Enzyme kinetics – Michaelis-Menten plot MCQs With Answer

Enzyme kinetics – Michaelis-Menten plot MCQs With Answer
Understanding enzyme kinetics is essential for B.Pharm students studying drug action, metabolism, and enzyme inhibition. This concise guide focuses on the Michaelis-Menten plot, key parameters like Km and Vmax, catalytic efficiency (kcat/Km), and graphical methods such as Lineweaver-Burk and Eadie-Hofstee. Clear explanations of enzyme-substrate complex formation, steady-state assumptions, and inhibitor effects help bridge theory and practical pharmacology. These MCQs emphasize data interpretation, experimental design, and clinical relevance—preparing you for exams and research. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which equation represents the Michaelis-Menten relationship between initial velocity (v0) and substrate concentration [S]?

• v0 = Vmax[S] / (Km + [S])
• v0 = Km[S] / (Vmax + [S])
• v0 = Vmax / (Km + [S])
• v0 = kcat[E]t[S] / (Km + [S])

Correct Answer: v0 = Vmax[S] / (Km + [S])

Q2. In Michaelis-Menten kinetics, what does Km represent?

• The substrate concentration where v0 = Vmax
• The substrate concentration where v0 = Vmax/2
• The maximum velocity of the enzyme
• The catalytic turnover number

Correct Answer: The substrate concentration where v0 = Vmax/2

Q3. How is Vmax related to kcat and total enzyme concentration [E]t?

• Vmax = Km × [E]t
• Vmax = kcat × [E]t
• Vmax = kcat / [E]t
• Vmax = kcat + [E]t

Correct Answer: Vmax = kcat × [E]t

Q4. Which plot is a double-reciprocal representation of the Michaelis-Menten equation?

• Eadie-Hofstee plot
• Lineweaver-Burk plot
• Hanes-Woolf plot
• Scatchard plot

Correct Answer: Lineweaver-Burk plot

Q5. On a Lineweaver-Burk plot (1/v versus 1/[S]), what does the y-intercept equal?

• 1/Km
• Km/Vmax
• 1/Vmax
• Vmax

Correct Answer: 1/Vmax

Q6. What is the slope of the Lineweaver-Burk plot equal to?

• Km/Vmax
• Vmax/Km
• kcat/[E]t
• 1/(Km × Vmax)

Correct Answer: Km/Vmax

Q7. Which plot has the advantage of uniform error distribution and plots [S]/v versus [S]?

• Lineweaver-Burk plot
• Eadie-Hofstee plot
• Hanes-Woolf plot
• Scatchard plot

Correct Answer: Hanes-Woolf plot

Q8. In an Eadie-Hofstee plot, what are the axes?

• v on x-axis and v/[S] on y-axis
• v/[S] on x-axis and v on y-axis
• v on x-axis and [S] on y-axis
• 1/v on x-axis and 1/[S] on y-axis

Correct Answer: v on x-axis and v/[S] on y-axis

Q9. Which assumption is central to the classical Michaelis-Menten derivation?

• Product inhibition is dominant
• Steady-state approximation for [ES]
• Substrate concentration is always lower than enzyme concentration
• kcat is equal to zero

Correct Answer: Steady-state approximation for [ES]

Q10. Briggs-Haldane formulation differs from the rapid equilibrium assumption by assuming:

• Rapid equilibrium between E and S
• Steady state for ES without rapid equilibrium
• No formation of ES complex
• Product binds irreversibly

Correct Answer: Steady state for ES without rapid equilibrium

Q11. Which parameter indicates catalytic efficiency of an enzyme?

• Km only
• Vmax only
• kcat/Km
• kcat × Km

Correct Answer: kcat/Km

Q12. A low Km value indicates:

• Low affinity of enzyme for substrate
• High affinity of enzyme for substrate
• High turnover number
• Low catalytic efficiency

Correct Answer: High affinity of enzyme for substrate

Q13. Competitive inhibition affects which Michaelis-Menten parameter?

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

Correct Answer: Km increases, Vmax unchanged

Q14. Noncompetitive inhibition typically results in:

• Decrease in Vmax with no change in Km
• Increase in Km with no change in Vmax
• Increase in both Km and Vmax
• Decrease in Km and increase in Vmax

Correct Answer: Decrease in Vmax with no change in Km

Q15. Uncompetitive inhibitors bind:

• Only to free enzyme
• Only to the ES complex
• To both free enzyme and ES complex equally
• Irreversibly to product

Correct Answer: Only to the ES complex

Q16. In the presence of a reversible competitive inhibitor, how does the Lineweaver-Burk plot change?

• Lines intersect on the y-axis
• Lines are parallel
• Lines intersect on x-axis
• Y-intercept increases while slope decreases

Correct Answer: Lines intersect on the y-axis

Q17. Which experimental condition ensures valid initial rate (v0) measurement?

• Significant product accumulation during measurement
• Substrate depletion is negligible during initial time
• Enzyme concentration exceeds substrate concentration
• Reaction measured after equilibrium

Correct Answer: Substrate depletion is negligible during initial time

Q18. kcat is defined as:

• Rate constant for ES formation
• Number of substrate molecules converted per enzyme molecule per second
• Equilibrium constant for enzyme-substrate binding
• Maximum substrate concentration

Correct Answer: Number of substrate molecules converted per enzyme molecule per second

Q19. Which of the following is true for a pure noncompetitive inhibitor?

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

Correct Answer: Vmax decreases and Km unchanged

Q20. How does an uncompetitive inhibitor affect Km and Vmax?

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

Correct Answer: Km decreases, Vmax decreases proportionally

Q21. Which plot often amplifies experimental error at low substrate concentrations?

• Hanes-Woolf plot
• Eadie-Hofstee plot
• Lineweaver-Burk plot
• Michaelis-Menten plot

Correct Answer: Lineweaver-Burk plot

Q22. The turnover number kcat can be determined by:

• Dividing Km by Vmax
• Multiplying Km by [E]t
• Dividing Vmax by total enzyme concentration [E]t
• Subtracting Vmax from Km

Correct Answer: Dividing Vmax by total enzyme concentration [E]t

Q23. Catalytic perfection refers to enzymes with kcat/Km values approaching:

• 10^2 M^-1 s^-1
• 10^4 M^-1 s^-1
• 10^8 – 10^9 M^-1 s^-1
• 10^-3 M^-1 s^-1

Correct Answer: 10^8 – 10^9 M^-1 s^-1

Q24. If substrate concentration [S] << Km, the Michaelis-Menten equation simplifies to:

• v0 ≈ Vmax
• v0 ≈ (Vmax/Km) × [S]
• v0 ≈ Km × [S]
• v0 ≈ Vmax × Km

Correct Answer: v0 ≈ (Vmax/Km) × [S]

Q25. Which enzyme kinetics parameter is most directly related to drug potency when enzyme is drug target?

• Vmax
• Km
• kcat/Km
• Michaelis constant of product

Correct Answer: kcat/Km

Q26. Inhibition constant Ki describes:

• Affinity between enzyme and substrate
• Affinity between enzyme and inhibitor
• Maximum reaction velocity
• Turnover number

Correct Answer: Affinity between enzyme and inhibitor

Q27. For a two-substrate enzyme following Michaelis-Menten kinetics, apparent Km for one substrate can change due to:

• Change in pH only
• Concentration of the second substrate
• Temperature only
• Presence of product only

Correct Answer: Concentration of the second substrate

Q28. Which method reduces errors associated with double reciprocal plots?

• Using Lineweaver-Burk only
• Using nonlinear regression to fit v versus [S]
• Measuring rates at a single [S]
• Using more reciprocal points at low [S]

Correct Answer: Using nonlinear regression to fit v versus [S]

Q29. An enzyme displays sigmoidal v versus [S] curve. This suggests:

• Classic Michaelis-Menten single-site kinetics
• Cooperative binding or allosteric regulation
• Irreversible inhibition
• Artifact due to enzyme purity

Correct Answer: Cooperative binding or allosteric regulation

Q30. Which of the following is a limitation of the Michaelis-Menten model?

• It cannot describe single-substrate reactions
• It assumes steady state and non-cooperative binding
• It always accounts for allosteric effects
• It provides accurate results for irreversible inhibitors only

Correct Answer: It assumes steady state and non-cooperative binding

Q31. The initial velocity v0 is measured to avoid complications from:

• Substrate binding
• Product inhibition and reverse reaction
• Enzyme folding
• Temperature changes only

Correct Answer: Product inhibition and reverse reaction

Q32. A Lineweaver-Burk plot for uncompetitive inhibition shows:

• Parallel lines
• Lines intersecting on y-axis
• Lines intersecting on x-axis
• Converging lines at negative x-value

Correct Answer: Parallel lines

Q33. The Michaelis-Menten constant Km can be influenced by:

• Only enzyme concentration
• Temperature and pH
• Only buffer composition
• Substrate chirality only

Correct Answer: Temperature and pH

Q34. Which situation favors the rapid equilibrium assumption over steady-state?

• k-1 >> k2 (dissociation faster than catalysis)
• k2 >> k-1 (catalysis faster than dissociation)
• No ES complex formation
• Very high enzyme concentration compared to substrate

Correct Answer: k-1 >> k2 (dissociation faster than catalysis)

Q35. In drug metabolism, inhibition of CYP enzymes is often characterized by:

• Only changes in Km
• Changes in Km and/or Vmax depending on inhibition type
• No change in kinetics
• Only changes in enzyme tertiary structure

Correct Answer: Changes in Km and/or Vmax depending on inhibition type

Q36. The term “pseudo-first-order” kinetics in enzyme assays means:

• Substrate concentration is much higher than enzyme and treated as constant
• Enzyme concentration is much higher than substrate
• Reaction rate is independent of substrate concentration
• Reaction is zero-order with respect to enzyme

Correct Answer: Substrate concentration is much higher than enzyme and treated as constant

Q37. Determination of Km experimentally requires measurement of:

• Initial rates at multiple substrate concentrations
• Only one measurement at saturating substrate
• Only one measurement at zero substrate
• Equilibrium binding constant of product

Correct Answer: Initial rates at multiple substrate concentrations

Q38. If Vmax remains constant but apparent Km decreases in presence of drug, the inhibitor is likely:

• Competitive
• Noncompetitive
• Uncompetitive
• Irreversible

Correct Answer: Uncompetitive

Q39. In enzyme assays, initial rate v0 is typically proportional to:

• Square of substrate concentration at all ranges
• Substrate concentration when [S] << Km
• Substrate concentration when [S] >> Km
• Inverse of [S]

Correct Answer: Substrate concentration when [S] << Km

Q40. Which kinetic plot is less biased by error at low substrate concentrations compared to Lineweaver-Burk?

• Reciprocal plot
• Direct nonlinear regression fit
• Any double reciprocal transformation
• None, all are equally biased

Correct Answer: Direct nonlinear regression fit

Q41. Allosteric enzymes typically do NOT follow Michaelis-Menten kinetics because they:

• Are single-substrate enzymes only
• Exhibit cooperative substrate binding and sigmoidal kinetics
• Have zero catalytic activity
• Have constant activity irrespective of effectors

Correct Answer: Exhibit cooperative substrate binding and sigmoidal kinetics

Q42. Which of the following best describes V0 when [S] >> Km?

• V0 ≈ (Vmax/Km)[S]
• V0 ≈ Vmax
• V0 ≈ 0
• V0 ≈ Km

Correct Answer: V0 ≈ Vmax

Q43. In a Lineweaver-Burk plot, if two lines intersect left of the y-axis and above the x-axis, it suggests:

• Mixed inhibition
• Competitive inhibition only
• Pure noncompetitive inhibition
• No inhibition

Correct Answer: Mixed inhibition

Q44. Which experimental artifact can produce apparent non-Michaelis behavior?

• Maintaining constant temperature
• Enzyme aggregation or instability during assay
• Using purified enzyme
• Measuring initial rates only

Correct Answer: Enzyme aggregation or instability during assay

Q45. Substrate inhibition at high [S] leads to:

• Enhanced Vmax without limit
• Decrease in reaction rate at very high substrate concentrations
• No change in rate at high substrate concentrations
• Linear increase of rate with [S]

Correct Answer: Decrease in reaction rate at very high substrate concentrations

Q46. Which parameter would you change experimentally to determine if inhibition is reversible?

• Increase enzyme denaturation
• Vary inhibitor concentration and observe recovery upon dilution or removal
• Change reaction pH only
• Measure product formation at single time point

Correct Answer: Vary inhibitor concentration and observe recovery upon dilution or removal

Q47. In Michaelis-Menten kinetics, ES complex concentration at steady state is determined by:

• Only kcat value
• Rates of ES formation and breakdown (k1, k-1, k2) and [E]t and [S]
• Only [S] value
• Only Vmax value

Correct Answer: Rates of ES formation and breakdown (k1, k-1, k2) and [E]t and [S]

Q48. Which experimental approach is preferred for precise estimation of Km and Vmax from noisy data?

• Manual reading of reciprocal plot intercepts
• Nonlinear least-squares regression of the Michaelis-Menten equation
• Using only two substrate points to calculate Km and Vmax
• Plotting arbitrary transformations without statistics

Correct Answer: Nonlinear least-squares regression of the Michaelis-Menten equation

Q49. A drug acts as a mechanism-based irreversible inhibitor. Its effect on enzyme kinetics is:

• Reversible increase in Km only
• Time-dependent loss of Vmax due to permanent enzyme inactivation
• Decrease in Km with no Vmax change
• No effect on enzyme activity

Correct Answer: Time-dependent loss of Vmax due to permanent enzyme inactivation

Q50. Which statement correctly links Michaelis-Menten concepts to pharmacology?

• Km has no relevance to drug binding or enzyme-target interactions
• Understanding Km, Vmax and inhibition helps predict drug interactions and metabolism rates
• Only Vmax values are used in dose calculations
• Enzyme kinetics cannot inform drug toxicity studies

Correct Answer: Understanding Km, Vmax and inhibition helps predict drug interactions and metabolism rates

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com