Enzyme inhibition MCQs With Answer

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Introduction: Enzyme inhibition MCQs With Answer is a focused resource designed for B. Pharm students to strengthen understanding of mechanisms, kinetics, and clinical implications of enzyme inhibitors. This set covers reversible and irreversible inhibition, competitive, noncompetitive, uncompetitive and mixed inhibition, Ki interpretation, Michaelis–Menten and Lineweaver–Burk analyses, mechanism-based (suicide) inhibitors, allosteric modulation, and drug–drug interactions. Questions emphasize calculation, graph interpretation, laboratory assays, and therapeutic examples such as ACE inhibitors, MAO inhibitors, and acetylcholinesterase inhibitors. Clear explanations encourage application to pharmacokinetics, pharmacodynamics, and drug design. Practice with these MCQs will build confidence for exams and practicals. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which type of enzyme inhibition increases apparent Km without changing Vmax?

  • Competitive inhibition
  • Noncompetitive inhibition
  • Uncompetitive inhibition
  • Irreversible inhibition

Correct Answer: Competitive inhibition

Q2. Which inhibition is characterized by a decrease in Vmax with no change in Km (pure form)?

  • Competitive inhibition
  • Noncompetitive inhibition
  • Uncompetitive inhibition
  • Mixed inhibition

Correct Answer: Noncompetitive inhibition

Q3. Uncompetitive inhibitors bind preferentially to which form of the enzyme?

  • Free enzyme (E)
  • Enzyme-substrate complex (ES)
  • Allosteric inactive enzyme (Ei)
  • Covalently modified enzyme

Correct Answer: Enzyme-substrate complex (ES)

Q4. Which plot type is commonly used to linearize Michaelis–Menten data and visualize inhibition effects?

  • Lineweaver–Burk plot (double reciprocal)
  • Michaelis plot (v vs [S])
  • Scatchard plot
  • Henderson–Hasselbalch plot

Correct Answer: Lineweaver–Burk plot (double reciprocal)

Q5. In a Lineweaver–Burk plot, competitive inhibition lines intersect at which point?

  • Same x-intercept, different y-intercepts
  • Same y-intercept, different x-intercepts
  • Parallel lines
  • Coincident lines

Correct Answer: Same y-intercept, different x-intercepts

Q6. A lower Ki value indicates what about an inhibitor?

  • Weaker binding affinity
  • Stronger binding affinity
  • No effect on enzyme activity
  • Irreversible binding only

Correct Answer: Stronger binding affinity

Q7. Which example represents a mechanism-based (suicide) inhibitor used in pharmacology?

  • Captopril (ACE inhibitor)
  • Clavulanic acid (beta-lactamase inhibitor)
  • Organophosphate nerve agents
  • 5-Fluorouracil (mechanism-based inhibitor of thymidylate synthase)

Correct Answer: 5-Fluorouracil (mechanism-based inhibitor of thymidylate synthase)

Q8. Which laboratory observation suggests irreversible inhibition?

  • Activity recovers after dialysis
  • Activity recovers after dilution
  • Activity does not recover after removal of inhibitor
  • Lineweaver–Burk lines intersect at y-axis

Correct Answer: Activity does not recover after removal of inhibitor

Q9. Mixed inhibition affects which kinetic parameters?

  • Only Km
  • Only Vmax
  • Both Km and Vmax
  • Neither Km nor Vmax

Correct Answer: Both Km and Vmax

Q10. Which clinical drug class is a classic example of competitive enzyme inhibitors?

  • ACE inhibitors like captopril
  • Organophosphate insecticides
  • Monoamine oxidase irreversible inhibitors
  • Sulfonylureas

Correct Answer: ACE inhibitors like captopril

Q11. In an uncompetitive inhibition scenario, how are Km and Vmax affected?

  • Km increases, Vmax unchanged
  • Km unchanged, Vmax decreases
  • Both Km and Vmax decrease
  • Both Km and Vmax increase

Correct Answer: Both Km and Vmax decrease

Q12. Which inhibitor type can be overcome by increasing substrate concentration?

  • Noncompetitive inhibitor
  • Uncompetitive inhibitor
  • Competitive inhibitor
  • Irreversible inhibitor

Correct Answer: Competitive inhibitor

Q13. Organophosphates inhibit acetylcholinesterase primarily by which mechanism?

  • Competitive reversible inhibition
  • Allosteric activation
  • Irreversible phosphorylation of active site serine
  • Uncompetitive inhibition of ES complex

Correct Answer: Irreversible phosphorylation of active site serine

Q14. On a Dixon plot (1/v vs [I]), the intersection point of lines from different [S] gives an estimate of what?

  • Vmax
  • Km
  • Ki
  • IC50 only

Correct Answer: Ki

Q15. Heavy metals like mercury often inhibit enzymes by binding to which amino acid residue?

  • Glycine
  • Serine
  • Cysteine (sulfhydryl groups)
  • Proline

Correct Answer: Cysteine (sulfhydryl groups)

Q16. Which statement about IC50 is true?

  • IC50 is independent of substrate concentration
  • IC50 depends on assay conditions including [S]
  • IC50 equals Ki for all inhibitors
  • IC50 measures irreversible binding only

Correct Answer: IC50 depends on assay conditions including [S]

Q17. A competitive inhibitor will change the slope of Lineweaver–Burk plot how?

  • Slope decreases
  • Slope increases
  • Slope unchanged
  • Lines become parallel

Correct Answer: Slope increases

Q18. Which technique helps distinguish reversible from irreversible inhibition in vitro?

  • Measuring Km only
  • Dialysis or dilution to remove inhibitor
  • Colorimetric substrate alone
  • Only Lineweaver–Burk plot

Correct Answer: Dialysis or dilution to remove inhibitor

Q19. In mixed inhibition where inhibitor prefers free enzyme, how is apparent Km affected?

  • Apparent Km decreases
  • Apparent Km increases
  • Apparent Km unchanged
  • Apparent Km becomes zero

Correct Answer: Apparent Km increases

Q20. Which pharmacological inhibitor type often forms a covalent bond with the enzyme?

  • Reversible competitive inhibitors
  • Irreversible inhibitors
  • Allosteric reversible modulators
  • Substrate analogs that are nonreactive

Correct Answer: Irreversible inhibitors

Q21. Which of the following is true for pure noncompetitive inhibition on Lineweaver–Burk plot?

  • Lines intersect on the y-axis
  • Lines intersect on the x-axis
  • Lines are parallel
  • Lines coincide

Correct Answer: Lines intersect on the x-axis

Q22. Which enzyme inhibitor class is clinically used to increase synaptic acetylcholine in Alzheimer’s disease (reversible inhibitors)?

  • Organophosphates
  • Carbamate acetylcholinesterase inhibitors (e.g., donepezil is reversible)
  • ACE inhibitors
  • Beta-lactam antibiotics

Correct Answer: Carbamate acetylcholinesterase inhibitors (e.g., donepezil is reversible)

Q23. For an uncompetitive inhibitor, what happens to the Lineweaver–Burk lines?

  • They intersect on the y-axis
  • They intersect on the x-axis
  • They become parallel
  • They overlap exactly

Correct Answer: They become parallel

Q24. Which parameter directly describes inhibitor potency in kinetic experiments?

  • Vmax
  • Km
  • Ki
  • kcat

Correct Answer: Ki

Q25. Which inhibitor type typically shows time-dependent inhibition progress curves?

  • Fast reversible competitive inhibitors
  • Slow-binding or mechanism-based irreversible inhibitors
  • Pure noncompetitive reversible inhibitors
  • Allosteric activators

Correct Answer: Slow-binding or mechanism-based irreversible inhibitors

Q26. Which statement best describes mixed inhibition in clinical drug interactions?

  • Inhibitor only binds the free enzyme
  • Inhibitor binds both free enzyme and ES complex with different affinities
  • Inhibitor only binds the ES complex
  • Inhibitor always increases Vmax

Correct Answer: Inhibitor binds both free enzyme and ES complex with different affinities

Q27. Which experimental observation indicates competitive inhibition when varying [S]?

  • Vmax decreases even at high [S]
  • Apparent Km increases and effect is overcome by high [S]
  • Apparent Km decreases and Vmax increases
  • No change in kinetic parameters

Correct Answer: Apparent Km increases and effect is overcome by high [S]

Q28. Which drug type acts as an irreversible inhibitor of monoamine oxidase (MAO)?

  • Selective reversible MAO-A inhibitors only
  • Hydrazine and some phenelzine-like irreversible inhibitors
  • ACE inhibitors
  • Proton pump inhibitors

Correct Answer: Hydrazine and some phenelzine-like irreversible inhibitors

Q29. Which method helps determine whether an inhibitor is competitive versus noncompetitive using kinetics?

  • Measure enzyme thermal stability only
  • Compare Lineweaver–Burk plots at different [I] and [S]
  • Mass spectrometry of substrate only
  • Thin layer chromatography of products

Correct Answer: Compare Lineweaver–Burk plots at different [I] and [S]

Q30. Which factor must be considered when translating in vitro inhibition data to clinical drug interactions?

  • Only the in vitro Ki value without context
  • In vivo inhibitor concentration, protein binding, and enzyme expression
  • Only the Vmax measured in vitro
  • Only the Michaelis constant from a single experiment

Correct Answer: In vivo inhibitor concentration, protein binding, and enzyme expression

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