Growth hormone binds its receptor on hepatocytes and induces transcription of IGF-1 genes. The signal transduction mechanism employed by the growth hormone receptor is:

• A Intrinsic tyrosine kinase activity within the cytoplasmic domain of the receptor
• B Activation of a constitutively associated JAK2 tyrosine kinase ✓
• C Coupling to a G protein that stimulates adenylate cyclase
• D Direct ligand-gated opening of a calcium channel

Explanation

The growth hormone receptor belongs to the class I cytokine receptor superfamily. It has no intrinsic kinase activity; instead, ligand-induced dimerization brings two pre-associated JAK2 molecules together, they transphosphorylate each other, and phosphorylated receptor tyrosines recruit STAT proteins, chiefly STAT5. Option A describes the insulin or EGF receptor family, which have intrinsic tyrosine kinase domains. Option C describes the GPCR family such as the glucagon receptor.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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