Enzymes MCQs

By: Prof. Dr. Fazal Rehman | Last updated: February 3, 2024

Set of Important MCQs on Enzymes for the preparation of tests for chemistry and biology. 

Aldolase belongs to ________ class of enzymes.

  1. Transferases
  2. Lyases
  3. Hydrolases
  4. Isomerases

Question’s Answer: Lyases

All of the following enzymes show group specificity, excluding

  1. Hexokinase
  2. Glucokinase
  3. Phospholipase
  4. Amino acid oxidase

Question’s Answer: Glucokinase

Pyruvate carboxylase belongs to  ________  class of enzymes.

  1. Ligase
  2. Oxidoreductasec
  3. Transferase
  4. Hydrolase

Question’s Answer: Ligase

The co-enzymes have which properties?

  1. Having the same quaternary structures like the enzymes
  2. Structural analogues of enzymes
  3. Soluble, colloidal, protein molecules
  4. Heat stable, dialyzable, non-protein organic molecules

Question’s Answer: Heat stable, dialyzable, non-protein organic molecules

When substrate concentration is equal to Km of an enzyme:

  1. Half of the enzyme molecules are bound to the substrate
  2. The velocity of the reaction is = V
  3. The enzyme is saturated with the substrate
  4. The reaction velocity becomes independent of substrate concentration

Question’s Answer: Half of the enzyme molecules are bound to the substrate

A sigmoidal plot of substrate concentration ([S]) versus reaction velocity (V) may indicate.

  1. Michaelis-Menten kinetics
  2. Non-competitive inhibition
  3. Competitive inhibition
  4. Co-operative binding

Question’s Answer: Co-operative binding

An inducer is not needed in which type of enzyme?

  1. Allosteric enzyme
  2. Inducible enzyme
  3. Constitutive enzyme
  4. An isoenzyme

Question’s Answer: Constitutive enzyme

The V of an enzyme represents which of the following?

  1. Substrate concentration
  2. The amount of active enzyme
  3. Half the substrate
  4. The total concentration of the enzymes

Question’s Answer: The amount of active enzyme

Which is characteristic of a competitive inhibitor?

  1. It may be a feedback inhibitor
  2. It decreases the Vmax of the enzyme
  3. It interferes with the binding of the substrate to the active site
  4. It causes irreversible inhibition

Question’s Answer: It interferes with the binding of the substrate to the active site

Enzymes, which are produced inactive form in the living cells, in are called

  1. Proenzymes
  2. Apoenzymes
  3. Lysozymes
  4. Ribozymes

Question’s Answer: Proenzymes

Which is a proenzyme?

  1. angiotensin converting enzyme
  2. Pepsinogen
  4. None of these

Question’s Answer: Pepsinogen

The enzyme _______  that adds water across a double bond or removes water to create a double bond without breaking the bonds?

  1. Hydrolase
  2. Hydroxylase
  3. Hydratase
  4. Esterase

Question’s Answer: Hydratase

Effect of raising the temperature for 20- 80°C on enzyme activity would be.

  1. Increasing velocity
  2. Decreasing velocity
  3. Increasing followed by decreasing velocity
  4. Both A, B and C

Question’s Answer: Increasing followed by decreasing velocity

Cytochrome P-450 carries which type of enzyme?

  1. Monoamine oxidase
  2. Catalase
  3. Dehydrogenase
  4. Monooxygenase

Question’s Answer: Monooxygenase

What is the most ideal statement regarding Active Site’ of an enzyme

  1. Nearly all polypeptide chains must participate in catalysis
  2. Most of the amino acids involved in Active Site are located near each other on the polypeptide
  3. Conformation of the Active Site does not exist until the substrate binds
  4. Amino acids forming Active Site are in close proximity due to specific orientation in space

Question’s Answer: Amino acids forming Active Site are in close proximity due to specific orientation in space

Which of the following is an example of multifunctional enzyme?

  1. Acetyl-CoA carboxylase
  2. Pyruvate dehydrogenase complex
  3. Animal fatty acid synthase
  4. None of these

Question’s Answer: Animal fatty acid synthase

An enzyme that converts an aldose sugar to a keto-sugar is classified as ______.

  1. Transferase
  2. Oxidoreductase
  3. Isomerase
  4. Hydrolase

Question’s Answer: Isomerase

If the initial velocity of an enzymatic reaction is equal to Vmax, the substrate concentration is

  1. Far above KM
  2. Equal to KM
  3. Half of K
  4. Both A, B and C

Question’s Answer: Far above KM

During competitive inhibition, the inhibitor

  1. Competes with the substrate
  2. Irreversibly binds with the enzyme
  3. Competes with the enzyme
  4. Both A, B and C

Question’s Answer: Competes with the substrate

Competitive inhibitors ______.

  1. Decrease the VMAX
  2. Decrease the KM of the enzyme for the substrate
  3. Increase the VMAX
  4. Increase the KM of the enzyme for the substrate

Question’s Answer: Increase the KM of the enzyme for the substrate

Which is a therapeutic enzyme?

  1. Glucose-6-P dehydrogenase
  2. Streptokinase
  3. Monoamine oxidase
  4. Allopurinol

Question’s Answer: Streptokinase

The role of co-enzyme in the enzymatic reactions is

  1. Enhancing the specificity
  2. Increasing the number of binding sites on the Apo-enzyme.
  3. Acting as an acceptor for intermediate products of the substrate
  4. None of these

Question’s Answer: Acting as an acceptor for intermediate products of the substrate

Which is not true regarding enzymes?

  1. They remain active even after separation form the source
  2. They are destroyed after completion of the reaction
  3. They are destroyed at high temperatures
  4. Their activity depends upon the pH of the solution

Question’s Answer: They are destroyed after completion of the reaction

Michalis constant (Km) of an enzyme is ______ .

  1. Dependent upon the enzyme concentration.
  2. Numerically equal to substrate concentration at VMAX
  3. Numerically equal VMAX
  4. Independent of pH

Question’s Answer: Numerically equal to substrate concentration at VMAX

During the estimation of enzyme activity, all of the following are kept constant, excluding

  1. Enzyme concentration
  2. pH
  3. Substrate concentration
  4. Temperature

Question’s Answer: Enzyme concentration

As per Michalis-Menten equation, at a very low substrate concentration, the initial velocity of the enzymatic reaction is_________.

  1. Not affected by enzyme concentration
  2. Nearly equal to Vmax
  3. Inversely proportional to substrate concentration
  4. Directly proportional to substrate concentration

Question’s Answer: Directly proportional to substrate concentration

The isoenzymes differ from each other in all of the following, excluding

  1. Michaelis-Menten constant
  2. Specific inhibitors
  3. Amino acid sequence
  4. Catalytic activity

Question’s Answer: Catalytic activity

What is Lock and Key Theory?

  1. The active site is flexible and adjusts to the substrate
  2. The structure of the substrate is identical to the active site
  3. The Enzyme-Substrate complex has higher energy than free substrate and enzyme
  4. The active site is complementary to the shape of the substrate

Question’s Answer: The active site is complementary to the shape of the substrate

Which  was the first enzyme to be isolated, purified and crystallized?

  1. Chymotrypsin
  2. Urease
  3. Lysozyme
  4. Ribonuclease

Question’s Answer: Urease

The concept of “Induced Fit as a theory implies which of the following?

  1. The template theory adequately explains the enzyme mechanism
  2. The catalytic groups are brought into proper alignment by the substrate
  3. The conformation of the substrate changes upon binding with the enzyme
  4. Formation of ES complex is always the fastest step

Question’s Answer: The catalytic groups are brought into proper alignment by the substrate

The alloenzymes are

  1. Chemically and immunologically different forms of the enzymes
  2. The same enzyme isolated from different tissues or subcellular compartments
  3. Structurally related enzyme that carry out different reactions
  4. Chemically identical enzymes isolated from different species

Question’s Answer: Chemically identical enzymes isolated from different species

Amil Fischer’s Lock-and-key’ theory for enzymes was supported by the fact-

  1. Size of the active site is very small comared to the total protein
  2. Co-enzymes act as the ‘key’ at the active site
  3. Substances similar in structure to that of substrate inhibit enzyme reactions
  4. The enzyme adapts after binding with the substrate and locks it at the active site

Question’s Answer: Substances similar in structure to that of substrate inhibit enzyme reactions

All _________  enzymes carry Flavin nucleotides as prosthetic group.

  1. L-Amino acid oxidase
  2. Xanthine oxidase
  3. Cytochrome oxidase
  4. None of these

Question’s Answer: Cytochrome oxidase

Which type of enzyme can supply the citric acid cycle with oxaloacetate from pyruvate?

  1. A ligase
  2. A mutase
  3. An isomerase.
  4. Both A, B and C

Question’s Answer: A ligase

Cooperativity of an allosteric enzyme can be studied by-

  1. Michalis-Menten equation
  2. Hill Equation
  3. Line weaver-Burk plot
  4. Both A, B and C

Question’s Answer: Hill Equation

In-vivo of an enzymatic reaction can be controlled by:

  1. Interconversion b/n forms with different Km values
  2. Phosphorylation
  3. Proteolytic.cleavage of the polypeptides
  4. Both A, B and C

Question’s Answer: Both A, B and C

Which is a co-enzyme?

  1. Vitamin
  2. ATP
  3. Ubiquinone
  4. Both A, B and C

Question’s Answer: Both A, B and C

Hydrolysis of proteins by protease enzymes would yield amino acids in the form of which of the following?

  1. Racemic mixture of amino acids
  2. D-Amino acids
  3. D. L-Amino acids
  4. L-Amino acids.

Question’s Answer: L-Amino acids

A number of biochemical assays are linked with enzymatic conversion of NAD NADH. The reaction velocity in these assays is determined by measuring the change in optical density

  1. 550 nm
  2. 340 nm
  3. 290 nm
  4. 210 nm

Question’s Answer: 340 nm

The Vmax of an enzymatic reaction may be dependent on which of the following?

  1. K of the enzyme
  2. Concentration of the enzyme
  3. Concentration of the competitive inhibitor
  4. Both A, B and C

Question’s Answer: Concentration of the enzyme

Which is a hydrogen transferring co-enzyme?

  1. Pyridoxal phosphate
  2. Thiamine pyrophosphate
  3. NADP+
  4. ATP

Question’s Answer: NADP+

According to Steady state kinetics,Which statements is false?

  1. When [S] =KM, half the substrate binding sites are saturated
  2. KM is larger than the dissociation constants for [ES]
  3. Excluding at very low [S], increase in V₁ is less than increase in [S]
  4. V equals [ES] times k3

Question’s Answer: KM is larger than the dissociation constants for [ES]

Mostly the regulatory reactions in a pathway are enzyme limited, Which is true about such reactions

  1. They are rate limiting
  2. They are exergonic and
  3. They are far from equilibrium irreversible
  4. Both A, B and C

Question’s Answer: Both A, B and C

The enzymes ______ are always present in a cell/organism at relatively constant concentrations.

  1. Proenzymes
  2. Constitutive enzymes
  3. Functional enzymes
  4. Facultative enzymes

Question’s Answer: Proenzymes

Which among the following is extracellular?

  1. Glucose-6-Phosphatase
  2. Hexokinase
  3. Pancreatic amylase
  4. Citrate Synthase

Question’s Answer: Pancreatic amylase

Choose the most ideal statement regarding Allosteric enzymes

  1. Often found at the first committed step
  2. Subject to regulation by covalent modification
  3. They are usually multi-subunit systems
  4. Both A, B and C

Question’s Answer: Both A, B and C

The isoenzymes are

  1. Chemically and immunologically different forms of the enzymes
  2. Chemically and immunologically identical forms of the different enzymes
  3. Different enzymes that carry out same reactions
  4. Structurally related enzymes that carry out different reactions

Question’s Answer: Chemically and immunologically different forms of the enzymes

Which enzymes catalyze the binding of two substrates by covalent bonds?

  1. Lyases
  2. Ligases
  3. Synthases
  4. Reductases

Question’s Answer: Ligases

Who proposed the induced fit model of enzyme action?

  1. Amil Fischer
  2. Peter Mitchel
  3. Daniel Koshland
  4. Robert Gilbert

Question’s Answer: Daniel Koshland

In lineweaver-Burk plot, the Y-intercept represents

  1. Vmax
  2. 1/Vmax
  3. 1/Km
  4. Km/Vmax

Question’s Answer: 1/Vmax

Which statements regarding enzyme kinetics is NOT TRUE?

  1. Value of Km is independent concentration
  2. Low signifies high affinity for the substrate (s)
  3. The V is reached when [ES] concentration is maximal
  4. Enzymes increase the rate of the reaction by enhancing the forward reaction

Question’s Answer: Enzymes increase the rate of the reaction by enhancing the forward reaction

Which is NOT TRUE regarding enzymes

  1. They lower the activation energy of the reaction
  2. They change the rate of approach to equilibrium
  3. They can be very selective with respect to substrate
  4. They lower the standard free energy of the reaction

Question’s Answer: They lower the standard free energy of the reaction

Which is not a characteristics of allosteric enzymes?

  1. Feedback inhibition
  2. Greater specificity than non- allosteric enzymes
  3. They can be very selective with respect to substrate-
  4. They lower the standard free energy of the reaction

Question’s Answer: Greater specificity than non-allosteric enzymes

Important Questions about Enzymes

  1. Enzymes MCQs
  2. Inhibition in enzymes
  3. Which enzyme digests starch?
  4. Which enzyme digests protein?
  5. which enzyme is present in saliva?
  6. Which enzyme is not present in succus entericus?
  7. Which enzyme breaks down protein in the stomach?
  8. Which enzyme converts fibrinogen to fibrin?
  9. Which enzyme converts glucose into alcohol?
  10. Which enzyme digests fat?
  11. Which enzyme digests milk protein?
  12. Which enzyme is used in PCR?
  13. Which enzyme unzips the DNA double helix?
  14. Which liver enzyme increases with alcohol?
  15. Which enzyme cuts DNA?
  16. Which enzyme catalyzes the first step of glycolysis?
  17. Which enzyme binds DNA fragments together?
  18. Which enzyme transcribes DNA into RNA?
  19. which enzyme adds new nucleotides?
  20. Which enzyme digests cellulose?
  21. Which enzyme separates the two strands of DNA?
  22. Which enzyme converts carbohydrates into glucose?
  23. Which enzyme removes RNA primer?
  24. Which enzymes help in digestion?
  25. Which enzyme works best in acidic conditions?
  26. Which enzyme synthesizes tRNA?
  27. Which enzyme secreted by pancreas?
  28. Which enzyme converts maltose into glucose?
  29. Which vitamins work as coenzyme?

More Biochemistry MCQs

  1. Acid and Base MCQs
  2. Carbohydrate MCQs
  3. Proteins MCQs
  4. Lipids and Biomembranes MCQs
  5. Nucleic acids MCQs
  6. Metabolism of Carbohydrates MCQs
  7. Enzymes MCQs
  8. Vitamins and Hormones MCQs
  9. Bioenergetic MCQs
  10. Biotechnology MCQs
  11. Biotechnology MCQs 2
  12. Basic Biochemistry MCQs (important)
  13. CHEMISTRY MCQs From all subjects of  Chemistry

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