Insulin binding to its receptor initiates signal transduction in target cells. Which statement correctly describes the insulin receptor and its immediate post-receptor events?

• A It is a Gs-coupled receptor that activates adenylyl cyclase and protein kinase A
• B It has intrinsic tyrosine kinase activity and phosphorylates IRS proteins on tyrosine residues ✓
• C It is linked to JAK-STAT signaling via growth hormone receptor homodimers
• D It has intrinsic serine/threonine kinase activity and directly phosphorylates GLUT4

Explanation

The insulin receptor is a heterotetramer with intrinsic tyrosine kinase activity in its beta subunits. Ligand binding causes autophosphorylation, followed by tyrosine phosphorylation of insulin receptor substrate (IRS) proteins, which recruit PI3-kinase and drive GLUT4 translocation in muscle and fat. Option A describes glucagon-like GPCR signaling, and option C describes the growth hormone pathway, making both categorically wrong for insulin.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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