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1. What are Enzymes?
Enzymes are substances that act as a catalyst in various chemical and biochemical
reactions occurring inside our body. Enzymes are generally categorized as proteins, the
only exception to this generalisation is the presence of catalytic RNA. Enzymes works or
catalyse a biochemical reaction by lowering the activation energy barrier of the reaction.
It is important to understand that enzymes do not change the chemical equilibrium of the
reaction and is not consumed during the process. Enzymes work by adhering to reactant
molecules and maintaining them in a position that allows chemical bond-breaking and
bond-forming to occur more easily. The article provides MCQs on enzymes for a
comprehensive understanding of the topic. These questions will help students in the
preparation of various competitive examinations.
Multiple Choice questions on Enzymes
Since we have revised the basic details of the enzymes, let us look into the MCQs of
enzymes which are specifically aimed to develop a precise understanding of the concept.
1. The general mechanism is that an enzyme acts by:
A. Reducing the activation energy
B. Increasing activation energy
C. Decreasing pH value
D. Increasing the pH value
Answer: Reducing the activation energy
Explanation: Enzymes catalyse the biochemical reactions by participating as a catalyst
they are simply responsible for increasing the rate of reaction. Enzymes catalyse a
reaction by binding substrate to the active site and various non-covalent interactions are
formed and broken which provides energy. This energy from bond formation and
breakage counteracts the activation barrier thus lowering the activation energy.
2. The coenzyme is:
A. Often a metal
B. always a protein
C. often a vitamin
D. always an inorganic compound
Answer: Often a vitamin
Explanation: Coenzymes are chemical molecules that are required for catalytic activity
by numerous enzymes. Vitamins or vitamin compounds are often used. In the absence of
enzymes, they can operate as catalysts, although not as effective as when used in

2. combination with an enzyme. 5-Deoxyadenosylcobalamin (coenzyme B12), flavin
adenine dinucleotide, and lipoate are examples of common coenzymes.
3. An enzyme that joins the ends of two strands of nucleic acid is:
A. Polymerase
B. ligase
C. synthetase
D. Helicase
Answer: Ligase
Explanation: DNA ligase is the enzyme responsible for the formation of the
phosphodiester bond between nucleotide base pairs. This enzyme plays an important role
in the DNA damage repair pathways.
4. Which of the following is produced with the combination of apoenzyme and
coenzyme:
A. Holoenzyme
B. Enzyme substrate complex
C. Prosthetic group
D. Enzyme product complex
Answer: Holoenzyme
Explanation: Holoenzymes are catalytically active enzymes that are coupled with
cofactor or prosthetic groups, according to the definition of biochemistry. The
apoenzyme is the protein portion of the enzyme that does not include the prosthetic
group.
5. Which one among them is the example of competitive inhibition of an enzyme:
A. Succinic dehydrogenase by malonic acid
B. Cytochrome oxidase by cyanide
C. Hexokinase by glucose-6-phosphate
D. Carbonic anhydrase by carbon dioxide
Answer: Succinic dehydrogenase by malonic acid
Explanation: The inhibition of succinic dehydrogenase by malonic acid is an example
of the competitive inhibition of an enzyme. A competitive inhibitor looks like the
substrate and binds to the enzyme's active site. The substrate is then barred from binding
to the same active site as the enzyme. Malonate is a competitive inhibitor of succinate
dehydrogenase: it binds to the enzyme's active sites without reacting, and therefore
competes with succinate, the enzyme's regular substrate.

3. 6. Blocking of enzyme action by blocking its active site is called as:
A. Allosteric inhibition
B. Feedback inhibition
C. Competitive inhibition
D. Non-competitive inhibition
Answer: Competitive inhibition
Explanation: Competitive inhibitors are structural analogues of the substrate and hence
compete for the same active binding sites on the enzyme as the substrate. Because of this
rivalry, the impact of the competitive inhibitor can be overcome if enough substrate is
given, i.e., the substrate will eventually fill all binding sites.
7. Diastase takes part in digestion of which one:
A. Protein
B. Starch
C. Amino acids
D. Fat
Answer: Starch
Explanation: Any of set of enzymes that catalyse the breakdown of starch into maltose
is known as diastase. Urine diastase is effective in detecting ambiguous abdominal
situations, particularly when pancreatitis, stones in the common bile duct, jaundice, and
ruling out postoperative pancreatic damage are suspected; provided the diastase level is
associated with clinical symptoms of the patient.
8. Enzyme catalysing rearrangement of atomic grouping without altering molecular
weight or number of atom is:
A. Ligase
B. Isomerase
C. Oxidoreductase
D. Hydrolase
Answer: Isomerase
Explanation: Isomerases are enzymes that aid in the conversion of a chemical substance
from one isomeric form to another by catalysing isomerization modifications in a
molecule. Isomerization is the process of converting one isomer into another. Any of two
or more versions of a molecule having the same chemical formula but a distinct
stereochemical arrangement of the atoms is referred to as an isomer.

4. 9. Enzyme complex involved in alcoholic fermentation is:
A. Zymase
B. Invertase
C. Lipase
D. Amylase
Answer: Zymase
Explanation: Zymase is a complex of enzymes that catalyses the conversion of sugar to
ethanol and carbon dioxide. It's found in yeasts naturally. The activity of zymase differs
amongst yeast strains.
10. Zymogen or proenzyme is a :
A. Modulator
B. Vitamin
C. Enzyme precursor
D. Hormone
Answer: Enzyme precursor
Explanation: Enzyme precursors are the inactive form of the enzymes which are
generally activated by action of another enzyme or chemical compounds, the activation
of such enzymes are highly regulated by the cell signalling pathways.
11. Enzymes are made Up of:
A. Fats
B. Proteins
C. Nucleic acids
D. Vitamins
Answer: Proteins
Explanation: The enzymes are the tertiary and quaternary structures of the protein, the
only exception to it is the presence of the catalytic RNA molecules.
12. Enzymes are polymers of:
A. Hexose sugar
B. Amino acids
C. Fatty acids
D. Inorganic phosphate
Answer: Amino acid

5. Explanation: Enzymes are mostly proteins, proteins are defined as the polymers of
amino acids thus enzymes can be defined as the polymer of the amino acids.
13. The enzyme which hydrolyses starch to maltose is:
A. Protease
B. Amylase
C. Lactase
D. Maltase
Answer: Amylase
Explanation: Amylases are a family of starch-hydrolyzing enzymes. Many enzymes
work with starch or oligosaccharides made from it. Hydrolases such as -amylase, -
amylase, glucoamylase, -glucosidase, debranching enzymes, and transferases such as
CGTase, 4--glucanotransferase, and a branching enzyme are among the 19 enzymes
recognised as belonging to the microbial amylase group.
14. This enzyme was first isolated and purified in the form of crystals:
A. Urease
B. pepsin
C. Amylase
D. Ribonuclease
Answer: Urease
Explanation: Urease is a cytosolic enzyme that catalyses the conversion of urea to
ammonia and CO2. Ureases are members of the amidohydrolases and phosphotriesterases
superfamily. Ureases may be found in a wide variety of bacteria, fungi, algae, plants, and
animals, as well as in soils as a soil enzyme. They are high-molecular-weight nickel-
containing metalloenzymes.
15. This statement about enzymes is true:
A. Enzymes accelerate reactions by lowering the 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: All of these
Explanation: Enzymes catalyze the biochemical reaction, they increase the rate of
reaction by lowering the activation barrier. They are generally tertiary and quaternary
proteins, they are not consumed in the reaction.

6. 16. Koshland proposed which model:
A. Fluid mosaic model
B. Induced fit model
C. Lock and key model
D. Reflective index model
Answer: Induced fit model
Explanation: The induced fit model is a model for the interaction of enzymes and
substrates. It states that only the appropriate substrate may cause the active site to align
properly, allowing the enzyme to fulfil its catalytic job. It also implies that the active site
changes until it is entirely attached to the substrate, at which time the final shape and
charge are decided.
17. In the human body optimum temperature for enzymatic activities is:
A. 37-degree celsius
B. 25-degree celsius
C. 20-degree celsius
D. 15-degree celsius
Answer: 37 degrees celsius
Explanation: Enzymes are temperature sensitive, they tend to denature in high
temperatures, the optimal temperature for the enzymes in the human body is around 37
degrees celsius.
18. Optimum pH value of pepsin is:
A. 1.4
B. 2
C. 3.5
D. 5
Answer: 1.4
Explanation: pH plays an important role in enzyme activity, enzymes are often active
only in a narrow pH range. Pepsin gets denatured in pH lower and higher than the pH
range of 1.4 to 1.6. The optimal pH for pepsin activity is 1.4.
19. The enzyme minus its coenzyme known as:
A. Apoenzyme
B. Metalloenzyme
C. Isoenzyme
D. All of these

7. Answer: Apoenzyme
Explanation: The apoenzyme is the protein part of the holoenzyme. Apoenzymes and
prosthetic groups combinely to form the holoenzymes.
20. Which of the following is the non-protein component of the enzyme?
A. Cofactor
B. Activator
C. Coenzyme
D. All of these
Answer: All of these
Explanation: Cofactor and coenzymes are the parts of the holoenzyme. Holoenzyme is
the catalytic complex that contains both the protein part of an enzyme known as
apoprotein and the metal-organic and organic compounds, that is cofactor and
coenzymes.
21. An uncatalyzed reaction involved:
A. High activation energy
B. Low activation energy
C. Balanced activation energy
D. All of these
Answer: High activation energy
Explanation: The high activation energy required for the catalysis of the biochemical
reaction is a major barrier of the uncatalyzed reaction in the cells.
22. Which among them is not attribute of enzymes:
A. Specific in nature
B. Protein in chemistry
C. Consumed in reaction
D. Increased rate of reaction
Answer: Consumed in reaction
Explanation: The enzymes only lower the activation barrier of the biochemical reaction,
they do not change the equilibrium, the enzyme also does not get consumed in the
reaction.
23. Zn+2
is an inorganic activator for enzymes:
A. Carbonic anhydrase
B. Phosphatase

8. C. Chymotrypsin
D. Maltase
Answer: Chymotrypsin
Explanation: The zinc cation is a cofactor of the enzyme chymotrypsin it is required for
enzyme catalysis.
24. Mg+2
is an inorganic activator for enzymes:
A. Phosphatase
B. Carbonic anhydrase
C. Amylase
D. Enterokinase
Answer: Phosphatase
Explanation: Mg ions (cation) acts as cofactor of the enzyme phosphatase that is
required for the enzyme activity.
25. Which among them is a cofactor:
A. Inorganic ion
B. Organic molecule
C. Both A and B
D. None of these
Answer: Both A and B
Explanation: A cofactor is an apoprotein that has a metal ion or one or more inorganic
ions linked to it. Mg2+
, Fe2+
, Zn2+
, and Mn2+
are examples of common cofactors. Metallic
cofactors are used by enzyme examples including Cytochrome oxidase, catalase,
peroxidase, pyruvate kinase, hexokinase, and glucose 6-phosphatase.
In conclusion of the article, we have discussed multiple questions that will help in
understanding the enzyme