Matching Receptor Tyrosine Kinase, cGMP, GAP, and Nuclear Receptors Explained

Receptor tyrosine kinase matches with insulin signal reception, while GTPase activating protein inactivates G-proteins. The correct option is (D) P-2, Q-4, R-1, S-3.
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Correct Matching

• P (Receptor tyrosine kinase) → 2 (Reception of insulin signal): Insulin receptor functions as a receptor tyrosine kinase (RTK), autophosphorylating upon ligand binding to propagate signals via the PI3K-Akt pathway.
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• Q (Cyclic GMP or cGMP) → 4 (Receptor guanylyl cyclase): Receptor guanylyl cyclases produce cGMP as a second messenger, notably in processes like phototransduction in rod cells.
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• R (GTPase activating protein or GAP) → 1 (Inactivation of G-proteins): GAPs accelerate GTP hydrolysis on Gα subunits, rapidly switching off heterotrimeric G-protein signaling.
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• S (Nuclear receptor) → 3 (Thyroid hormone): Thyroid hormones (T3, T4) bind nuclear receptors like TRα and TRβ, modulating gene transcription as ligand-activated transcription factors.
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Why Other Options Fail

Option (A) P-1, Q-3, R-4, S-2 mispairs RTK with G-protein inactivation (RTKs act independently) and cGMP with thyroid hormone (unrelated pathways).
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Option (B) P-2, Q-4, R-3, S-1 incorrectly links GAP to thyroid hormone (thyroid uses nuclear receptors) and nuclear receptors to G-protein inactivation.
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Option (C) P-3, Q-1, R-4, S-2 wrongly assigns RTK to thyroid hormone (thyroid receptors are nuclear) and cGMP to G-protein inactivation.
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