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Free Enzymes MCQs with Answers

633 Enzymes MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Enzymes are biological catalysts that lower activation energy without being consumed, and their specificity is explained by the lock and key and induced fit models. Work includes the effects of temperature, pH and substrate concentration on reaction rate, plus competitive and non-competitive inhibition and how these differ.

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Characteristics of EnzymesMode of Enzyme ActionFactors Affecting Enzyme ActionEnzyme Inhibitors
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633 questions · page 9 of 32

161. The enzyme substrate complex is formed during :

  • A. Induced fit model
  • B. Lock and key model
  • C. Both A and B
  • D. None

Explanation: Both models involve temporary formation of an enzyme-substrate complex.

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Correct answer: Both A and B

162. An example of competitive inhibition of an enzyme is the inhibition of:

  • A. Succinic dehydrogenase by malonic acid
  • B. Cytochrome oxidase by cyanide
  • C. Hexokinase by glucose
  • D. Carbonic anhydrase by carbon dioxide

Explanation: The inhibition of succinic dehydrogenase by malonic acid is an example of competitive inhibition.

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Correct answer: Succinic dehydrogenase by malonic acid

163. The inhibitor which closely resembles the substrate in its molecular structure and inhibits the enzyme activity by binding to the active site of the enzyme is called:

  • A. Feedback inhibitor
  • B. Non-competitive inhibitor
  • C. Allosteric modulator
  • D. Competitive inhibitor

Explanation: In competitive inhibition, the inhibitor (I) closely resembles the real substrate (S), and is regarded as a substrate analogue.

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Correct answer: Competitive inhibitor

164. The following statements are about enzymes: 1. They are globular proteins except ribo-enzyme.2. They can be inhibited3. They are formed in the smooth endoplasmic reticulum 4. There are only found attached to Plasma membranes in the cell Which statements are correct for all enzymes?

  • A. 1 and 4
  • B. 2 and 4
  • C. 1 and 2
  • D. 1,2,3 and 4

Explanation: Enzymes are a type of protein, and they have a three-dimensional, globular shape.

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Correct answer: 1 and 2

165. The enzyme in breast milk that causes the coagulation of milk or forms precipitates of milk is:

  • A. Rennin
  • B. Trypsin
  • C. Amylase
  • D. Lipase

Explanation: Rennin, also known as chymosin, is an enzyme that plays a key role in the coagulation of milk proteins, particularly casein.

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Correct answer: Rennin

166. Enzymes that are functioning within the cell are called:

  • A. Endoenzymes
  • B. Exoenzymes
  • C. Holoenzymes
  • D. Both A & C

Explanation: Endoenzymes are enzymes that act within the cell, and their catalytic activity is confined to the interior of the cell.

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Correct answer: Endoenzymes

167. Which of the following factors affect enzyme activity?

  • A. Temperature
  • B. pH
  • C. Concentration of substrate
  • D. Radiation
  • E. All of these

Explanation: All of these factors can influence enzyme activity:Temperature: Enzymes generally work faster with rising temperatures until they reach an…

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Correct answer: All of these

168. An enzyme increases the speed of a reaction:

  • A. By adding activation energy requirements.
  • B. By lowering the activation energy requirements.
  • C. By altering the equilibrium of the reaction.
  • D. By changing the concentration of products.

Explanation: Enzymes serve as biological catalysts that increase the rate of chemical reactions by lowering the activation energy required for the…

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Correct answer: By lowering the activation energy requirements.

169. The enzyme found in saliva responsible for the digestion of carbohydrates is:

  • A. Lysozyme
  • B. Amylase
  • C. Pepsin
  • D. Trypsinogen
  • E. Lipase

Explanation: The enzyme found in saliva responsible for the digestion of carbohydrates is amylase.

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Correct answer: Amylase

170. Enzymes work by lowering the _ of the reactions they catalyse:

  • A. Kinetic energy
  • B. Activation energy
  • C. Heat energy
  • D. Potential energy

Explanation: Activation Energy is the minimum amount of energy that the reacting species must possess in order to undergo a specified reaction.

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Correct answer: Activation energy

171. L - Asparaginase enzyme has been used for the treatment of:

  • A. Jaundice
  • B. Blood cancer
  • C. Rickets
  • D. Heart disease

Explanation: L-asparaginase is an enzyme that has been used in the treatment of certain types of cancer, particularly acute lymphoblastic leukemia.

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Correct answer: Blood cancer

172. Which of the following enzymes is raised in rickets?

  • A. Lactic dehydrogenase
  • B. LDH - I
  • C. Phosphatase
  • D. Alkaline phosphatase

Explanation: 'Rickets' is a condition that leads to a developmental defect in children because of the lack of Vitamin D and calcium in their diet.

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Correct answer: Alkaline phosphatase

173. Due to the similarity of structure, competitive inhibitors may be selected by the _ site.

  • A. Catalytic
  • B. Active
  • C. Binding
  • D. Allosteric

Explanation: Competitive inhibitors are structurally similar to the substrate and therefore can bind to the same region of the enzyme where the…

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Correct answer: Active

174. Identify the wrong statements.(a) The substrate binds to active site of enzyme and does not fit into active site(b) The binding of substrate induces the enzyme to alter its shape(c) Chemical bonds of substrate break down not to form new enzyme-product complex(d) The enzyme releases the products of the reaction and runs through catalytic cycle once again

  • A. A, C
  • B. B, D
  • C. B, C
  • D. A, D

Explanation: The question asks to identify the wrong statements regarding enzyme function.1.

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Correct answer: A, C

175. Optimum temperature for enzymes of human body is:

  • A. 90 °F
  • B. 95 °F
  • C. 98 °F
  • D. 100 °F

Explanation: The optimum temperature for an enzyme is the temperature at which the enzyme catalyzes a reaction at the highest rate.

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Correct answer: 98 °F

176. The cofactor usually acts as "bridge" between:

  • A. Enzyme & substrate
  • B. Enzyme & product
  • C. Coenzyme & substrate
  • D. Activator & substrate

Explanation: Cofactors are non-protein molecules that are required for enzymes to work.

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Correct answer: Enzyme & substrate

177. What is true about the induced fit model:

  • A. Explains mechanism of enzyme action
  • B. Enzyme is specific in nature
  • C. Enzyme is a flexible structure
  • D. Enzyme show change during reaction

Explanation: Option A: The induced fit model is a model that explains how enzymes work.

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Correct answer: Enzyme is a flexible structure

178. The optimum pH of catalase is:

  • A. Slightly alkaline
  • B. Highly acidic
  • C. Highly alkaline
  • D. Slightly acidic

Explanation: The optimum pH of catalase is slightly alkaline, with a range of 6.8 to 7.2.

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Correct answer: Slightly alkaline

179. Cyanide for enzymes act as:

  • A. Substrate
  • B. Prosthetic group
  • C. Cofactor
  • D. Inhibitor

Explanation: Option A: A substrate is a molecule that an enzyme works on. Enzymes are proteins that help to speed up chemical reactions in the body.

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Correct answer: Inhibitor

180. Enzymes are _ that catalyze chemical living organisms and are very specific in their action.

  • A. Proteins
  • B. Vitamins
  • C. Lipids
  • D. Minerals

Explanation: Enzymes are biological molecules, and the majority of them are proteins.

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Correct answer: Proteins
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