Growth hormone binds its receptor on a hepatocyte. The signal transduction mechanism used by the growth hormone receptor is:

• A Intrinsic tyrosine kinase activity leading to IRS-1 phosphorylation
• B JAK2 recruitment followed by STAT5 phosphorylation and dimerization ✓
• C Gs-alpha activation leading to increased intracellular cAMP
• D Ligand-gated ion channel opening at the plasma membrane

Explanation

The growth hormone receptor lacks intrinsic kinase activity. Ligand binding induces receptor dimerization, bringing two associated JAK2 tyrosine kinases together for trans-phosphorylation. Phosphorylated receptor residues recruit STAT5, which is itself phosphorylated, dimerizes, and enters the nucleus to drive transcription of genes such as IGF-1. Option A describes the insulin receptor family, which has intrinsic tyrosine kinase domains, whereas the GH receptor belongs to the class I cytokine receptor superfamily that depends on Janus kinases.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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