The MAP kinase (MAPK/ERK) pathway activated by growth factor receptor tyrosine kinases depends on which GTPase as a molecular switch immediately downstream of adaptor proteins Grb2 and SOS?

• A Rho GTPase
• B Ras GTPase ✓
• C Rac GTPase
• D Gsα GTPase

Explanation

Growth factor binding activates receptor tyrosine kinase autophosphorylation → Grb2 (adaptor) binds via its SH2 domain → recruits SOS (guanine nucleotide exchange factor) → SOS catalyzes GDP→GTP exchange on Ras → GTP-Ras is active → activates Raf (MAPKKK) → MEK (MAPKK) → ERK (MAPK) → nuclear translocation → gene transcription (proliferation, differentiation). Mutations in Ras (KRAS, NRAS, HRAS) locking it in GTP-bound active state are among the most common oncogenic mutations in cancer.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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