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Question #45448
The Question
In a pathological condition, a target cell exhibits continuous, unregulated metabolic responses normally controlled by a protein hormone, even in the complete absence of the hormone. Biochemical analysis reveals persistently high intracellular levels of the secondary messenger, cyclic AMP (cAMP). Which of the following molecular defects in the membrane-bound receptor complex best explains this phenomenon?
Options
- A.
Loss of intrinsic GTPase activity in the G-protein, preventing the hydrolysis of GTP to GDP.
- B.
A structural mutation that permanently locks the G-protein in a GDP-bound state.
- C.
Constitutive upregulation of intracellular phosphodiesterase enzyme activity.
- D.
Inability of the membrane-bound receptor to undergo a conformational change upon ligand binding.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Adenylate_Cyclase|Protein_Kinase_A|Hormone_Receptors_Location
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that G-proteins require GTP but fail to distinguish the active vs. inactive states.
The trap lies in understanding that intrinsic GTPase activity is responsible for signal termination, not initiation.
Losing this 'off switch' leads to constitutive activation, a classic oncogenic or syndromic mechanism (e.g., McCune-Albright syndrome).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Chemical Coordination and Integration - Class 11 |
| Concept | Secondary Messenger Cascade |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |