Before You Begin
Question #46787
The Question
A researcher applies a novel neurotoxin to a chemical synapse. The toxin does not competitively bind to post-synaptic receptors, nor does it affect pre-synaptic voltage-gated calcium channels. Instead, it permanently alters the resting membrane potential of the post-synaptic membrane, drastically shifting its local electrostatic environment. Despite normal exocytosis of the neurotransmitter, synaptic transmission completely fails. Which of the following best explains this failure at the molecular level?
Options
- A.
The altered electrostatic environment disrupts the tertiary structure of the post-synaptic receptors, abolishing their ligand-binding affinity.
- B.
The neurotoxin prevents the influx of calcium ions into the post-synaptic neuron, halting the generation of an excitatory post-synaptic potential.
- C.
The altered post-synaptic membrane potential directly hyperactivates neurotransmitter-degrading enzymes in the synaptic cleft.
- D.
The pre-synaptic vesicles fail to undergo exocytosis because the post-synaptic depolarization inhibits retrograde chemical signaling.
Check Your Answer
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
Neurotransmitter Receptor Specificity|Resting Membrane Potential Ionic Flux|Peptide Bond Geometry
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating 'Biomolecules' (protein conformation) with 'Neural Control' (synaptic transmission).
Students typically memorize that receptor binding causes a change in membrane potential, but fail to recognize the reverse dependency: the resting membrane potential provides the electrostatic environment required to maintain the receptor's functional tertiary structure.
The trap in Option B exploits the common location-based confusion regarding where calcium ion influx is strictly required (pre-synaptic vs. post-synaptic).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biomolecules - Class 11 |
| Concept | Peptide Bond Geometry |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |