Mode of Enzyme Action

Mode of Enzyme Action MDCAT MCQs with answers

31 past paper MCQs on Mode of Enzyme Action, 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.

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1.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.

2.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.

3.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.

4.According to Lock and Key model, the active site is regarded as: (UHS MDCAT 2025)

  1. Rigid and specific
  2. Flexible and specific
  3. Rigid and non specific
  4. Flexible and non specific
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Correct answer: (a) Rigid and specific

The lock and key model treats the active site as a rigid shape that only its own substrate fits.

5.The active site is important in enzyme action because: (KMU MDCAT 2025)

  1. It binds to the substrate
  2. It maintains the pH of reaction
  3. It provides energy for reaction
  4. It changes the shape of the enzyme
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Correct answer: (a) It binds to the substrate

The active site is the pocket the substrate fits into, where the reaction is catalysed.

6.Enzymes increase the rate of reaction by: (KMU MDCAT 2025)

  1. Increasing activation energy
  2. Lowering activation energy
  3. Increasing pH
  4. Decreasing pH
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Correct answer: (b) Lowering activation energy

An enzyme offers a path of lower activation energy, so more collisions succeed.

7.Induced fit model of enzyme activity suggests that an enzyme: (NUMS MDCAT 2025)

  1. Cannot modify its active sites
  2. Can bind to a single substrate
  3. Can catalyze related specific reaction
  4. Usually belongs to non-regulatory enzyme
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Correct answer: (c) Can catalyze related specific reaction

The active site is moulded around the substrate as it binds, so an enzyme can serve a group of related reactions.

8.The linkage between substrate molecule and active site is: (NUMS MDCAT 2025)

  1. Ionic bonding
  2. Disulfide bonding
  3. Hydrogen bonding
  4. Covalent bonding
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Correct answer: (c) Hydrogen bonding

The substrate is held in the active site by weak bonds, chiefly hydrogen bonds, so it can be released again.

9.The induced fit model differs from the Lock and Key model because the enzyme in this model: (SZABMU MDCAT 2025)

  1. Has a rigid and fixed active site
  2. Changes shape to fit the substrate
  3. Is non-specific in its action
  4. Is denatured during reaction
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Correct answer: (b) Changes shape to fit the substrate

In the induced fit model the active site is moulded around the substrate as it binds.

10.The enzymes enable the conversion of substrates into products by (KMU MDCAT 2024)

  1. Changing equilibrium in the direction of the substrate
  2. Increasing the activation energy
  3. Increasing the substrate concentration
  4. Lowering the activation energy
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Correct answer: (d) Lowering the activation energy

An enzyme offers a path over a lower energy barrier; it does not shift the equilibrium.

11.Enzymes lower the activation energy by stabilizing the transition state of a metabolic reaction due to? (UHS MDCAT 2023)

  1. Changing conditions within the active site
  2. Changing conditions within the protein framework
  3. Rearranging the fatty acids in active site
  4. Distorting the molecules in the allosteric site
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Correct answer: (a) Changing conditions within the active site

The chemical surroundings inside the active site hold the transition state and lower the barrier to it.

12.The catalytic activity of an enzyme is restricted to its small portion: (SZABMU MDCAT 2023)

  1. Active site
  2. Passive site
  3. Allosteric site
  4. Regulation site
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Correct answer: (a) Active site

Only the active site, a small pocket in the molecule, does the catalysis.

13.Enzyme work by lowering the of the reaction they catalyze: (SZABMU MDCAT 2023)

  1. Kinetic energy
  2. Activation energy
  3. Heat energy
  4. Potential energy
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Correct answer: (b) Activation energy

An enzyme offers a path over a lower energy barrier, so more collisions succeed.

14.Catalytic activity of an enzyme is restricted to its: (PMC MDCAT 2022)

  1. Active site
  2. Catalytic site
  3. Binding site
  4. Allosteric site
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Correct answer: (a) Active site

Only the active site catalyses; the rest of the molecule holds it in shape.

15.The energy required in order to start a reaction is (PMC MDCAT 2022)

  1. Startup energy
  2. Initial energy
  3. point energy
  4. Activation energy
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Correct answer: (d) Activation energy

That least energy is the activation energy.

16.What does the active site of the enzyme do? (PMC MDCAT 2022)

  1. Looks like a lump projection from the surface of an enzyme
  2. Forms no chemical bond with substrate
  3. Never changes
  4. The specificity of an enzyme is determined by its structure
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Correct answer: (d) The specificity of an enzyme is determined by its structure

The shape of the active site is what decides which substrate will fit it.

17.An enzyme can: (PMC MDCAT 2022)

  1. Maintain the biochemical reaction
  2. Decrease the biochemical reaction
  3. Lower the need of activation energy
  4. Be the substitute of activation energy
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Correct answer: (c) Lower the need of activation energy

An enzyme offers a path over a lower energy barrier.

18.What is correct about the active site of the enzyme? (PMC MDCAT 2022)

  1. it detaches itself from the product after catalysis
  2. It's shape is complementary to the substrate
  3. It Is Involved in feedback inhibition
  4. It Is Involved In irreversible, non-competitive Inhibition
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Correct answer: (b) It's shape is complementary to the substrate

The active site is shaped to fit its own substrate and no other.

19.Which of the following part of enzyme recognize the substrate? (PMC MDCAT 2022)

  1. Binding site
  2. Active site
  3. Catalytic site
  4. Overall structure of an enzyme
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Correct answer: (a) Binding site

The binding site of the active site is what the substrate is held by.

20.The enzyme substrate complex is formed in which part of the enzyme molecule? (PMC MDCAT 2022)

  1. Binding site
  2. Allosteric site
  3. Catalytic site
  4. On all over the surface of enzyme
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Correct answer: (a) Binding site

The substrate is held at the binding site of the active site while it is worked on.

21.Which type of bonds are never formed when a substrate fits into the active site of an enzyme? (PMC Practice 2021)

  1. Hydrogen bonds
  2. Ionic interactions
  3. Hydrophobic interactions
  4. Covalent linkages
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Correct answer: (d) Covalent linkages

The substrate is held by weak bonds so that it can be released again; a covalent link would trap it.

22.In 1959, Koshland proposed which of the following? (PMC Practice 2021)

  1. Unit membrane model
  2. Fluid mosaic model
  3. Reflective index model
  4. Induced fit model
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Correct answer: (d) Induced fit model

Koshland’s induced fit model has the active site moulded round the substrate as it binds.

23.The substance that is attached to the enzyme at specific place and converted into product is called as? (PMC Practice 2021)

  1. Co-factor
  2. Iso-zyme
  3. Active site
  4. Substrate
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Correct answer: (d) Substrate

The molecule the enzyme acts upon is the substrate.

24.Enzymes work by which of the following? (PMC Practice 2021)

  1. Increasing the activation energy
  2. Reducing the activation energy
  3. Making exergonic reactions endergonic
  4. Making endergonic reactions exergonic
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Correct answer: (b) Reducing the activation energy

An enzyme offers a path over a lower energy barrier.

25.The number of substrate molecules converted into the product by one molecule of enzyme active site per unit time is called? (PMC Practice 2021)

  1. Turnover number
  2. Substrate number
  3. Reaction number
  4. None of these options is correct
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Correct answer: (a) Turnover number

That number is the turnover number of the enzyme.

26.Enzymes work by lowering the ______ of the reactions they catalyse: (PMC MDCAT 2020)

  1. Kinetic energy
  2. Activation energy
  3. Heat energy
  4. Potential energy
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Correct answer: (b) Activation energy

An enzyme offers a path over a lower energy barrier.

27.Lock and Key Model for enzyme action propose by Emil Fischer suggests that: (PMC MDCAT 2020)

  1. Enzymes are unbiased for the substrate
  2. Enzymes can modify their active sites
  3. Enzymes are restricted to one reaction type
  4. An enzyme can catalyze variety of reactions
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Correct answer: (c) Enzymes are restricted to one reaction type

The lock and key model treats the active site as a rigid shape that only its own substrate fits.

28.The type of energy, reduced by the enzymes, for biological reactions to occur is called the: (UHS MDCAT 2019)

  1. Light Energy
  2. Heat energy
  3. Active energy
  4. Activation energy
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Correct answer: (d) Activation energy

An enzyme lowers the activation energy of the reaction.

29.Lock and Key model ws explained by: (UHS MDCAT 2017)

  1. Koshland
  2. Emil Fischer
  3. De Duve
  4. De Duve
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Correct answer: (b) Emil Fischer

Emil Fischer put forward the lock and key model.

30.According to _________ model the active site of enzyme is modified as the substrate interacts with enzyme. (UHS MDCAT 2016)

  1. Induced fit
  2. Lock and Key
  3. Emil Fischer
  4. Fluid Mosaic
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Correct answer: (a) Induced fit

In the induced fit model the active site is moulded round the substrate.

31.Which molecular structure of enzyme is essential for activity of enzyme? (UHS MDCAT 2015)

  1. Primary Structure
  2. Quaternary Structure
  3. Secondary Structure
  4. Tertiary Structure
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Correct answer: (d) Tertiary Structure

The folded tertiary shape is what makes the active site, so activity depends on it.

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