Properties of enzymes MCQs With Answer

Understanding Properties of enzymes MCQs With Answer is essential for B. Pharm students preparing for biochemistry, pharmacology, and pharmaceutical research. This concise, exam-focused introduction highlights enzyme structure and active site chemistry, catalytic mechanisms, kinetic parameters (Km, Vmax, kcat), substrate specificity, cofactors and coenzymes, pH and temperature effects, inhibition types, allosteric regulation, and zymogen activation. Emphasis on Michaelis–Menten kinetics, Lineweaver–Burk analysis, enzyme assays, and clinical relevance helps students tackle numerical problems and drug–enzyme interactions. Targeted practice with MCQs builds analytical skills crucial for drug development and therapeutics. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What term describes the maximum rate achieved by an enzyme when saturated with substrate?

• Km
• Vmax
• kcat/Km
• Turnover time

Correct Answer: Vmax

Q2. Which parameter represents the substrate concentration at which reaction rate is half of Vmax?

• kcat
• Km
• Vmax
• Ki

Correct Answer: Km

Q3. kcat is best described as:

• The enzyme concentration required for half-maximal velocity
• The catalytic constant or turnover number per active site
• The inhibitor constant
• The Michaelis constant per substrate molecule

Correct Answer: The catalytic constant or turnover number per active site

Q4. Which plot linearizes the Michaelis–Menten equation by plotting 1/V against 1/[S]?

• Michaelis plot
• Lineweaver–Burk plot
• Eadie–Hofstee plot
• Hanes–Woolf plot

Correct Answer: Lineweaver–Burk plot

Q5. Competitive inhibition is characterized by which effect on Km and Vmax?

• Km increases, Vmax unchanged
• Km decreases, Vmax decreases
• Km unchanged, Vmax decreases
• Km decreases, Vmax unchanged

Correct Answer: Km increases, Vmax unchanged

Q6. Noncompetitive inhibition typically results in:

• Increased Vmax and unchanged Km
• Decreased Vmax and increased Km
• Decreased Vmax and unchanged Km
• Unchanged Vmax and decreased Km

Correct Answer: Decreased Vmax and unchanged Km

Q7. An enzyme that requires a metal ion for activity is called a:

• Coenzyme
• Prosthetic group
• Metalloenzyme
• Zymogen

Correct Answer: Metalloenzyme

Q8. NAD+ functions in enzymes primarily as a:

• Metal cofactor
• Prosthetic group tightly bound to protein
• Diffusible coenzyme for redox reactions
• Allosteric inhibitor

Correct Answer: Diffusible coenzyme for redox reactions

Q9. Which mechanism is NOT a common catalytic strategy used by enzymes?

• Acid–base catalysis
• Catalysis by proximity and orientation
• Photocatalysis requiring light
• Covalent catalysis

Correct Answer: Photocatalysis requiring light

Q10. The induced-fit model of enzyme action proposes that:

• Enzyme and substrate have rigid complementary shapes
• Substrate induces conformational change in the enzyme
• Enzymes act only at a fixed pH
• Substrate permanently binds as a covalent adduct

Correct Answer: Substrate induces conformational change in the enzyme

Q11. Allosteric enzymes often display which kinetic behavior?

• Hyperbolic Michaelis–Menten kinetics
• Linear kinetics with substrate concentration
• Sigmoidal kinetics indicating cooperativity
• Zero-order kinetics at all substrate levels

Correct Answer: Sigmoidal kinetics indicating cooperativity

Q12. The Hill coefficient greater than 1 indicates:

• Negative cooperativity
• No cooperativity
• Positive cooperativity
• Irreversible inhibition

Correct Answer: Positive cooperativity

Q13. Which term describes an inactive enzyme precursor activated by proteolytic cleavage?

• Isoenzyme
• Zymogen (proenzyme)
• Allosteric enzyme
• Holoenzyme

Correct Answer: Zymogen (proenzyme)

Q14. Isoenzymes are important clinically because:

• They are identical proteins with no diagnostic use
• They allow tissue-specific diagnostics based on different enzyme forms
• They always require coenzymes to function
• They irreversibly bind substrates

Correct Answer: They allow tissue-specific diagnostics based on different enzyme forms

Q15. Which method is commonly used to measure enzyme activity by monitoring product formation spectrophotometrically?

• Chromatography
• UV–Vis absorbance assay
• Electrophoresis
• Fluorescence in situ hybridization

Correct Answer: UV–Vis absorbance assay

Q16. A suicide inhibitor is best described as:

• A reversible competitive inhibitor
• An irreversible inhibitor that is converted by the enzyme into a reactive species
• An inhibitor that increases Km
• A noncompetitive reversible inhibitor

Correct Answer: An irreversible inhibitor that is converted by the enzyme into a reactive species

Q17. Which factor most commonly causes enzyme denaturation and loss of activity?

• Optimal pH
• Excess temperature causing unfolding
• Presence of substrates
• Cooperative binding

Correct Answer: Excess temperature causing unfolding

Q18. Vmax normalized per enzyme concentration gives which parameter?

• Km
• Specific activity
• kcat
• Turnover time

Correct Answer: kcat

Q19. The Michaelis–Menten equation assumes which key condition?

• Product formation rate is independent of enzyme concentration
• Steady-state where ES concentration is constant relative to initial phase
• Equilibrium between enzyme and product only
• Substrate concentration is always less than Km

Correct Answer: Steady-state where ES concentration is constant relative to initial phase

Q20. In uncompetitive inhibition, the inhibitor binds:

• Only to free enzyme
• Only to the enzyme–substrate complex
• Equally to enzyme and ES complex
• To the substrate before enzyme binding

Correct Answer: Only to the enzyme–substrate complex

Q21. Which describes a holoenzyme?

• Enzyme without its cofactor
• Complete enzyme with its prosthetic group or cofactor bound
• Inactive zymogen
• Denatured enzyme aggregate

Correct Answer: Complete enzyme with its prosthetic group or cofactor bound

Q22. Which is an example of a prosthetic group?

• NADH
• ATP
• Heme in cytochromes
• Glucose

Correct Answer: Heme in cytochromes

Q23. Which statement about Km is true?

• Lower Km means lower affinity for substrate
• Km equals Vmax at half enzyme concentration
• Lower Km indicates higher substrate affinity
• Km is independent of enzyme–substrate affinity

Correct Answer: Lower Km indicates higher substrate affinity

Q24. Transition state stabilization by an enzyme lowers which barrier?

• Activation energy
• Entropy of substrate
• Product energy below reactants
• Temperature requirement to zero

Correct Answer: Activation energy

Q25. Which catalytic mechanism involves temporary covalent bond formation between enzyme and substrate?

• Acid–base catalysis
• Covalent catalysis
• Metal-ion catalysis
• Proximity and orientation

Correct Answer: Covalent catalysis

Q26. Immobilized enzymes are used in industry mainly because they:

• Have unlimited stability
• Are easier to separate and reuse and often show improved stability
• Do not require cofactors
• Have higher Km always

Correct Answer: Are easier to separate and reuse and often show improved stability

Q27. Which kinetic plot is least sensitive to experimental error at low substrate concentrations?

• Lineweaver–Burk plot
• Eadie–Hofstee plot
• Michaelis plot
• Hanes–Woolf plot

Correct Answer: Hanes–Woolf plot

Q28. The effect of pH on enzyme activity is primarily due to:

• Changes in substrate structure only
• Ionization states of active site residues and substrate
• Temperature fluctuations
• Viscosity change of solution

Correct Answer: Ionization states of active site residues and substrate

Q29. Which enzyme class catalyzes oxidation–reduction reactions?

• Hydrolases
• Oxidoreductases
• Transferases
• Ligases

Correct Answer: Oxidoreductases

Q30. Inhibition constant Ki is best defined as:

• The maximum velocity of the inhibited enzyme
• Equilibrium constant for inhibitor binding to enzyme
• The Michaelis constant in presence of inhibitor
• Turnover number of inhibitor

Correct Answer: Equilibrium constant for inhibitor binding to enzyme

Q31. Which describes substrate specificity of trypsin?

• Cleaves after aromatic residues only
• Cleaves peptide bonds after positively charged residues like Lys or Arg
• Cleaves at random peptide bonds
• Only hydrolyzes ester bonds

Correct Answer: Cleaves peptide bonds after positively charged residues like Lys or Arg

Q32. Which statement about reversible inhibitors is correct?

• They permanently inactivate the enzyme
• They bind non-covalently and can dissociate
• They always act at the active site only
• They always increase enzyme activity

Correct Answer: They bind non-covalently and can dissociate

Q33. Enzyme specificity due to complementarity between enzyme and substrate was originally described by:

• Induced-fit model
• Lock-and-key model
• Michaelis–Menten theory
• Lineweaver and Burk

Correct Answer: Lock-and-key model

Q34. Which factor increases reaction rate by bringing substrate molecules close to the active site?

• Allosteric inhibition
• Proximity and orientation effect
• Denaturation
• Competitive inhibition

Correct Answer: Proximity and orientation effect

Q35. A bisubstrate enzyme that transfers a group from donor A to acceptor B is classified as a:

• Hydrolase
• Transferase
• Isomerase
• Ligase

Correct Answer: Transferase

Q36. Which clinical implication relates to enzyme inhibition in drug therapy?

• Inhibition always cures disease
• Selective enzyme inhibitors can reduce pathogenic pathways or modulate metabolism of drugs
• Enzyme inhibition never affects drug metabolism
• All enzyme inhibitors are toxic

Correct Answer: Selective enzyme inhibitors can reduce pathogenic pathways or modulate metabolism of drugs

Q37. Which term describes enzyme activity per milligram of protein?

• Turnover number
• Specific activity
• Km value
• Isoenzyme index

Correct Answer: Specific activity

Q38. Competitive inhibitors resemble substrate and bind to:

• Allosteric site only
• Active site preventing substrate binding
• ES complex only
• The product binding site

Correct Answer: Active site preventing substrate binding

Q39. Which enzyme kinetic term combines catalytic efficiency and substrate affinity?

• Vmax
• kcat/Km
• Ki
• Km/Vmax

Correct Answer: kcat/Km

Q40. Which regulatory mechanism involves phosphorylation to modulate enzyme activity?

• Proteolytic cleavage only
• Covalent modification by kinases and phosphatases
• Allosteric ligand binding only
• Isoform switching

Correct Answer: Covalent modification by kinases and phosphatases

Q41. Enzyme turnover number depends primarily on:

• Substrate molecular weight
• Intrinsic catalytic speed of the active site when saturated
• Buffer composition only
• Temperature only

Correct Answer: Intrinsic catalytic speed of the active site when saturated

Q42. Which analytical technique separates enzyme isoforms based on charge differences?

• Size-exclusion chromatography
• Ion-exchange chromatography or isoelectric focusing
• Mass spectrometry only
• Southern blotting

Correct Answer: Ion-exchange chromatography or isoelectric focusing

Q43. Enzyme assay conditions are usually set to measure initial velocity because:

• Initial velocity reflects steady-state and avoids complications from product inhibition or reverse reactions
• Later times are more accurate
• Substrate becomes irrelevant later
• Product concentration is zero initially

Correct Answer: Initial velocity reflects steady-state and avoids complications from product inhibition or reverse reactions

Q44. Which type of enzyme inhibition can be overcome by increasing substrate concentration?

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

Correct Answer: Competitive inhibition

Q45. Metal ions in metalloenzymes often assist catalysis by:

• Only acting as structural scaffolds without participating in chemistry
• Stabilizing negative charges, acting as electrophiles, or aiding redox chemistry
• Increasing Km to very high values
• Denaturing substrates

Correct Answer: Stabilizing negative charges, acting as electrophiles, or aiding redox chemistry

Q46. Which process converts an inactive precursor to an active enzyme in digestive systems?

• Allosteric inhibition
• Proteolytic activation of zymogens
• Phosphorylation by kinases
• Glycosylation in Golgi only

Correct Answer: Proteolytic activation of zymogens

Q47. Which property is characteristic of enzyme-catalyzed reactions compared to uncatalyzed reactions?

• Higher activation energy
• Lower activation energy and higher specific reaction rate
• Changed equilibrium constant favoring products always
• Irreversible conversion only

Correct Answer: Lower activation energy and higher specific reaction rate

Q48. Which of the following is a diagnostic marker released into blood after myocardial infarction and exists as isoenzymes?

• Amylase
• Creatine kinase (CK-MB isoenzyme)
• Alkaline phosphatase only
• Lactase

Correct Answer: Creatine kinase (CK-MB isoenzyme)

Q49. The effect of temperature on enzyme-catalyzed reaction rate typically shows:

• A linear increase without limit
• An increase to an optimum then rapid decline due to denaturation
• No change with temperature
• Instant irreversible activation at high temperature

Correct Answer: An increase to an optimum then rapid decline due to denaturation

Q50. In drug design, transition-state analogs act as potent inhibitors because they:

• Mimic substrate ground state
• Bind more tightly to the enzyme by resembling the transition state
• Are always irreversible inhibitors
• Increase enzyme turnover

Correct Answer: Bind more tightly to the enzyme by resembling the transition state

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