Multiple Choice Questions (MCQs)

1. What is necrosis?
○ A) Natural cell death process
○ B) Premature death of cells due to toxic exposure (Correct)
○ C) Overgrowth of cells
○ D) DNA synthesis disruption
2. Which toxin causes necrosis of epithelial cells when ingested or inhaled?
○ A) Ethanol
○ B) Hydrochloric acid (Correct)
○ C) Carbon monoxide
○ D) Dioxins
3. What toxic metabolite is produced in acetaminophen overdose leading to liver
damage?
○ A) NAPQI (Correct)
○ B) Methanol
○ C) Acetylcholine
○ D) Cyanide
4. What is the mechanism of cyanide toxicity?
○ A) Competes with potassium ions
○ B) Binds to hemoglobin
○ C) Inhibits cytochrome c oxidase (Correct)
○ D) Blocks sodium channels
5. Which enzyme does ketoconazole inhibit?
○ A) Acetylcholinesterase
○ B) Cytochrome P450 (Correct)
○ C) Alcohol dehydrogenase
○ D) Dihydrofolate reductase
6. Which toxin mimics potassium and interferes with cellular metabolism?
○ A) Carbon monoxide
○ B) Arsenic
○ C) Thallium (Correct)
○ D) Cyanide
7. Which toxin blocks sodium channels, leading to nerve inhibition?
○ A) Botulinum toxin
○ B) Tetrodotoxin (Correct)
○ C) Cyanide
○ D) Lead
8. What is the effect of organophosphates on enzymes?
 ○ A) Stimulates mitochondrial respiration
○ B) Inhibits acetylcholinesterase (Correct)
○ C) Enhances GABAergic activity
○ D) Stimulates protein synthesis
9. What does carbon monoxide bind to?
○ A) Potassium channels
○ B) Hemoglobin (Correct)
○ C) Ribosomes
○ D) Cytokines
10. Which compound induces liver necrosis and cirrhosis due to chronic use?
○ A) Alcohol (Correct)
○ B) Dieldrin
○ C) Methotrexate
○ D) Corticosteroids
11. What type of inhibition does ketoconazole demonstrate?
○ A) Competitive
○ B) Non-competitive
○ C) Mixed (Correct)
○ D) Irreversible
12. Which substance causes immune suppression and reduces T-cell activation?
○ A) Botulinum toxin
○ B) Ethanol
○ C) Corticosteroids (Correct)
○ D) Lead
13. What substance disrupts mitochondrial protein synthesis?
○ A) Chloramphenicol (Correct)
○ B) Methotrexate
○ C) Carbon monoxide
○ D) Organophosphates
14. What is the target of methotrexate toxicity?
○ A) DNA synthesis (Correct)
○ B) Sodium channels
○ C) Cytochrome oxidase
○ D) Hemoglobin
15. Which substance blocks acetylcholine release, leading to paralysis?
○ A) Botulinum toxin (Correct)
○ B) Organophosphates
○ C) Cyanide
○ D) Amphetamines
16. Which of the following toxins leads to overstimulation of the nervous system?
 ○ A) Lead
○ B) Amphetamines (Correct)
○ C) Arsenic
○ D) Dioxins
17. How does ethanol reduce methanol toxicity?
○ A) Enhances immune response
○ B) Competes for alcohol dehydrogenase (Correct)
○ C) Stimulates neurotransmitter release
○ D) Reduces cytochrome c activity
18. What enzyme does organophosphate inhibit?
○ A) Alcohol dehydrogenase
○ B) Acetylcholinesterase (Correct)
○ C) Dihydrofolate reductase
○ D) Hemoglobin
19. Which toxin causes autoimmune hemolytic anemia?
○ A) Dioxins
○ B) Pesticides (Correct)
○ C) Alcohol
○ D) Carbon monoxide
20. Which of the following causes immune suppression?
○ A) Lead
○ B) Corticosteroids (Correct)
○ C) Thallium
○ D) Cyanide
21. Which mechanism is linked to halting aerobic cell metabolism?
○ A) Arsenic
○ B) Thallium
○ C) Cyanide (Correct)
○ D) Ethanol
22. How do dioxins affect the immune system?
○ A) Enhance antibody production
○ B) Suppress cellular and humoral immunity (Correct)
○ C) Stimulate cytokine production
○ D) Increase macrophage activity
23. Which toxin damages the respiratory tract due to epithelial necrosis?
○ A) Hydrofluoric acid (Correct)
○ B) Arsenic
○ C) Carbon monoxide
○ D) Methotrexate
24. What is a functional effect of lead toxicity on the nervous system?
 ○ A) Paralysis
○ B) Cognitive deficits (Correct)
○ C) Hemolytic anemia
○ D) Paralysis of muscles
25. Which compound mimics neurotransmitters and overstimulates nerves?
○ A) Lead
○ B) Amphetamines (Correct)
○ C) Cyanide
○ D) Methotrexate
26. Which toxicant causes oxidative phosphorylation disruption?
○ A) Thallium
○ B) Arsenic (Correct)
○ C) Ethanol
○ D) Lead
27. Which compound directly binds to ribosomes to inhibit protein synthesis?
○ A) Chloramphenicol (Correct)
○ B) Methotrexate
○ C) Botulinum toxin
○ D) Cyanide
28. Which immune-suppressive toxin reduces NK cell activity?
○ A) Alcohol (Correct)
○ B) Arsenic
○ C) Thallium
○ D) Cyanide
29. Which of these is produced by Aspergillus fungi and causes hepatic necrosis?
○ A) Dioxins
○ B) Aflatoxins (Correct)
○ C) Ethanol
○ D) Hydrofluoric acid
30. What is the primary target of cyanide poisoning?
○ A) Ribosomes
○ B) Mitochondrial cytochrome oxidase (Correct)
○ C) Potassium transporters
○ D) Hemoglobin

Answers to Open Questions

1. Define necrosis and give two examples of toxicants causing epithelial necrosis.
Answer: Necrosis is the premature death of cells and living tissue, often caused by direct
damage or exposure to toxic substances. Examples:
 ○ Hydrochloric acid (HCl): Causes necrosis when inhaled or ingested due to direct
epithelial damage.
○ Aflatoxins: Produced by Aspergillus fungi, leading to hepatic necrosis and liver
damage.
2. Describe how ketoconazole affects cytochrome P450 enzymes.
Answer: Ketoconazole inhibits cytochrome P450 enzymes (CYP3A) by binding to both
the active site and allosteric sites. This mixed inhibition reduces enzyme activity and
disrupts the metabolism of drugs and xenobiotics, potentially leading to toxicity.
3. Explain how alcohol can act as both a toxicant and a competitive inhibitor in
enzyme activity.
Answer:
○ As a toxicant, alcohol (ethanol) causes cellular dehydration, lipid peroxidation,
and necrosis, especially in the liver, leading to cirrhosis or hepatitis.
○ As a competitive inhibitor, ethanol competes with methanol for alcohol
dehydrogenase. This prevents methanol metabolism into its toxic metabolites, like
formaldehyde, mitigating methanol toxicity.
4. What are the effects of botulinum toxin on nerve function?
Answer: Botulinum toxin blocks acetylcholine release at neuromuscular junctions by
inhibiting vesicle fusion. This leads to muscle paralysis, as nerve signals cannot trigger
muscle contractions.
5. Discuss the mechanism of organophosphate toxicity in the nervous system.
Answer: Organophosphates inhibit acetylcholinesterase, the enzyme that breaks down
acetylcholine in nerve synapses. This results in excessive accumulation of acetylcholine,
leading to overstimulation of nerves, muscle twitching, and paralysis.
6. What role does cyanide play in halting cellular respiration?
Answer: Cyanide binds to cytochrome c oxidase in the mitochondrial electron transport
chain. This blocks the reduction of oxygen to water, halting aerobic respiration and
causing cellular hypoxia.
7. Describe the immune effects of dioxins on cellular and humoral immunity.
Answer: Dioxins suppress both cellular and humoral immunity. They reduce immune
cell proliferation, decrease antibody production, and impair the function of critical
immune responses, making the body susceptible to infections.
8. How does thallium mimic potassium in cellular processes?
Answer: Thallium mimics potassium by using potassium transport systems to enter cells.
This interference disrupts normal potassium ion transport, leading to impaired cellular
metabolism and neurological dysfunction.
9. List two toxicants that interfere with DNA synthesis and their mechanisms.
Answer:
○ Methotrexate: Inhibits dihydrofolate reductase, preventing DNA synthesis and
cell replication.
 ○ Chloramphenicol: Inhibits mitochondrial protein synthesis by binding to
ribosomes, indirectly disrupting DNA synthesis.
10. What are the consequences of lead accumulation in the nervous system?
Answer: Lead accumulates in the brain and interferes with neurotransmitter release,
resulting in cognitive deficits, developmental delays, neuropathy, and impaired learning
and memory functions.

Answers to Essay Questions

1. Discuss the mechanisms of intoxication leading to necrosis, providing detailed

examples of toxicants and their effects.
Answer: Necrosis refers to the premature death of cells due to toxic exposure, physical
injury, or other factors that disrupt membrane integrity and cell function.
○ Hydrochloric acid (HCl): Causes immediate epithelial necrosis when inhaled or
ingested due to its corrosive nature, leading to tissue inflammation and cell death.
○ Alcohol (ethanol): Chronic exposure leads to lipid peroxidation and dehydration
of cells, causing liver necrosis and conditions like alcoholic hepatitis or cirrhosis.
○ Aflatoxins: Produced by fungi (Aspergillus species), these toxins cause hepatic
necrosis and liver damage when ingested through contaminated food.
○ Mustard Gas: Leads to severe necrosis in the respiratory tract and skin due to its
cytotoxic effects.
In conclusion, necrosis caused by toxicants is a serious health concern,
particularly in epithelial tissues, as it can lead to organ failure and systemic
damage.
2. Explain how competitive and non-competitive enzyme inhibition occur, giving
examples of toxins for each mechanism.
Answer: Enzyme inhibition occurs when substances interfere with enzyme activity,
impairing normal metabolic processes.
○ Competitive inhibition: The toxicant competes with the substrate for the
enzyme's active site, preventing the substrate from binding.
Example: Ethanol competes with methanol for alcohol dehydrogenase, preventing
the conversion of methanol into toxic formaldehyde.
○ Non-competitive inhibition: The toxicant binds to an allosteric site (not the
active site), altering the enzyme's shape and reducing its activity.
Example: Cyanide binds to cytochrome c oxidase in the mitochondrial electron
transport chain, stopping cellular respiration.
Both types of inhibition can severely disrupt cellular function, leading to toxicity
and organ damage.
3. Describe the role of cyanide and carbon monoxide in interfering with body
metabolism, including their effects on cellular respiration.
 Answer: Cyanide and carbon monoxide are potent metabolic disruptors that interfere
with oxygen delivery and utilization.
○ Cyanide: Binds to cytochrome c oxidase in mitochondria, halting the electron
transport chain and blocking aerobic respiration. This prevents cells from
producing ATP, leading to energy failure and cell death.
○ Carbon monoxide (CO): Binds to hemoglobin with a higher affinity than oxygen,
forming carboxyhemoglobin. This reduces oxygen transport in the blood and
causes systemic hypoxia.
Both toxins lead to cellular energy depletion, organ dysfunction, and death if
exposure is prolonged.
4. Analyze the functional effects of toxicants on the nervous system, discussing the
mechanisms of action of lead, amphetamines, and tetrodotoxin.
Answer: Toxicants can mimic, block, or interfere with neurotransmitter functions,
leading to nervous system disruption.
○ Lead: Accumulates in the brain, interfering with neurotransmitter release and
causing cognitive deficits, developmental delays, and neuropathy.
○ Amphetamines: Overstimulate the nervous system by increasing dopamine and
norepinephrine release. While they enhance alertness, excessive stimulation
causes anxiety, paranoia, and cardiovascular issues.
○ Tetrodotoxin (TTX): Blocks sodium channels in nerves and muscles, preventing
action potential generation and leading to paralysis.
These toxicants demonstrate the diverse ways the nervous system can be
disrupted, causing severe functional impairments.
5. Evaluate the impact of immunosuppressive agents on the human immune system,
with examples of therapeutic and toxic substances.
Answer: Immunosuppressive agents reduce immune response, making individuals
vulnerable to infections and diseases.
○ Corticosteroids (e.g., prednisone): Used therapeutically to manage inflammation,
they suppress T-cell activation and cytokine production but can cause toxicity in
high doses.
○ Alcohol: Chronic alcohol consumption impairs macrophage function and reduces
NK cell activity, weakening immune defenses.
○ Polychlorinated Biphenyls (PCBs): Suppress immune cell proliferation and
antibody production, increasing infection susceptibility.
○ Dioxins (TCDD): Reduce both cellular and humoral immune responses,
compromising overall immunity.
While some immunosuppressants are used medically to treat autoimmune
conditions, their toxic effects highlight the need for controlled use to prevent
harmful immunodeficiency.