Question

For each of the following sentences, select the best word or phrase from the list below to fill in the blanks. Not all words or phrases will be used; each word or phrase should be used only once.

G-protein-coupled receptors (GPCRs) all have a similar structure with _____ transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of three subunits, becomes activated. _______ of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to ______, which is exchanged for _____ on stimulation. The intrinsic GTPase activity of the α subunit is important for inactivating the G protein. _________ inhibits this activity of the α subunit, thereby keeping the subunit in an active state.

Options:
a) seven, three, four, GDP, GTP, GTPase
b) four, three, seven, GDP, GTP, GTPase
c) seven, four, three, GTP, GDP, GTPase
d) three, seven, four, GTP, GDP, GTPase

Answer 1

G-protein-coupled receptors (GPCRs) have seven transmembrane domains and three tethered subunits. The α subunit is bound to GDP, which is exchanged for GTP upon stimulation. GTPase inhibits the intrinsic GTPase activity of the α subunit.

Step-by-step explanation:

G-protein-coupled receptors (GPCRs) all have a similar structure with seven transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of three subunits, becomes activated.

Three of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to GDP, which is exchanged for GTP on stimulation.

The intrinsic GTPase activity of the α subunit is important for inactivating the G protein. GTPase inhibits this activity of the α subunit, thereby keeping the subunit in an active state.