Cell Signalling and Receptor Mechanisms · USMLE Step 1

If a mutation prevented GTP hydrolysis by a Gα subunit in a GPCR pathway, what would be the most likely result?

  1. Complete failure to activate any downstream effector molecules
  2. Prolonged, sustained activation of downstream signaling
  3. Immediate internalization and degradation of the receptor
  4. No measurable effect on the duration of signaling
Show answer and explanation

Correct answer: Prolonged, sustained activation of downstream signaling

Without GTP hydrolysis, the Gα subunit remains in its active GTP-bound state, continuously stimulating downstream effectors and prolonging the signal.

Difficulty: Medium Question 16 of 22

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