Important MCQs on Enzymes

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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
Answer. 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 : A

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

MCQ on Enzymes: 
1. The specificity of the enzyme refers to the________
(1) Different cells contain different enzymes
(2) an enzyme is a special protein
(3) the enzyme has specific selectivity for the substrate
(4) The structure of the enzyme is specific
(5):the enzyme has an active center
Answer: 3 
Explanation: The specificity of an enzymatic reaction refers to the selectivity of an enzyme to a substrate. Enzymatic reactions have a high degree of specificity and can be divided into three categories: 
① Absolute specificity: the enzyme only acts on a substrate with a specific structure to generate a product with a specific structure; 
② Relative specificity: the enzyme can act on one type of compound or one type of compound. A chemical bond; 
③ Stereoisomeric specificity: An enzyme only acts on one of the stereoisomers.

2. Which of the following statements about the function of enzymes is false?
(1) The role of enzymes can only accelerate the reaction to reach the equilibrium point, but cannot change the equilibrium point
(2) the catalytic efficiency of enzymes is very high
(3) the enzymatic reaction has high specificity
(4) Enzymatic reactions are adjustable
(5) An enzyme can act on any of the stereoisomers
Answer: 5
Explanation: The common points of enzymes and general catalysts: the quality and quantity before and after the reaction remain unchanged; they only catalyze the reactions allowed by thermodynamics; they can only accelerate the process of reversible reactions without changing the equilibrium point of the reaction.
3. The statement about the active center of the enzyme is correct
(1) All enzymes have active centers
(2) All enzymes have coenzymes in their active centers
(3) All enzymes have metal ions in their active centers
(4) The essential groups of the enzyme are located in the active center
(5) All inhibitors act on the active center
Answer: 1
Explanation: Enzymes are proteins synthesized by living cells with efficient catalytic ability to specific substrates. Only if there is an active center can there be catalytic activity, it can be called an enzyme.
4. The effect of malonate on succinate dehydrogenase belongs to
(1) feedback inhibition
(2) Substrate inhibition
(3) Competitive inhibition
(4) non-competitive inhibition
(5) Covalent modification regulation
Answer: 3
Explanation: When competitive inhibition exists, Vmax does not change and Km increases. For example, malonate is structurally similar to succinate, and malonate is a competitive inhibitor of succinate dehydrogenase.
5. The kinetics of enzymatic reactions are studied
(1) The spatial conformation of the enzyme molecule
(2) the genetic source of the enzyme
(3) the active center of the enzyme
(4) the electrophoretic behavior of the enzyme
(5) Factors that affect the speed of enzymatic reactions
Answer: 5
Explanation: The factors that affect the rate of enzymatic reaction include substrate concentration, enzyme concentration, temperature, pH, inhibitor, and activator. The effect of these six factors on the rate of enzymatic reaction is the kinetics of enzymatic reaction.
6. The statement about competitive inhibition is wrong
(1) A, the structure is similar to the substrate
(2) Binds to the active center of the enzyme
(3) The binding to the enzyme is reversible
(4) The degree of inhibition is only related to the concentration of the inhibitor
(5) Non-covalently bound to enzymes
Answer: 4
Explanation: Inhibitors are similar in structure to substrates, and can compete with the substrate for the active center of the enzyme, preventing the combination of the enzyme and the substrate to form an intermediate product, and inhibiting the activity of the enzyme. Increasing the substrate concentration can weaken the inhibitory effect of competitive inhibitors.
7. Factors that affect the speed of enzymatic reaction do not include
(1) Substrate concentration
(2) the concentration of the enzyme
(3) the pH of the reaction environment
(4) the concentration of zymogen
(5) reaction temperature
Answer: 4
Explanation: Factors affecting the rate of enzymatic reaction include substrate concentration, enzyme concentration, temperature, pH, inhibitor, and activator.
8. The correct concept of Km value is______
(1) The unit of Km value is mol/L
(2) Km value is related to the concentration of enzyme
(3) Km value is small, the affinity of enzyme and substrate is low
(4) The Km values ​​of various isozymes of the same enzyme are the same
(5) is the substrate concentration when the reaction rate is half of the maximum rate
Answer: 5
Explanation: The meaning of Km and Vmax: ①Km is equal to the substrate concentration when the reaction speed is half of the maximum speed. ②Km can represent the affinity of the enzyme and the substrate. The larger the Km value, the lower the affinity of the enzyme to the substrate. ③ Km is the characteristic constant of the enzyme, and the Km value has nothing to do with the concentration of the enzyme. The unit of Km value is mmol/L. ④Vmax is the reaction rate when the enzyme is completely saturated with the substrate, which is proportional to the total concentration of the enzyme. The Km values ​​of various isozymes of the same enzyme are different.
9. After the enzymatic reaction speed reaches Vmax and then increase the substrate concentration, the reason why the reaction speed no longer increases is because
(1) the forward and reverse reactions reach equilibrium
(2) Excess product feedback inhibits enzyme activity
(3) Excess substrate affects the binding of enzyme to substrate
(4) Excess product changes the equilibrium constant of the reaction
(5) the active center of the enzyme has been saturated with the substrate
Answer: 5
Explanation: When the substrate concentration increases to a certain level, the active center of the enzyme is completely saturated, and the reaction speed reaches the maximum. If the substrate concentration is increased, the reaction speed will not be accelerated.
10. Regarding the activation of zymogen and zymogen, which is correct
(1) All enzymes in the body exist in the form of zymogens when they are initially synthesized
(2) Activation of zymogen is a process of covalent modification of enzymes
(3) The activation process of zymogen is the process of complete hydrolysis of the enzyme
(4) The essence of the zymogen activation process is the process of forming or exposing the active center of the enzyme
(5) the activation of zymogen has no meaning
Answer: 4
Explanation: The precursor of an enzyme that is inactive at the time of initial synthesis or secretion is called proenzyme. The process of converting zymogen into active enzyme under certain conditions is called activation of zymogen. The essence of zymogen activation is the formation or exposure of the active center of the enzyme.
11. Which of the descriptions about isozymes is correct?
(1) the molecular structure of the enzyme protein is the same
(2) have the same physical and chemical properties
(3) have the same molecular weight
(4) the catalytic function is the same
(5) have the same immunological properties
Answer: 4
Explanation: Isoenzymes refer to a group of enzymes that catalyze the same chemical reaction but differ in the molecular structure, physicochemical properties and immunological properties of the enzyme protein.
12. The statement about the structure and function of the enzyme molecule is false
(1) Enzymes can be divided into simple proteases and conjugated proteases according to their molecular composition.
(2) Enzymes with the same molecular structure and physicochemical properties are called isozymes because they exist in different tissues or organs
(3) Metal ions and vitamins are the main non-protein components that constitute bound proteases
(4) Genes related to enzyme activity in enzyme molecules are called essential groups
(5) The inactive precursor of an enzyme is called a zymogen, and the inactive zymogen can be converted into an active enzyme after activation
Answer: 2
Explanation: Isoenzymes: refers to a group of enzymes that catalyze the same chemical reaction, but the molecular structure, physicochemical properties, and immunological properties of the enzymes are different.
13. The most common covalent modification of enzymes is___________
(1) Carbonation modification
(2) Sulfation modification
(3) phosphorylation modification
(4) Amino modification
(5) Base modification
Answer: 3
Explanation: Covalent modification regulation of enzymes: the side chain group on the peptide chain of some enzyme proteins can covalently bind or dissociate with a certain chemical group under the catalysis of another enzyme, thereby changing the activity of the enzyme , this way of regulating enzyme activity is called covalent modification of the enzyme. The most common covalent modification of enzymes is phosphorylation modification. Covalent modification of enzymes is another important way of rapid regulation of enzyme activity in vivo.
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