MDCAT Enzymes MCQs

1. Enzymes are primarily classified as:

A) Proteins
B) Carbohydrates
C) Lipids
D) Nucleic acids

View Answer

2. Which of the following statements best describes enzymes?

A) They increase the activation energy of reactions.
B) They are consumed in chemical reactions.
C) They catalyze biochemical reactions.
D) They work in the absence of substrates.

View Answer

3. Enzymes that catalyze the transfer of functional groups are called:

A) Ligases
B) Oxidoreductases
C) Transferases
D) Hydrolases

View Answer

4. The region on the enzyme where the substrate binds is known as the:

A) Active site
B) Allosteric site
C) Inhibitory site
D) Regulatory site

View Answer

5. The specific substrate for an enzyme is determined by:

A) The enzyme’s active site shape.
B) The temperature of the environment.
C) The pH of the reaction.
D) The concentration of the enzyme.

View Answer

6. Which of the following factors does NOT affect enzyme activity?

A) Temperature
B) pH
C) Presence of inhibitors
D) Color of the enzyme

View Answer

7. Enzymes are specific to:

A) Temperature
B) pH
C) Substrates
D) All of the above

View Answer

8. The process by which an enzyme changes shape to accommodate the substrate is called:

A) Induced fit
B) Lock and key
C) Competitive inhibition
D) Non-competitive inhibition

View Answer

9. Which of the following is a common example of a digestive enzyme?

A) Amylase
B) DNA polymerase
C) Ligase
D) Lysozyme

View Answer

10. The initial rate of an enzyme-catalyzed reaction typically increases with increasing substrate concentration until:

A) The enzyme is denatured.
B) All active sites are saturated.
C) The reaction reaches equilibrium.
D) The temperature increases significantly.

View Answer

11. Which of the following factors can denature an enzyme?

A) High temperature
B) Extreme pH levels
C) Heavy metal ions
D) All of the above

View Answer

12. The enzyme that catalyzes the hydrolysis of sucrose is:

A) Lactase
B) Maltase
C) Sucrase
D) Amylase

View Answer

13. Which of the following is true about enzyme inhibitors?

A) They always increase enzyme activity.
B) They can be reversible or irreversible.
C) They have no effect on enzyme function.
D) They are the same as substrates.

View Answer

14. Competitive inhibitors affect enzyme activity by:

A) Changing the enzyme’s shape.
B) Binding to the active site.
C) Increasing substrate concentration.
D) Lowering activation energy.

View Answer

15. Which of the following best describes the effect of temperature on enzyme activity?

A) Enzyme activity increases with temperature up to a point, then decreases.
B) Enzyme activity decreases continuously with increasing temperature.
C) Enzyme activity is not affected by temperature.
D) Enzyme activity increases indefinitely with temperature.

View Answer

16. The study of enzyme kinetics involves understanding:

A) How enzymes catalyze reactions.
B) The speed of enzyme-catalyzed reactions.
C) The structure of enzymes.
D) All of the above.

View Answer

17. Non-competitive inhibition occurs when the inhibitor:

A) Binds to the active site.
B) Binds to an allosteric site.
C) Increases substrate concentration.
D) Is structurally similar to the substrate.

View Answer

18. Which of the following is a cofactor that assists enzyme activity?

A) ATP
B) NADH
C) Mg²⁺
D) Both B and C

View Answer

19. The maximum rate of reaction for an enzyme is called:

A) Vmax
B) Km
C) Substrate concentration
D) Activation energy

View Answer

20. The Michaelis-Menten constant (Km) represents:

A) The enzyme’s activity at maximum velocity.
B) The substrate concentration at which the reaction rate is half of Vmax.
C) The time taken for the reaction to reach completion.
D) The total number of enzyme molecules in the reaction.

View Answer

21. Which of the following can be a product of enzyme-catalyzed reactions?

A) Proteins
B) Lipids
C) Carbohydrates
D) All of the above

View Answer

22. The effect of pH on enzyme activity is due to:

A) Changes in enzyme shape.
B) Changes in substrate concentration.
C) Temperature variations.
D) The presence of cofactors.

View Answer

23. Enzymes lower the activation energy of a reaction by:

A) Providing an alternative reaction pathway.
B) Increasing the temperature.
C) Decreasing substrate concentration.
D) None of the above.

View Answer

24. The enzyme that breaks down hydrogen peroxide is:

A) Catalase
B) Amylase
C) Lactase
D) Lipase

View Answer

25. Enzyme specificity refers to:

A) The ability of an enzyme to bind multiple substrates.
B) The ability of an enzyme to catalyze a wide range of reactions.
C) The ability of an enzyme to act on a particular substrate.
D) The effect of inhibitors on enzyme activity.

View Answer

26. The term ‘enzyme substrate complex’ refers to:

A) The product formed after enzyme catalysis.
B) The binding of an enzyme and its substrate.
C) The release of the product from the enzyme.
D) The denaturation of the enzyme.

View Answer

27. Enzymes that catalyze the addition of phosphate groups to substrates are known as:

A) Phosphatases
B) Kinases
C) Oxidases
D) Hydrolases

View Answer

28. The effect of substrate concentration on enzyme activity is typically represented by a:

A) Linear graph.
B) Hyperbolic graph.
C) Parabolic graph.
D) Logarithmic graph.

View Answer

29. The activation energy of a reaction is:

A) The energy required to form the enzyme-substrate complex.
B) The energy needed to initiate a reaction.
C) The energy released during a reaction.
D) None of the above.

View Answer

30. Which of the following describes an allosteric enzyme?

A) It has only one active site.
B) It is not affected by inhibitors.
C) It has multiple active sites and can be regulated.
D) It cannot be activated by substrate.

View Answer

31. A reversible inhibitor can:

A) Bind to the enzyme permanently.
B) Displace the substrate permanently.
C) Bind and unbind from the enzyme.
D) Only bind to the active site.

View Answer

32. Which type of enzyme inhibition can be overcome by increasing substrate concentration?

A) Non-competitive inhibition
B) Competitive inhibition
C) Uncompetitive inhibition
D) Irreversible inhibition

View Answer

33. The term ‘denaturation’ refers to:

A) The loss of enzyme activity due to environmental changes.
B) The process of enzyme synthesis.
C) The binding of substrate to an enzyme.
D) The conversion of an inactive enzyme to an active form.

View Answer

34. An enzyme’s activity can be decreased by:

A) Increasing substrate concentration.
B) Increasing temperature within the optimal range.
C) Introducing a competitive inhibitor.
D) Decreasing pH within the optimal range.

View Answer

35. The reaction catalyzed by an enzyme typically results in:

A) The formation of a single product.
B) The formation of multiple products.
C) No change to the enzyme itself.
D) Both A and C.

View Answer

36. Enzymes that facilitate the breakdown of complex molecules are called:

A) Anabolic enzymes
B) Catabolic enzymes
C) Synthases
D) Isomerases

View Answer

37. A coenzyme is:

A) An inorganic molecule that assists enzymes.
B) A type of inhibitor.
C) An organic molecule that assists enzymes.
D) A substrate that binds to enzymes.

View Answer

38. Which of the following is a product of the enzyme lactase?

A) Glucose
B) Galactose
C) Both A and B
D) Lactose

View Answer

39. In competitive inhibition, the inhibitor:

A) Binds to the enzyme at a site other than the active site.
B) Mimics the substrate’s structure.
C) Decreases the enzyme’s activity permanently.
D) Increases the activation energy of the reaction.

View Answer

40. The active site of an enzyme is specifically designed to:

A) Bind to any molecule.
B) Bind only to substrates that fit its shape.
C) Bind to other enzymes.
D) Bind to inhibitors.

View Answer

41. Which of the following affects the enzyme activity by altering the shape of the enzyme?

A) Temperature
B) pH
C) Inhibitors
D) All of the above

View Answer

42. The enzyme that catalyzes the synthesis of RNA from DNA is:

A) DNA polymerase
B) RNA polymerase
C) Ligase
D) Amylase

View Answer

43. The effect of pH on enzyme activity can be explained by:

A) Changes in enzyme conformation.
B) Changes in substrate concentration.
C) The presence of competitive inhibitors.
D) Temperature fluctuations.

View Answer

44. Which enzyme is responsible for the conversion of starch into maltose?

A) Cellulase
B) Amylase
C) Lactase
D) Lipase

View Answer

45. The term “enzyme kinetics” refers to:

A) The study of how enzymes are produced.
B) The study of enzyme activity and reaction rates.
C) The study of enzyme structure.
D) The study of enzyme inhibition.

View Answer

46. Which of the following best describes irreversible inhibition?

A) It can be overcome by increasing substrate concentration.
B) It involves permanent binding of the inhibitor to the enzyme.
C) It does not affect enzyme activity.
D) It can be reversed easily.

View Answer

47. Which of the following is NOT a characteristic of enzymes?

A) They speed up chemical reactions.
B) They are specific for their substrates.
C) They are consumed in the reaction.
D) They lower the activation energy of reactions.

View Answer

48. The optimal pH for most human enzymes is typically around:

A) 2
B) 7
C) 9
D) 12

View Answer

49. Which of the following is a product of the enzyme pepsin?

A) Starch
B) Proteins
C) Lipids
D) Nucleic acids

View Answer

50. The binding of an allosteric inhibitor to an enzyme results in:

A) Activation of the enzyme.
B) No change in enzyme activity.
C) Inhibition of the enzyme’s activity.
D) Formation of the enzyme-substrate complex.

View Answer

51. Enzymes that add functional groups to substrates are known as:

A) Isomerases
B) Transferases
C) Ligases
D) Hydrolases

View Answer

52. Which of the following is true about enzymes?

A) They are always proteins.
B) They can be reused after a reaction.
C) They increase the amount of product formed.
D) They change the equilibrium constant of a reaction.

View Answer

53. The term ‘metabolism’ refers to:

A) The breakdown of molecules only.
B) All the chemical reactions occurring in a cell.
C) The synthesis of proteins only.
D) The movement of molecules across membranes.

View Answer

54. Enzyme specificity is primarily determined by:

A) The temperature.
B) The active site structure.
C) The concentration of substrates.
D) The presence of inhibitors.

View Answer

55. Which of the following factors would likely decrease the rate of an enzyme-catalyzed reaction?

A) Increasing substrate concentration.
B) Increasing temperature to the optimal level.
C) Increasing pH beyond the optimal range.
D) Increasing enzyme concentration.

View Answer

56. Enzymes in the digestive tract function optimally at:

A) Low pH
B) Neutral pH
C) High pH
D) Varying pH depending on the enzyme

View Answer

57. The enzyme involved in the breakdown of proteins into peptides is:

A) Amylase
B) Lipase
C) Protease
D) Sucrase

View Answer

58. A temperature increase typically leads to enzyme activity increasing until:

A) The enzyme becomes saturated with substrate.
B) The enzyme denatures.
C) The substrate is depleted.
D) The pH is altered.

View Answer

59. The enzyme involved in the synthesis of DNA is:

A) RNA polymerase
B) DNA polymerase
C) Ligase
D) Amylase

View Answer

60. The ‘lock and key’ model of enzyme action describes:

A) The binding of substrate to active site.
B) The activation energy of a reaction.
C) The denaturation of enzymes.
D) The regulation of enzyme activity.

View Answer

61. The effect of inhibitors on enzymes can be studied using:

A) Enzyme kinetics
B) pH measurements
C) Temperature measurements
D) Substrate concentration

View Answer

62. Enzymes can become denatured due to:

A) High temperatures
B) Extreme pH levels
C) High salt concentrations
D) All of the above

View Answer

63. Which of the following is an example of an enzyme?

A) Glucose
B) Hemoglobin
C) Lactase
D) DNA

View Answer

64. Inhibitors that resemble the substrate are called:

A) Non-competitive inhibitors
B) Competitive inhibitors
C) Irreversible inhibitors
D) Allosteric inhibitors

View Answer

65. The breakdown of hydrogen peroxide into water and oxygen is catalyzed by:

A) Amylase
B) Catalase
C) Lipase
D) Sucrase

View Answer

66. The concentration of an enzyme is directly proportional to:

A) The rate of reaction.
B) The substrate concentration.
C) The product concentration.
D) The temperature.

View Answer

67. Which of the following statements is true about coenzymes?

A) They are permanently bound to the enzyme.
B) They are typically inorganic.
C) They assist enzymes in their function.
D) They are not required for enzyme activity.

View Answer

68. The enzyme that catalyzes the hydrolysis of fats is:

A) Amylase
B) Protease
C) Lipase
D) Sucrase

View Answer

69. Enzymes can be denatured by all of the following EXCEPT:

A) Extreme pH
B) High temperature
C) Increasing substrate concentration
D) High salt concentration

View Answer

70. Which of the following would result in an increase in reaction rate?

A) Adding a non-competitive inhibitor
B) Decreasing temperature
C) Increasing substrate concentration up to a point
D) Decreasing enzyme concentration

View Answer

71. The term “apoenzyme” refers to:

A) The active form of an enzyme.
B) The inactive form of an enzyme.
C) The enzyme-substrate complex.
D) The enzyme with its cofactor.

View Answer

72. The effect of temperature on enzyme activity can be described as:

A) Linear
B) Hyperbolic
C) Bell-shaped
D) Exponential

View Answer

73. What is the primary function of enzymes in biochemical reactions?

A) To change the products of the reaction.
B) To lower the activation energy.
C) To act as reactants.
D) To provide energy for the reaction.

View Answer

74. The enzyme involved in the breakdown of lactose is:

A) Maltase
B) Lactase
C) Amylase
D) Sucrase

View Answer

75. The action of the enzyme catalase can be measured by:

A) The rate of substrate consumption.
B) The rate of product formation.
C) The amount of oxygen released.
D) All of the above.

View Answer

76. What is the role of allosteric sites in enzymes?

A) They are the main active sites for substrate binding.
B) They regulate enzyme activity through the binding of molecules.
C) They permanently deactivate the enzyme.
D) They provide structural support.

View Answer

77. Which of the following describes the saturation of an enzyme?

A) The active site is occupied by an inhibitor.
B) All active sites are occupied by substrate.
C) The enzyme is denatured.
D) The enzyme is inactive.

View Answer

78. Enzymes can be classified based on their:

A) Source
B) Function
C) Structure
D) All of the above

View Answer

79. The ability of an enzyme to catalyze a reaction is affected by:

A) Environmental conditions
B) Substrate concentration
C) Enzyme concentration
D) All of the above

View Answer

80. The enzyme that catalyzes the hydrolysis of starch is:

A) Lipase
B) Amylase
C) Protease
D) Lactase

View Answer

81. Enzymes are typically named after:

A) Their structure
B) Their function or substrate
C) Their source
D) Their mechanism

View Answer

82. A cofactor that is a metal ion is classified as:

A) Coenzyme
B) Prosthetic group
C) Inhibitor
D) None of the above

View Answer

83. Which of the following is NOT a characteristic of enzymes?

A) They lower activation energy.
B) They are specific to substrates.
C) They are permanently changed after the reaction.
D) They can be reused multiple times.

View Answer

84. The substrate is:

A) The product of the enzyme reaction.
B) The molecule upon which an enzyme acts.
C) The enzyme itself.
D) An inhibitor of the enzyme.

View Answer

85. The lock and key model of enzyme activity suggests:

A) The enzyme can fit many substrates.
B) The enzyme’s active site is rigid and specific.
C) The substrate can modify the enzyme shape.
D) The enzyme can function without a substrate.

View Answer

86. The main role of proteases is to:

A) Break down carbohydrates.
B) Hydrolyze proteins into amino acids.
C) Synthesize proteins.
D) Hydrolyze lipids.

View Answer

87. Which type of inhibition does not compete with the substrate for the active site?

A) Competitive inhibition
B) Non-competitive inhibition
C) Uncompetitive inhibition
D) Both B and C

View Answer

88. Enzymes are affected by inhibitors because:

A) They change the enzyme’s substrate.
B) They alter the shape or activity of the enzyme.
C) They increase the enzyme’s temperature.
D) They reduce substrate concentration.

View Answer

89. Which of the following describes enzyme specificity?

A) An enzyme can bind to multiple substrates.
B) An enzyme can only catalyze one specific reaction.
C) An enzyme can function in a wide range of reactions.
D) None of the above.

View Answer

90. What is the effect of increasing enzyme concentration on reaction rate?

A) It decreases reaction rate.
B) It has no effect on reaction rate.
C) It increases reaction rate until saturation is reached.
D) It decreases the activation energy required.

View Answer

91. The term ‘enzymatic activity’ refers to:

A) The structural integrity of the enzyme.
B) The ability of an enzyme to catalyze a reaction.
C) The amount of substrate present.
D) The temperature of the reaction.

View Answer

92. Which enzyme is responsible for synthesizing DNA?

A) DNA polymerase
B) RNA polymerase
C) Ligase
D) Amylase

View Answer

93. The relationship between substrate concentration and enzyme activity can be described by:

A) Linear equations.
B) The Michaelis-Menten equation.
C) The first law of thermodynamics.
D) The second law of thermodynamics.

View Answer

94. Enzyme inhibitors can be used in medicine to:

A) Enhance enzyme activity.
B) Slow down metabolic reactions.
C) Control disease progression.
D) Both B and C.

View Answer

95. Which of the following is an allosteric inhibitor?

A) One that binds to the active site.
B) One that binds to a site other than the active site.
C) One that increases enzyme activity.
D) One that is structurally similar to the substrate.

View Answer

96. The rate of an enzyme-catalyzed reaction can be affected by:

A) The presence of products.
B) Substrate concentration.
C) Temperature.
D) All of the above.

View Answer

97. What is the primary role of cofactors in enzyme activity?

A) To increase the activation energy.
B) To enhance the binding of substrates.
C) To serve as substrates themselves.
D) To inhibit the enzyme action.

View Answer

98. The reaction velocity of an enzyme-catalyzed reaction is defined as:

A) The rate of substrate consumption.
B) The amount of product formed per unit time.
C) The activation energy required.
D) The concentration of enzyme used.

View Answer

99. Which of the following is NOT a factor that affects enzyme activity?

A) Temperature
B) pH
C) Presence of competitive substrates
D) The color of the enzyme

View Answer

100. The main function of enzymes in metabolic pathways is to:

A) Provide energy for the reactions.
B) Increase the rate of reactions.
C) Change the products of the reactions.
D) Decrease the number of reactions.

View Answer