Marine toxins: classification, chemistry and pharmacology MCQs With Answer

Introduction: This blog provides a focused set of multiple-choice questions on marine toxins — their classification, chemistry, and pharmacology — tailored for M.Pharm students studying Advanced Pharmacognosy I (MPG 102T). The questions emphasize toxin sources (dinoflagellates, diatoms, cyanobacteria, fish), chemical families (polyether ladder toxins, guanidinium neurotoxins, amino acids), modes of action at molecular targets (voltage-gated ion channels, protein phosphatases, glutamate receptors), clinical syndromes, detection methods and basic management principles. Each MCQ is designed to deepen conceptual understanding and exam preparedness by integrating structural features with pharmacological effects and practical implications relevant to drug research and public health.

Q1. What chemical feature is characteristic of tetrodotoxin responsible for its high affinity to voltage-gated sodium channels?

• Polyether ladder structure
• Guanidinium moiety on a highly oxygenated skeleton
• Sulfonated steroid backbone
• Long-chain polyunsaturated fatty acid

Correct Answer: Guanidinium moiety on a highly oxygenated skeleton

Q2. Paralytic shellfish poisoning (PSP) is primarily caused by which group of toxins?

• Brevetoxins
• Saxitoxins and analogues
• Okadaic acid and dinophysistoxins
• Domoic acid

Correct Answer: Saxitoxins and analogues

Q3. Which marine toxin acts primarily by inhibiting serine/threonine protein phosphatases PP1 and PP2A, causing diarrhetic shellfish poisoning?

• Okadaic acid
• Tetrodotoxin
• Ciguatoxin
• Palytoxin

Correct Answer: Okadaic acid

Q4. Ciguatoxins produce their toxic effects by which primary mechanism at the cellular level?

• Blocking voltage-gated sodium channels from the extracellular side
• Reversibly inhibiting acetylcholinesterase
• Persistently activating voltage-gated sodium channels leading to depolarization
• Antagonizing NMDA receptors

Correct Answer: Persistently activating voltage-gated sodium channels leading to depolarization

Q5. Domoic acid, responsible for amnesic shellfish poisoning, is chemically best described as:

• A polyether marine macrolide
• An amino acid analogue acting as a kainate/AMPA receptor agonist
• A low-molecular-weight guanidinium toxin
• A sulfonated polycyclic ketone

Correct Answer: An amino acid analogue acting as a kainate/AMPA receptor agonist

Q6. Which statement about brevetoxins (produced by Karenia brevis) is TRUE?

• They are hydrophilic guanidinium toxins that block Na+ channels
• They are polyether ladder compounds that activate voltage-gated Na+ channels
• They inhibit protein phosphatases causing gastrointestinal symptoms
• They are excitatory amino acids that bind NMDA receptors

Correct Answer: They are polyether ladder compounds that activate voltage-gated Na+ channels

Q7. Which analytical method is considered the modern standard for identification and quantification of marine toxins in regulatory laboratories?

• Mouse bioassay only
• Thin-layer chromatography
• Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS)
• Colorimetric spot tests

Correct Answer: Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS)

Q8. Palytoxin’s primary pharmacological action is to:

• Inhibit voltage-gated calcium channels
• Convert Na+/K+ ATPase into a non-selective cation channel
• Irreversibly block acetylcholine receptors
• Inhibit mitochondrial electron transport at complex IV

Correct Answer: Convert Na+/K+ ATPase into a non-selective cation channel

Q9. Which marine toxin is classically associated with pufferfish poisoning?

• Saxitoxin
• Tetrodotoxin
• Okadaic acid
• Ciguatoxin

Correct Answer: Tetrodotoxin

Q10. Which property is common to most guanidinium-containing marine neurotoxins (e.g., saxitoxin, tetrodotoxin)?

• They are large lipophilic polyethers
• They selectively block voltage-gated sodium channels at the pore
• They primarily activate glutamate receptors causing excitotoxicity
• They inhibit serine proteases in the gut

Correct Answer: They selectively block voltage-gated sodium channels at the pore

Q11. Which clinical intervention is most critical in severe paralytic shellfish poisoning?

• Immediate chelation therapy
• Respiratory support and mechanical ventilation if required
• High-dose corticosteroids
• Administration of naloxone

Correct Answer: Respiratory support and mechanical ventilation if required

Q12. Anatoxin-a, produced by some cyanobacteria, exerts toxicity primarily by:

• Competitive antagonism of GABA-A receptors
• Irreversible activation of nicotinic acetylcholine receptors causing neuromuscular blockade
• Inhibition of acetylcholinesterase leading to cholinergic crisis
• Direct blockade of L-type calcium channels

Correct Answer: Irreversible activation of nicotinic acetylcholine receptors causing neuromuscular blockade

Q13. Which statement about stability of common marine toxins and food preparation is CORRECT?

• Most marine toxins are heat-labile and destroyed by cooking at 100°C for 10 minutes
• Most marine toxins are heat-stable; conventional cooking often does not inactivate them
• Freezing for 24 hours reliably detoxifies shellfish toxins
• Salting and smoking always eliminate marine toxin risk

Correct Answer: Most marine toxins are heat-stable; conventional cooking often does not inactivate them

Q14. Maitotoxin is notable for which of the following characteristics?

• It is a small guanidinium neurotoxin that blocks Na+ channels
• It is one of the most potent known marine toxins and affects Ca2+ homeostasis
• It inhibits serine proteases in hepatocytes
• It acts as a competitive antagonist at AMPA receptors

Correct Answer: It is one of the most potent known marine toxins and affects Ca2+ homeostasis

Q15. Which toxin class is primarily associated with the “ciguatera fish poisoning” syndrome after consumption of reef fish?

• Cyclic imine toxins (gymnodimines, spirolides)
• Polyether ciguatoxins produced by dinoflagellates
• Hydrophilic guanidinium tetrodotoxins
• Azaspiracids produced by diatoms

Correct Answer: Polyether ciguatoxins produced by dinoflagellates

Q16. Which assay historically used for marine toxin detection measures lethality in live animals but is now being replaced due to ethical and specificity concerns?

• Enzyme-linked immunosorbent assay (ELISA)
• Mouse bioassay
• LC-MS/MS
• Receptor-binding assay with cloned channels

Correct Answer: Mouse bioassay

Q17. Azaspiracid poisoning from contaminated shellfish is primarily characterized by which clinical presentation?

• Severe neuroexcitatory seizures and memory loss
• Predominantly gastrointestinal symptoms such as severe vomiting and diarrhea
• Rapid onset flaccid paralysis and respiratory failure
• Delayed liver failure with jaundice

Correct Answer: Predominantly gastrointestinal symptoms such as severe vomiting and diarrhea

Q18. Which molecular feature distinguishes polyether ladder toxins (e.g., brevetoxins, ciguatoxins) from guanidinium toxins?

• Polyether ladder toxins contain multiple cyclic ether rings forming a ladder-like structure and are lipophilic
• Polyether ladder toxins have a guanidinium group responsible for pore block
• Polyether ladder toxins are hydrophilic amino acid analogues
• Polyether ladder toxins are simple aliphatic hydrocarbons

Correct Answer: Polyether ladder toxins contain multiple cyclic ether rings forming a ladder-like structure and are lipophilic

Q19. A key pharmacological research use of tetrodotoxin and saxitoxin is:

• As irreversible inhibitors of mitochondrial respiration
• As highly selective blockers of voltage-gated sodium channels to study neuronal excitability
• As broad-spectrum antibiotics against marine bacteria
• As activators of protein phosphatases in cancer studies

Correct Answer: As highly selective blockers of voltage-gated sodium channels to study neuronal excitability

Q20. Which management statement regarding marine toxin exposures is MOST accurate?

• There are specific antidotes for most marine toxins widely available in clinical practice
• Management is largely supportive; prevention via monitoring and avoiding contaminated seafood is critical
• Antibiotics are the mainstay of treatment for shellfish toxin poisonings
• Routine dialysis rapidly removes lipophilic marine toxins from blood

Correct Answer: Management is largely supportive; prevention via monitoring and avoiding contaminated seafood is critical

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