The MAP kinase pathway involves a three-tiered kinase cascade. What is the correct sequential order of activation in the Ras-Raf-MEK-ERK pathway?

• A Ras → Raf → MEK → ERK ✓
• B Ras → MEK → Raf → ERK
• C Raf → Ras → MEK → ERK
• D MEK → Raf → Ras → ERK

Explanation

The MAP kinase cascade proceeds as: activated Ras (GTP-bound) recruits Raf (MAPKKK) to the membrane and activates it. Raf phosphorylates and activates MEK (MAPKK), which then phosphorylates and activates ERK (MAPK). ERK translocates to the nucleus to phosphorylate transcription factors. This sequential amplification is fundamental to growth factor signaling.

Reference: Molecular Biology of the Cell, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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