Đề thi, bài tập trắc nghiệm online Hóa sinh enzyme – Đề 2

1. What is the effect of a catalyst on the equilibrium constant of a reaction?

A. It increases the equilibrium constant.

B. It decreases the equilibrium constant.

C. It does not affect the equilibrium constant.

D. It reverses the equilibrium constant.

2. What is the role of a coenzyme in enzyme catalysis?

A. To permanently bind to the active site and block substrate binding.

B. To provide the enzyme's tertiary structure.

C. To assist in the catalytic reaction, often by carrying electrons or functional groups.

D. To denature the enzyme at high temperatures.

3. In the Lineweaver-Burk plot, what does the y-intercept represent?

A. Km

B. Vmax

C. 1/Km

D. 1/Vmax

4. Enzymes increase reaction rates by:

A. Increasing the temperature of the system.

B. Providing energy to the reaction.

C. Lowering the Gibbs free energy change of the reaction.

D. Lowering the activation energy of the reaction.

5. Hydrolases are characterized by their ability to:

A. Remove water to form new bonds.

B. Add water to break chemical bonds.

C. Rearrange molecules without changing their elemental composition.

D. Transfer electrons between molecules.

6. Which of the following is an example of an enzyme used in the food industry?

A. DNA polymerase

B. Amylase

C. Hemoglobin

D. Insulin

7. In enzyme kinetics, Km (Michaelis constant) is:

A. The maximum reaction rate.

B. The substrate concentration at which the reaction rate is half of Vmax.

C. The enzyme concentration at which the reaction rate is maximum.

D. The dissociation constant of the enzyme-substrate complex.

8. Competitive inhibitors of enzymes work by:

A. Binding to the enzyme at a site other than the active site.

B. Binding irreversibly to the active site.

C. Binding to the active site and preventing substrate binding.

D. Changing the shape of the active site after substrate binding.

9. The optimal pH for most enzymes in the human body is generally:

A. Highly acidic (pH 1-3)

B. Slightly acidic (pH 4-6)

C. Neutral (pH 7)

D. Slightly alkaline (pH 8-10)

10. Oxidoreductases catalyze which type of reactions?

A. Hydrolysis reactions

B. Isomerization reactions

C. Oxidation-reduction reactions

D. Ligation reactions

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

A. Non-competitive inhibition.

B. Uncompetitive inhibition.

C. Competitive inhibition.

D. Mixed inhibition.

12. The 'induced fit' model of enzyme-substrate interaction suggests that:

A. The enzyme's active site is a rigid shape that perfectly matches the substrate.

B. The substrate changes shape to fit into the enzyme's active site.

C. The enzyme's active site changes shape slightly upon substrate binding to achieve optimal fit.

D. Enzyme and substrate shapes are irrelevant for catalysis.

13. Allosteric regulation of enzyme activity involves:

A. Covalent modification of the enzyme's active site.

B. Binding of a molecule at a site other than the active site, affecting enzyme conformation and activity.

C. Direct competition with the substrate for binding to the active site.

D. Irreversible denaturation of the enzyme.

14. Enzymes are biological catalysts that speed up chemical reactions by:

A. Increasing the activation energy of the reaction.

B. Decreasing the activation energy of the reaction.

C. Increasing the temperature of the reaction.

D. Decreasing the temperature of the reaction.

15. The specificity of an enzyme for its substrate is primarily determined by:

A. The overall size of the enzyme molecule.

B. The amino acid sequence of the enzyme.

C. The shape of the enzyme's active site.

D. The presence of cofactors.

16. Non-competitive inhibitors affect enzyme kinetics by primarily changing:

A. Km (Michaelis constant)

B. Vmax (maximum velocity)

C. Both Km and Vmax

D. Neither Km nor Vmax

17. Which of the following best describes the transition state in an enzyme-catalyzed reaction?

A. A stable intermediate in the reaction pathway.

B. The final product of the reaction.

C. A high-energy, unstable intermediate where bonds are being broken and formed.

D. The enzyme-substrate complex before catalysis.

18. Feedback inhibition in metabolic pathways is a type of enzyme regulation where:

A. The substrate of the enzyme inhibits its own production.

B. The end product of a pathway inhibits an enzyme early in the pathway.

C. An activator molecule increases the activity of the first enzyme in the pathway.

D. Enzymes are activated by the accumulation of their products.

19. How do enzymes affect the rate of both the forward and reverse reactions?

A. Enzymes only increase the rate of the forward reaction.

B. Enzymes only increase the rate of the reverse reaction.

C. Enzymes increase the rate of both forward and reverse reactions equally.

D. Enzymes decrease the rate of both forward and reverse reactions equally.

20. Ligases are enzymes responsible for:

A. Breaking down molecules by adding water.

B. Transferring functional groups between molecules.

C. Joining two molecules together, often requiring ATP hydrolysis.

D. Removing groups to form double bonds.

21. Uncompetitive inhibitors bind to:

A. The free enzyme only.

B. The enzyme-substrate complex only.

C. Either the free enzyme or the enzyme-substrate complex.

D. A site unrelated to the enzyme.

22. Which of the following is NOT a major class of enzymes?

A. Hydrolases

B. Lyases

C. Isomerases

D. Polymers

23. Proteolytic activation (zymogen activation) is a regulatory mechanism for enzymes that involves:

A. Phosphorylation of the enzyme to activate it.

B. Binding of an allosteric activator.

C. Cleavage of a peptide bond to convert an inactive precursor into an active enzyme.

D. Removal of a phosphate group to activate the enzyme.

24. Which statement about enzyme classification is correct?

A. Enzymes are classified into four major classes based on their substrate specificity.

B. Enzymes are classified into six major classes based on the type of reaction they catalyze.

C. Enzyme classification is based on their cellular location.

D. Enzyme classification is determined by their molecular weight.

25. What is the primary function of isomerases?

A. To catalyze oxidation-reduction reactions.

B. To catalyze the rearrangement of atoms within a molecule.

C. To catalyze the joining of two molecules.

D. To catalyze the breakdown of large molecules into smaller ones using water.

26. How does temperature generally affect enzyme activity?

A. Enzyme activity decreases linearly with increasing temperature.

B. Enzyme activity increases linearly with increasing temperature.

C. Enzyme activity increases with temperature up to an optimum, then decreases sharply.

D. Temperature has no significant effect on enzyme activity.

27. Transferases are enzymes that facilitate:

A. The cleavage of bonds using water.

B. The transfer of functional groups from one molecule to another.

C. The formation of double bonds.

D. The rearrangement of atoms within a molecule.

28. Which factor does NOT typically affect the rate of an enzyme-catalyzed reaction?

A. Enzyme concentration

B. Substrate concentration

C. Presence of inhibitors or activators

D. The color of the reaction mixture

29. Lyases are enzymes that catalyze:

A. Oxidation-reduction reactions.

B. Transfer of functional groups.

C. Hydrolysis reactions.

D. Cleavage of bonds by means other than hydrolysis or oxidation, often forming double bonds.

30. What is the effect of increasing substrate concentration on enzyme activity in a Michaelis-Menten kinetic model, assuming enzyme concentration is constant?

A. The reaction rate decreases linearly.

B. The reaction rate increases linearly without limit.

C. The reaction rate increases to a maximum value (Vmax) and then plateaus.

D. The reaction rate remains constant regardless of substrate concentration.