Enzymes

Enzymes MDCAT MCQs with answers

23 past paper MCQs on Enzymes, from the Enzymes unit of MDCAT Biology. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.NAD is an important: (MDCAT 2023)

  1. enzyme
  2. coenzyme
  3. hormone
  4. vitamin
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Correct answer: (b) coenzyme

It is a non-protein carrier of hydrogen that an enzyme needs to work, which is what a coenzyme is.

2.Which enzyme is different from the others? (MDCAT 2023)

  1. pepsin
  2. trypsin
  3. chymotrypsin
  4. lactase
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Correct answer: (d) lactase

The first three digest protein; lactase splits a sugar.

3.Enzymes belong to which class of biomolecules? (UHS MDCAT 2025)

  1. Carbohydrates
  2. Lipids
  3. Proteins
  4. Nucleic acids
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Correct answer: (c) Proteins

Almost every enzyme is a protein; only the ribozymes are not.

4.Select the one which is used by hexokinase as an activator: (NUMS MDCAT 2025)

  1. Cu++
  2. Zn++
  3. Mg++
  4. Fe++
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Correct answer: (c) Mg++

Hexokinase needs magnesium ions to work on ATP.

5.Activated pepsin in which polypeptide fragment is removed is an example of: (NUMS MDCAT 2025)

  1. Apo-enzyme
  2. Holoenzyme
  3. Regulatory enzyme
  4. Non-regulatory enzyme
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Correct answer: (d) Non-regulatory enzyme

Pepsinogen loses a length of its chain once and for all, so the enzyme is not one whose activity is switched up and down.

6.Transfer of phosphate from one compound to the other compound requires an enzyme called: (SIBA MDCAT 2025)

  1. Oxidoreductase
  2. Transferase
  3. Hydrolase
  4. Ligase
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Correct answer: (b) Transferase

An enzyme that moves a group from one molecule to another is a transferase.

7.The covalently bonded non protein part of enzyme is called: - (SIBA MDCAT 2025)

  1. Activator
  2. Prosthetic group
  3. Coenzyme
  4. Apoenzyme
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Correct answer: (b) Prosthetic group

A non-protein part bound to the enzyme by covalent bonds is a prosthetic group.

8.Ribozymes are the biocatalysts that are made up of: (SZABMU MDCAT 2025)

  1. DNA
  2. RNA
  3. Protein
  4. Fatty acid
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Correct answer: (b) RNA

A ribozyme is a length of RNA that acts as a catalyst.

9.What happens to the enzyme after an enzyme-catalysed reaction? (KMU MDCAT 2024)

  1. Reduced to inactive form
  2. Becomes inert
  3. Changes into substrate
  4. Used for another reaction
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Correct answer: (d) Used for another reaction

An enzyme is not used up, so it is free to catalyse the next molecule.

10.An enzyme is capable of acting on a wide range of related substrates. Which of the following is a property of this enzyme? (NUMS MDCAT 2024)

  1. Inflexible active site
  2. Regulatory enzyme
  3. Non-regulatory enzyme
  4. Highly specific enzyme
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Correct answer: (c) Non-regulatory enzyme

A broad specificity belongs to the ordinary non-regulatory enzymes; the regulatory ones are tightly controlled.

11.Zinc ion is attached at the active site of the enzyme carboxypeptidase. The zinc ion functions as (UHS MDCAT 2023)

  1. A coenzyme molecule
  2. An activator
  3. An inhibitor molecule
  4. Controller of Allosteric site
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Correct answer: (b) An activator

A metal ion held at the active site and needed for activity is an activator, or cofactor.

12.Enzyme is a natural substance that: (SZABMU MDCAT 2023)

  1. Increases the rate of chemical reaction
  2. Decreases the rate of chemical reaction
  3. Has no effect on the rate of chemical reaction
  4. Stops the chemical reaction
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Correct answer: (a) Increases the rate of chemical reaction

An enzyme is a biological catalyst; it speeds the reaction up.

13.The major enzymes involved in transfer of phosphate group from ATP to Glucose is: (UHS MDCAT 2023)

  1. Isomerase
  2. Dehydrogenase
  3. Kinase
  4. Decarboxylase
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Correct answer: (c) Kinase

An enzyme that moves a phosphate group from ATP to another molecule is a kinase.

14.An activated enzyme consisting of a polypeptide chain and a cofactor is called? (PMC MDCAT 2022)

  1. Apoenzyme
  2. Holoenzyme
  3. Conjugated enzyme
  4. Hybrid enzyme
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Correct answer: (b) Holoenzyme

Apoenzyme with its cofactor makes the active holoenzyme.

15.All enzymes are composed of: (PMC MDCAT 2022)

  1. Triglycerides
  2. Amino acids
  3. Monosaccharides
  4. Phospholipids
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Correct answer: (b) Amino acids

Enzymes are proteins, and proteins are chains of amino acids.

16.A non-protein chemical compound which is required for enzyme’s catalytic activity is? (PMC MDCAT 2022)

  1. Substrate
  2. Co-factor
  3. DNA
  4. RNA
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Correct answer: (b) Co-factor

A cofactor is the non-protein part an enzyme needs before it will work.

17.Catalysts that increase the rate of biological chemical reaction are called? (PMC MDCAT 2022)

  1. proteins
  2. vitamins
  3. enzymes
  4. minerals
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Correct answer: (c) enzymes

Biological catalysts are enzymes.

18.Inactive enzyme precursors such as pepsinogen for pepsin are called as: (PMC Practice 2021)

  1. Holoenzymes
  2. Actinases
  3. Zymogens
  4. Mucopolysaccharides
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Correct answer: (c) Zymogens

An inactive precursor of an enzyme is a zymogen.

19.An activated enzyme made of polypeptide chain and a cofactor is? (PMC Practice 2021)

  1. Substrate
  2. Coenzyme
  3. Apoenzyme
  4. Holoenzyme
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Correct answer: (d) Holoenzyme

Apoenzyme with its cofactor is the active holoenzyme.

20.A non-protein part which is essential for proper functioning of enzyme is called: (UHS MDCAT 2018)

  1. Additional factor
  2. Cofactor
  3. Efficient co factor
  4. Extra factor
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Correct answer: (b) Cofactor

A non-protein part an enzyme needs is a cofactor.

21.Enzymes have what effect on the end-product? (UHS MDCAT 2017)

  1. They alter the product
  2. The nature of the product is completely changed
  3. No effect
  4. The end product is not obtained
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Correct answer: (c) No effect

A catalyst changes the rate, not the product or the position of equilibrium.

22.An enzyme required Mg2+ to catalyze the substrate. The Mg2+ is best identified as: (UHS MDCAT 2016)

  1. Prosthetic group
  2. Activator
  3. Co-enzyme
  4. Inhibitor
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Correct answer: (b) Activator

A metal ion needed for activity is an activator, or cofactor.

23.Some enzymes require helper which is non-protein part for its efficient functioning that is called: (UHS MDCAT 2015)

  1. Accelerator
  2. Cofactor
  3. Prosthetic group
  4. Apoenzyme
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Correct answer: (b) Cofactor

A non-protein part an enzyme needs is a cofactor.

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