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Q1 - Conus Snail Toxins and the Neuromuscular Junction

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Nervous System Physiology

Conus snails produce potent conotoxins (peptides), which are used in defense and paralysis of prey. Conotoxins affect the neuromuscular end plates. Four toxins, A-D, have the following effects:

A prevents the inactivation of Na⁺ channels in the presynaptic axon B blocks K⁺ channels in the presynaptic axon C blocks Ca²⁺ channels in the presynaptic end plate D blocks acetylcholine receptors

A, Conus snails; B, model of an unfolded Conus toxin (left) (1-6 are cysteine side chains) and, to the right, one possible 3-D folding through disulphide binding between pairs (e.g. 2 and 5) of cystein (from Safavi-Hermami et al. 2014).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Toxin D inactivates the skeletal muscles
B. Toxins A and B will cause muscle twitching when injected in the prey
C. Toxin C interferes with the exocytosis of neurotransmitters
D. The peptide in Fig. B may be folded in various ways, but all folded molecules have the same effect, if the primary structure of the peptides remains unchanged
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Question reproduced from IBO 2015, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)