Correct option is C
G-protein-coupled receptors (GPCRs) are transmembrane receptors that mediate various cellular responses through intracellular effectors. Each ligand/stimulus in Column X operates via specific G-protein signaling pathways, leading to activation of particular effectors in Column Y.
Matching Column X (Ligands/Stimuli) with Column Y (Effectors):
Serotonin → Adenylyl Cyclase (A - iii)
- Serotonin (5-HT) acts through GPCRs (5-HT receptors), primarily associated with Gs proteins, which activate adenylyl cyclase.
- Activation of adenylyl cyclase increases cAMP levels, leading to signal transduction.
Acetylcholine → Potassium Channel/Adenylyl Cyclase (B - iv)
- Acetylcholine (ACh) interacts with muscarinic receptors (M2 in the heart, M3 in smooth muscle).
- M2 muscarinic receptors couple with Gi proteins, which open potassium channels, slowing the heart rate.
- It also inhibits adenylyl cyclase, decreasing cAMP levels.
IgE-antigen complexes → Phospholipase C (C - i)
- IgE-antigen complexes activate FcεRI receptors on mast cells, which trigger Gq protein-mediated signaling.
- Gq proteins activate Phospholipase C (PLC), leading to the production of IP3 and DAG, which increase intracellular Ca²⁺ levels and activate protein kinase C (PKC).
Light → cGMP Phosphodiesterase (D - ii)
- Light activates rhodopsin (a GPCR) in photoreceptors, which couples with transducin (Gt protein).
- Transducin activates cGMP phosphodiesterase, leading to the breakdown of cGMP, causing closure of sodium channels and initiating the phototransduction pathway.
