Enzymes

Enzymes MDCAT MCQs with answers

110 past paper MCQs from Biology unit 6, Enzymes, across 4 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Enzymes

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.

All 23 Enzymes MCQs → Enzymes notes →

Mode of Enzyme Action

4.Enzymes lower the energy of the transition state of a metabolic reaction by: (MDCAT 2022)

  1. changing the substrate into a product directly
  2. distorting the molecules bound in the active site
  3. binding the fatty acids in the active site
  4. raising the temperature of the medium
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Correct answer: (b) distorting the molecules bound in the active site

Strain put on the bound substrate brings it closer to the transition state, so less activation energy is needed.

5.The active sites of enzymes are composed of: (MDCAT 2023)

  1. a few nucleotides
  2. a few nucleosides
  3. a few saccharides
  4. a few amino acids
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Correct answer: (d) a few amino acids

A handful of amino acid side chains, brought together by the folding of the chain, make the active site.

6.The induced fit model of enzyme activity suggests that an enzyme: (MDCAT 2024)

  1. cannot modify its active site
  2. can bind to a single substrate
  3. can catalyze related reactions
  4. usually belongs to the non-regulatory enzymes
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Correct answer: (c) can catalyze related reactions

The active site is flexible and moulds itself around the substrate, so related substrates can be accepted.

All 31 Mode of Enzyme Action MCQs → Mode of Enzyme Action notes →

Factors Affecting the Rate of Enzyme Reactions

7.What is the best physiological pH for the working of most of the cellular enzymes of humans? (MDCAT 2022)

  1. 2-3
  2. 3-5
  3. 6-8
  4. 8-10
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Correct answer: (c) 6-8

Most enzymes inside the cell work near neutrality; pepsin in the stomach is the well-known exception.

8.Which enzyme can work at pH 7 of the medium? (MDCAT 2023)

  1. pepsin
  2. sucrase
  3. chymotrypsin
  4. pancreatic lipase
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Correct answer: (b) sucrase

Sucrase works near neutrality; pepsin needs a strong acid and the pancreatic enzymes an alkaline medium.

9.Which of the following statements is incorrect regarding the rate of enzymatic action? (MDCAT 2024)

  1. an increase in enzyme concentration increases the rate
  2. an increase in enzyme concentration reduces the rate
  3. all enzymes work at their maximum rate at their optimum temperature
  4. all enzymes work at their maximum rate at their optimum pH
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Correct answer: (b) an increase in enzyme concentration reduces the rate

More enzyme means more active sites, so with substrate to spare the rate rises rather than falls.

All 26 Factors Affecting the Rate of Enzyme Reactions MCQs → Factors Affecting the Rate of Enzyme Reactions notes →

Inhibitors

10.Competitive inhibitors compete with the: (MDCAT 2022)

  1. substrate
  2. enzyme
  3. product
  4. coenzyme
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Correct answer: (a) substrate

They resemble the substrate and take its place in the active site.

11.Competitive inhibitors are: (MDCAT 2023)

  1. homologous to the substrate
  2. analogous to the substrate
  3. smaller than the substrate
  4. larger than the substrate
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Correct answer: (b) analogous to the substrate

They resemble the substrate closely enough in shape to occupy its active site.

12.Reversible inhibitors differ from Irreversible Inhibitors because they: (UHS MDCAT 2025)

  1. Binds permanently and cannot be removed
  2. Bind temporarily and can be removed
  3. Permanently inactivate the enzyme
  4. Change enzyme structure permanently
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Correct answer: (b) Bind temporarily and can be removed

A reversible inhibitor is held by weak bonds and lets go, so the enzyme recovers.

All 30 Inhibitors MCQs → Inhibitors notes →

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