Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologymediummcq1 pt

Botulinum toxin enters motor neurons and cleaves their SNARE proteins. Which consequence explains the muscle paralysis that follows?

A.Synaptic vesicles can no longer fuse with the presynaptic membrane, so acetylcholine release stops
B.Acetylcholine receptors on the muscle degrade faster than they are replaced
C.Voltage gated calcium channels close, preventing ion influx during action potentials
D.Neurotransmitter packaging reverses direction and leaks into the neuron

Explanation

Core Concept

SNARE complexes zipper synaptic vesicles into the presynaptic membrane and are required for neurotransmitter discharge. Cleaving them leaves vesicles loaded and calcium signals normal, yet docking and fusion fail, so acetylcholine never reaches muscle receptors and contraction cannot be commanded. The toxin blocks nerve output without damaging the muscle fibers themselves.

Correct Answer

ASynaptic vesicles can no longer fuse with the presynaptic membrane, so acetylcholine release stops

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