Top 50 Important MCQs on Enzymes



Enzymes are the biocatalyst which enhance the rate of  biochemical reaction by decreasing activation energy. Initially, enzymes react with molecules known as substrates converting it into distinct molecules known as products. They exist in all fluids and tissues of the body. The intracellular enzymes catalyze reactions taking place in metabolic pathways.

Enzymes also have valuable industrial and medical applications. The fermenting of wine, leavening of bread, curdling of cheese, and brewing of beer, The uses of enzymes in medicine include killing disease-causing microorganisms, promoting wound healing, and diagnosing certain diseases.

All enzymes are proteins, except certain nucleic acids, called ribozymes (or catalytic RNAs),

Important MCQs on ENZYMES

1. A __________is a biocatalyst that increases the rate of the reaction without being changed.
a) Aluminum oxide
b) Silicon dioxide
c) Enzyme
d) Hydrogen peroxide

Answer : C

2. The nature of an enzyme is____
a) Lipid
b) Vitamin
c) Carbohydrate
d) Protein

Answer: (d)

3. What is an apoenzyme?
a) It is a protein portion of an enzyme
b) It is a non-protein group
c) It is a complete, biologically active conjugated enzyme
d) It is a prosthetic group

Answer : a

4. the coenzyme of riboflavin (B2)?
a) NAD or NADP
b) FAD and FMN
c) Coenzyme A
d) Thiamine pyrophosphate

Answer : b

5. In alcoholism, this enzyme is elevated?
a) acid phosphatase
b) hepatitis
c) serum glutamate pyruvate trasmittase
d) glutamyl transpeptidase

Answer: (d)

6. Which of this vitamin is associated with the coenzyme Biocytin?
a) Nicotinic acid
b) Thiamine
c) Biotin
d) Pyridoxine

Answer : c

7. With regards to enzyme action, this statement is incorrect

a) Malonate is a competitive inhibitor of succinic dehydrogenase

b) substrate binds with enzyme as its active site

c) non competitve inhibitor binds the enzyme at a site distinct from that binding the substrate

d) addition of lot of succinate does not reverse the inhibition of succinic dehydrogenase
by malonate

Answer: d)

8. What is the count of genes that determine the synthesis of one enzyme?
a) One
b) Four
c) Eight
d) Sixteen

Answer: a

9. Name the enzyme which catalyzes the oxidation-reduction reaction?
a) Transaminase
b) Glutamine synthetase
c) Phosphofructokinase
d) Oxidoreductase

Answer : d

10. What is the function of phosphorylase?
a) Transfer inorganic phosphate
b) Transfer a carboxylate group
c) Use H2O2 as the electron acceptor
d) Transfer amino group

Answer : a

11. Mark the CORRECT function of enzyme, Peptidase?
a) Cleave phosphodiester bond
b) Cleave amino bonds
c) Remove phosphate from a substrate
d) Removal of H2O

Answer : b

12. This enzyme was first isolated and purified in the form of crystals
a) Urease
b) pepsin
c) Amylase
d) Ribonuclease

Answer: a

13. Macromolecule chitin is____
a) a simple polysaccharide
b) sulphur containing polysaccharide
c) phosphorous containing polysaccharide
d) nitrogen containing polysaccharide

Answer: d

14. Which of the following reaction is catalyzed by Lyase?
a) Breaking of bonds
b) Formation of bonds
c) Intramolecular rearrangement of bonds
d) Transfer of group from one molecule to another

Answer : a

15. Which of the following is an example of ligases enzyme?
a) Mutases
b) Epimerases
c) Racemases
d) Carboxylases

Answer : d

16. What is the binding energy?
a) Free energy released in the formation of enzyme-substrate interaction
b) The energy required to form a bond
c) The energy required to bind substrate
d) It is the activation energy

Answer : a

17. Enzyme-driven metabolic pathways can be made more efficient by
a) grouping enzymes into multienzyme free-floating complexes
b) concentrating enzymes with specific cellular compartments
c) fixing enzymes into membranes so they are adjacent to each other
d) all of these

Answer: d

18. Tryptophan synthetase of E.coli, a typical bifunctional oligomeric enzyme consists of
a) a protein A and one subunit A
b) a protein designated A
c) two proteins designated A and B
d) a protein designated B

Answer: c

19. This statement about enzymes is true
a) enzymes accelerate reactions by lowering activation energy

b) enzymes are proteins whose three-dimensional form is key to their function

c) enzymes do not alter the overall change in free energy for a reaction

d) all of these

Answer: d


20. Which of the following is not a catalytic strategy for an enzyme to perform specific reaction?
a) Covalent catalysis
b) Metal ion catalysis
c) Michaelis constant
d) Acid-base catalysis

Answer : c


21. What is the SI unit of enzyme activity?
a) Km
b) Kat
c) Kcat
d) Vmax

Answer : b

22. The enzyme COX-1 is vital for human health in this way:

a) it is a chemical derivative of aspirin

b) catalyzes the hormone-production which maintains the stomach lining

c) critical for the biosynthesis of DNA

d) helps in the transportation of carbon dioxide in the blood

Answer: b

23. Which of the following is not an example of irreversible enzyme inhibitor?
a) Cyanide
b) Sarin
c) Diisopropyl phosphoflouridate (DIPF)
d) Statin drugs

Answer : d

24. Lineweaver-Burk plot is also known as______
a) Double reciprocal plot
b) Hanes-Woolf plot
c) Eadie-Hofstee plot
d) Steady-state equation

Answer : a

25. Name the enzyme which is found in tears, sweat, and an egg white?
a) Ribozyme
b) Lysozyme
c) Zymogen
d) Isozymes

Answer :b

26. What is an Isozyme?
a) Same structure, different function
b) Different structure, the same function
c) Same structure, the same function
d) Different structure, different function

Answer : b

27. Which of the following statement is/are correct about Enzyme:
a) An Enzyme is a protein and is used as a catalyst to accelerate the reaction.
b) Life would not exist without the presence of enzymes.
c) Enzymes participate in cellular metabolic processes.
d) All the above

Answer : D


28. Which enzyme is used in making Baby Foods?
a)Amylase
b)Rennin
c)Trypsin
d)None of the above

Answer. C

29. Name an enzyme that is derived from the stomachs of young ruminant animals and also used in dairy industry to produce cheese?
a) Trypsin
b) Pepsin
c) Liginase
d) Rennin

Answer : D

30. Name an enzyme that digests fat?
a)  Lipase
b) Sucrase
c)  Maltase
d)Fructose

Answer. A

31. Who coined the word enzyme?
a) Wilhelm Kuhne
b)  Alfred Russel
c)  Robert Koch
d) Rosalind Franklin

Answer. A

32. Name an enzyme which is not proteinaceous in nature?
a) Cellulases
b) Xylanases
c) Ribozyme
d) Peptidiase

Answer. C


33. The ‘lock and key hypothesis’ mechanism is related with:
A. Digestion of fat in the body
B. For enzyme specificity
C. For the formation of vacuole
D. Explosives
Ans. B

34. In humans salivary amylase enzyme breaks down starch. The optimum pH for this reaction is:
A. 6
B. 6.2
C. 6.4
D. 6.7
Ans. D

35. Inactive enzymes which are not bound to their cofactors are called
A. Apoenzymes
B. Coenzymes
C. Enzyme inhibitors
D. Holoenzymes

Answer :

36. Which enzyme is used by the biscuit manufacturers to lower the protein level of flour?
A. Amylase
B. Protease
C. Cellulase
D. Xylanase

Answer. B

37. Fat is hydrolysed by the enzyme known as
a) Trypsin
b) Lipase
c) pepsin
d) Amylase

Answer : b

38. The term apoenzyme is applicable to
a) Simple enzyme
b) Protein part of conjugate enzyme
c) Organic cofactor of a conjugate enzyme
d) Inorganic cofactor of a conjugate enzyme

Answer : b

39. Enzymes___
a) Do not require activation energy
b) Do not change requirement of activation energy
c) Increase requirement of activation energy
d) Lowest requirement of activation energy

Answer : d

40. Zymogen is
a) Enzyme poison
b) Enzyme modulator
c) Enzyme precursor
d) Enzyme inhibitor

Answer : c

41. Allosteric enzyme possesses
a) Active site and an allosteric site
b) Active site and two types of allosteric sites
c) Active site and three types of allosteric sites
d)  Three types of allosteric sites

Answer : d

42. Enzyme generally have
a) Same pH and temperature optima
b) Same pH but different temperature optima
c) Different pH but same temperature optima
d) Different pH and different temperature optima

Answer : a

43. The enzyme which forms the peptide bond is known as
a) Carbonic unhydrase
b) Peptidase
c) Carbohydrase
d) Peptidyl transferase

Answer : d

44. The enzyme, tyrosinase, is activated by
a) Iron
b) Copper
c) Zinc
d) Potassium
Answer : b 

45. Trypsin are active in
a) Acidic
b) Alkaline
c) neutral
d) None of these

Answer : b


46. Which one of the following statements regarding enzyme inhibition is correct?

a) Competitive inhibition is seen when a substrate competes with an enzyme for binding to a inhibitor protein

b) Non Competitive inhibition of an enzyme can be overcome by adding large amount of substrate

c) Non competitive efficiency inhibitors often bind to the enzyme irreversibly

d) Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme

Answer : d

47. The catalytic efficiency of two different enzymes can be compared by the__
a) Formation of the product
b) Km value
c) Molecular size of the enzymes
d) pH of optimum value

Answer : b

48. The nuclease enzyme, which begins its attack from free of a polynucleotide, is
a) Polymerase
b) kinase
c) exonclease
d) endonuclease

Answer : c

49. The enzymes enterokinase helps in the conversion of
a) Caseinogens into casein
b) Trypsinogen into trypsin
c) Pepsigenogen into pepsin
d) proteins into polypeptides

Answer : b

50. Which of the following is a typical example ‘feedback inhibition’?

a) Cyanide and cytochrome reaction

b) Sulpha drugs and folic acid synthesizer bacteria

c) allosteric inhibition of hexokinase by glucose- 6 -phosphate

d) Reaction between succinic dehydrogenase and succinic acid

Answer : c

51. Some of the enzymes, which are associated in converting fats into carbohydrates, are present in
a) liposomes
b) golgi bodies
c) glyoxysomes
d) microsomes

Answer : c

52. In which one of the following enzymes, is copper necessarily associated as an activator?
a) tyrosinase
b) Lactic dehydrogenase
c) Carbonic unhydrase
d) Trypsinase

Answer : d