sensation of sweetness. So sugars bind to a GPCR, not to an ion channel, a tyrosine kinase, or by crossing the membrane freely.