Question

Upon binding of a ligand, G-protein-coupled receptors do which of the following?

Select one:

a. The G-protein exchanges a GDP for a GTP, and the alpha subunit detaches from the beta/gamma complex

b. They dimerize, autophosphorylate, and trigger a cascade in intracellular signal transduction/phosphorylation

c. They migrate to the nucleus to activate/repress specific genes

d. They get internalized and start producing cAMP

e. They induce apoptosis

Answer 1

DISCUSSION

G-protein coupled receptors are also called as serpentine receptors and heptahelical receptors. They constitute a large protein family that is responsible for the activation of signal transduction by the detection of extracellular molecules.

They are called seven-transmembrane receptors as it couples with G protein and crosses the cell membrane 7 times. Light sensitive compounds, pheromones, hormones and neurotransmitters are ligands that bind and activate the receptor.

When a ligand binds to GPCR it leads to a conformational change in GPCR. GPCR starts acting like guanine nucleotide exchange factor GEF. The GPCR then activates G protein and exchanges GDP bound to G protein for GTP. The alpha subunit bound to GTP then dissociates from beta and gamma subunit to further affect target protein depending upon the type of alpha unit.

Option A:- Correct

Reason:- The GPCR binds to a ligand and leads to conformational change. The GPCR then activates G protein and exchanges GTP for GDP which triggers the dissociation of alpha subunit from the beta and gamma dimer and receptor.