Enzymology — MCQs Biology – T4Tutorials .PK

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1. Enzymes are primarily:
(A) Structural molecules
(B) Hormones
(C) Energy storage molecules
(D) Biological catalysts

2. The substrate binds to the enzyme at the:
(A) Inhibitor site
(B) Allosteric site
(C) Active site
(D) Cofactor site

3. Enzyme activity is influenced by:
(A) Temperature
(B) All of the above
(C) Substrate concentration
(D) pH

4. Cofactors are:
(A) Competitive inhibitors
(B) Substrates
(C) Products
(D) Non-protein molecules that assist enzyme activity

5. Coenzymes are:
(A) Organic cofactors
(B) Protein molecules
(C) Inorganic ions
(D) Substrates

6. Competitive inhibitors:
(A) Bind to the enzyme’s active site
(B) Bind to an allosteric site
(C) Enhance enzyme activity
(D) Denature the enzyme

7. Non-competitive inhibitors:
(A) Bind to the active site
(B) Bind to an allosteric site and reduce activity
(C) Increase substrate affinity
(D) Are coenzymes

8. Michaelis-Menten constant (Km) represents:
(A) Substrate concentration at half-maximal velocity
(B) Maximum velocity of enzyme
(C) Inhibitor concentration
(D) Enzyme concentration

9. Vmax refers to:
(A) Substrate concentration
(B) Maximum reaction rate
(C) Km
(D) Inhibitor binding constant

10. Allosteric enzymes:
(A) Both B and C
(B) Have multiple subunits and regulatory sites
(C) Do not follow Michaelis-Menten kinetics
(D) Are inhibited by competitive inhibitors only

11. Enzyme specificity refers to:
(A) Ability to catalyze multiple reactions
(B) Cofactor requirement
(C) Ability to denature
(D) Ability to bind to a specific substrate

12. The induced-fit model suggests:
(A) Active site changes shape to fit substrate
(B) Enzyme active site is rigid
(C) Substrate changes shape only
(D) Enzyme denatures after binding

13. The lock-and-key model suggests:
(A) Enzyme changes shape
(B) Substrate fits perfectly into enzyme active site
(C) Substrate changes shape
(D) Cofactors are not required

14. Enzyme units (U) measure:
(A) Protein concentration
(B) Substrate concentration
(C) Rate of reaction under defined conditions
(D) Inhibitor potency

15. Enzyme turnover number (kcat) refers to:
(A) Substrate affinity
(B) Number of inhibitors bound
(C) Molecular weight of enzyme
(D) Substrate molecules converted per enzyme molecule per second

16. Irreversible inhibitors:
(A) Bind covalently to enzyme and inactivate it
(B) Bind temporarily
(C) Increase enzyme activity
(D) Compete with substrate

17. Zymogens are:
(A) Active enzymes
(B) Competitive inhibitors
(C) Inactive enzyme precursors
(D) Substrates

18. Examples of zymogens include:
(A) Pepsinogen, trypsinogen
(B) Lactase, amylase
(C) Hexokinase, glucokinase
(D) Lipase only

19. Isoenzymes (isozymes) are:
(A) Different enzymes catalyzing same reaction
(B) Same enzymes in different organisms
(C) Inactive forms of enzymes
(D) Substrate analogs

20. Lineweaver-Burk plot is used to:
(A) Measure enzyme denaturation
(B) Sequence proteins
(C) Determine Km and Vmax
(D) Calculate substrate concentration

21. Enzymes accelerate reactions by:
(A) Increasing activation energy
(B) Increasing substrate concentration only
(C) Lowering activation energy
(D) Denaturing the substrate

22. Lyases catalyze:
(A) Oxidation-reduction reactions
(B) Addition or removal of groups to form double bonds
(C) Hydrolysis reactions
(D) Isomerization reactions

23. Transferases catalyze:
(A) Transfer of functional groups between molecules
(B) Addition of water
(C) Oxidation only
(D) Protein folding

24. Hydrolases catalyze:
(A) Oxidation reactions
(B) Transfer reactions
(C) Isomerization reactions
(D) Hydrolysis reactions

25. Oxidoreductases catalyze:
(A) Oxidation-reduction reactions
(B) Hydrolysis reactions
(C) Transfer reactions
(D) Isomerization reactions

26. Isomerases catalyze:
(A) Structural rearrangements within a molecule
(B) Transfer of groups
(C) Oxidation
(D) Hydrolysis

27. Ligases catalyze:
(A) Oxidation
(B) Hydrolysis
(C) Joining of two molecules with ATP hydrolysis
(D) Isomerization

28. Enzyme inhibition can be reversed by:
(A) Both A and B
(B) Removing non-competitive inhibitor
(C) Increasing substrate concentration in competitive inhibition
(D) Neither

29. Allosteric regulation involves:
(A) Binding of regulator to active site
(B) Substrate phosphorylation
(C) Denaturation of enzyme
(D) Binding of regulator to allosteric site

30. Positive allosteric effectors:
(A) Inhibit enzyme activity
(B) Enhance enzyme activity
(C) Denature enzyme
(D) Serve as competitive inhibitors

31. Negative allosteric effectors:
(A) Enhance enzyme activity
(B) Denature substrate
(C) Inhibit enzyme activity
(D) Act as coenzymes

32. Enzyme kinetics studies:
(A) Protein structure
(B) Rate of chemical reactions catalyzed by enzymes
(C) DNA sequences
(D) RNA transcription

33. Proteolytic enzymes include:
(A) Amylase and lipase
(B) Hexokinase only
(C) Pepsin, trypsin, chymotrypsin
(D) Lactase only

34. Lipolytic enzymes include:
(A) Amylase
(B) Nuclease
(C) Protease
(D) Lipase

35. Glycolytic enzymes include:
(A) Lipase only
(B) Pepsin, trypsin
(C) Hexokinase, phosphofructokinase, pyruvate kinase
(D) Nuclease only

36. Km value is inversely proportional to:
(A) Enzyme denaturation
(B) Vmax
(C) Substrate concentration
(D) Enzyme affinity for substrate

37. Feedback inhibition is a form of:
(A) Allosteric regulation
(B) Non-competitive inhibition
(C) Competitive inhibition
(D) Substrate activation

38. Enzyme units (U) are defined as:
(A) Total mass of enzyme
(B) Amount of enzyme that catalyzes 1 µmol of substrate per minute
(C) Concentration of substrate
(D) Rate of denaturation

39. Enzymes are mostly:
(A) Nucleic acids
(B) Lipids
(C) Carbohydrates
(D) Proteins

40. Ribozymes are:
(A) Protein enzymes
(B) DNA-binding proteins
(C) RNA molecules with catalytic activity
(D) Coenzymes

41. Enzymes can be denatured by:
(A) Extreme pH
(B) High temperature
(C) All of the above
(D) Organic solvents

42. Temperature optimum refers to:
(A) Temperature at which enzyme activity is maximal
(B) Temperature at which enzyme denatures
(C) Temperature at which substrate binds
(D) Storage temperature

43. pH optimum refers to:
(A) pH at which enzyme denatures
(B) pH at which substrate is inactive
(C) pH at which enzyme activity is maximal
(D) pH of buffer only

44. Isozymes allow:
(A) Denaturation of enzymes
(B) Enzyme function in different tissues or conditions
(C) Cofactor binding only
(D) Substrate inhibition

45. Enzyme-substrate complex formation is explained by:
(A) Lock-and-key model
(B) Both A and B
(C) Induced-fit model
(D) Neither

46. Km is a measure of:
(A) Enzyme turnover number
(B) Enzyme-substrate affinity
(C) Maximum velocity
(D) Inhibitor concentration

47. Lineweaver-Burk plot is a plot of:
(A) V vs 1/[S]
(B) V vs [S]
(C) 1/V vs 1/[S]
(D) 1/V vs [S]

48. Enzyme induction refers to:
(A) Increase in enzyme synthesis due to substrate presence
(B) Decrease in enzyme synthesis
(C) Enzyme inhibition
(D) Enzyme denaturation

49. Enzyme repression refers to:
(A) Increase in enzyme synthesis
(B) Denaturation of enzyme
(C) Decrease in enzyme synthesis due to end-product
(D) Activation of enzyme

50. The coenzyme NAD+ is derived from:
(A) Vitamin C
(B) Vitamin B2
(C) Vitamin B12
(D) Vitamin B3 (Niacin)