General properties of enzymes MCQs With Answer

This collection of MCQs on “General Properties of Enzymes” is designed specifically for M.Pharm students preparing for advanced pharmaceutical biotechnology examinations. The questions focus on fundamental and applied aspects of enzyme behavior — including catalytic mechanisms, kinetics, specificity, regulation, stability, and the influence of physicochemical factors. Each item emphasizes conceptual understanding and interpretation of enzyme parameters such as Km, Vmax, kcat, and catalytic efficiency, as well as practical implications for drug development, enzyme assays, immobilization, and inhibition. Use these questions to test depth of knowledge, refine problem-solving skills, and reinforce links between enzyme theory and pharmaceutical applications.

Q1. Which property best defines catalytic efficiency of an enzyme under conditions where substrate concentration is much lower than Km?

• Vmax
• Km
• kcat/Km
• Turnover number (kcat)

Correct Answer: kcat/Km

Q2. In Michaelis–Menten kinetics, which assumption is essential for deriving the steady-state equation?

• Product formation is irreversible
• The enzyme–substrate complex concentration rapidly reaches a steady state
• Substrate concentration is always lower than enzyme concentration
• The active site is identical in all enzyme molecules

Correct Answer: The enzyme–substrate complex concentration rapidly reaches a steady state

Q3. Which type of inhibitor increases the apparent Km but does not change Vmax in reversible inhibition?

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

Correct Answer: Competitive inhibitor

Q4. Which parameter specifically describes the maximum number of substrate molecules converted to product per active site per second when the enzyme is saturated?

• Kcat
• Km
• Vmax
• Catalytic efficiency

Correct Answer: Kcat

Q5. Which statement best explains the significance of Km for a drug-metabolizing enzyme in pharmacokinetics?

• Km indicates the maximum rate of metabolism independent of substrate concentration
• Km is inversely proportional to enzyme turnover number
• Km approximates the substrate concentration at which the metabolic rate is half-maximal and reflects enzyme affinity
• Km determines the irreversible inhibition susceptibility

Correct Answer: Km approximates the substrate concentration at which the metabolic rate is half-maximal and reflects enzyme affinity

Q6. Which change is most likely when an enzyme is immobilized on a solid support compared to free enzyme in solution?

• Increased susceptibility to proteolytic degradation
• Often reduced apparent Km due to enhanced substrate diffusion
• Potential decrease in apparent catalytic turnover (kcat) and increased operational stability
• Complete loss of stereospecificity

Correct Answer: Potential decrease in apparent catalytic turnover (kcat) and increased operational stability

Q7. Which factor most commonly causes a bell-shaped pH-activity profile for many enzymes?

• Change in primary amino acid sequence with pH
• Ionization states of essential active-site residues affecting substrate binding and catalysis
• Thermal denaturation at extreme pH values only
• Alteration in molecular weight of the enzyme

Correct Answer: Ionization states of essential active-site residues affecting substrate binding and catalysis

Q8. Which description best fits an apoenzyme?

• An enzyme covalently bound to its substrate
• The protein component of an enzyme lacking its required cofactor
• An enzyme in the fully active holoenzyme form
• A zymogen or inactive precursor

Correct Answer: The protein component of an enzyme lacking its required cofactor

Q9. Which mechanism explains allosteric regulation in many multi-subunit enzymes?

• Active site mutation causing permanent activation
• Conformational change transmitted between subunits altering affinity or activity
• Proteolytic cleavage leading to isoenzyme formation
• Simple competitive binding at the active site only

Correct Answer: Conformational change transmitted between subunits altering affinity or activity

Q10. Which experiment or plot is most appropriate to determine Vmax and Km when enzyme data contain experimental error at low substrate concentrations?

• Substrate saturation curve only
• Lineweaver–Burk double reciprocal plot
• Eadie–Hofstee or Hanes–Woolf plot to reduce weighting of low [S] error
• Direct measurement of kcat without plotting

Correct Answer: Eadie–Hofstee or Hanes–Woolf plot to reduce weighting of low [S] error

Q11. Which property differentiates isoenzymes (isozymes) in drug metabolism?

• They are identical proteins with identical kinetic parameters
• They catalyze different biochemical reactions entirely
• They are different molecular forms of an enzyme with distinct kinetic and regulatory properties
• They are only produced under pathological conditions

Correct Answer: They are different molecular forms of an enzyme with distinct kinetic and regulatory properties

Q12. Which statement best characterizes irreversible enzyme inhibitors in a pharmaceutical context?

• They bind weakly and can be outcompeted by high substrate levels
• They form covalent or extremely tight non-covalent interactions leading to permanent loss of activity
• They always increase Km without affecting Vmax
• They only interact with allosteric sites

Correct Answer: They form covalent or extremely tight non-covalent interactions leading to permanent loss of activity

Q13. How does increasing temperature typically affect enzyme-catalyzed reaction rates below the enzyme’s optimum?

• Reaction rate decreases exponentially with temperature increase
• Rate increases due to higher molecular collisions and activation overcoming, often following Arrhenius behavior until denaturation
• No change in rate until a threshold temperature
• Complete inactivation immediately upon slight temperature rise

Correct Answer: Rate increases due to higher molecular collisions and activation overcoming, often following Arrhenius behavior until denaturation

Q14. Which kinetic signature indicates uncompetitive inhibition when plotting Lineweaver–Burk data?

• Lines intersect at the y-axis
• Parallel lines with both Vmax and Km decreased
• Lines intersect at x-axis indicating increased Vmax only
• All lines converge at a single point left of the y-axis

Correct Answer: Parallel lines with both Vmax and Km decreased

Q15. What is the most appropriate explanation for substrate channeling in multi-enzyme complexes?

• Substrates freely diffuse away between enzyme steps
• Direct transfer of intermediate from one active site to next reduces transit time and protects labile intermediates
• It always increases Km for each enzyme in the pathway
• It requires covalent linkage between substrates

Correct Answer: Direct transfer of intermediate from one active site to next reduces transit time and protects labile intermediates

Q16. Which effect does a non-competitive inhibitor have on enzyme kinetics when pure non-competitive binding occurs?

• Increases Km, decreases Vmax
• Decreases Km, increases Vmax
• Decreases Vmax without changing Km
• Increases both Km and Vmax

Correct Answer: Decreases Vmax without changing Km

Q17. Which molecular change is typically responsible for reversible covalent regulation of enzyme activity in signaling pathways?

• Proteolytic cleavage to form a zymogen
• Oxidative damage to the active site
• Phosphorylation / dephosphorylation of specific residues
• Permanent glycosylation of the protein backbone

Correct Answer: Phosphorylation / dephosphorylation of specific residues

Q18. Which parameter would you measure to assess thermal stability of an enzyme preparation intended for biocatalysis?

• Km at a single temperature
• Tm (melting temperature) and half-life of activity at operational temperature
• Only kcat at room temperature
• Isoelectric point (pI) alone

Correct Answer: Tm (melting temperature) and half-life of activity at operational temperature

Q19. Which characteristic defines stereospecificity of enzymes relevant to drug metabolism?

• Ability to catalyze reactions irrespective of substrate stereochemistry
• Preference for one enantiomer or stereoisomer over another, influencing metabolic fate and pharmacology
• Only applies to achiral substrates
• Stereospecificity is irrelevant in biological systems

Correct Answer: Preference for one enantiomer or stereoisomer over another, influencing metabolic fate and pharmacology

Q20. Which practical consideration is most important when designing an in vitro enzyme assay to determine Km accurately?

• Use substrate concentrations only much higher than expected Km
• Ensure measurements are taken under initial-rate conditions with substrate concentrations spanning below and above Km and minimal product accumulation
• Run assays until complete substrate depletion to measure total turnover
• Always include irreversible inhibitors to stabilize the enzyme

Correct Answer: Ensure measurements are taken under initial-rate conditions with substrate concentrations spanning below and above Km and minimal product accumulation

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