Đề 7 – Bài tập, đề thi trắc nghiệm online Hóa sinh enzyme

1. Isoenzymes are enzymes that catalyze the same reaction but have different amino acid sequences and may be expressed in different tissues or cellular compartments. What is the PRIMARY physiological significance of isoenzymes?

A. To increase the overall catalytic efficiency of a single reaction type within a cell.

B. To allow for tissue-specific or compartment-specific regulation of metabolic pathways.

C. To prevent enzyme denaturation under extreme conditions.

D. To ensure that enzymes can catalyze multiple different types of reactions.

2. What is the `active site` of an enzyme?

A. The region of the enzyme where regulatory molecules bind.

B. The entire surface of the enzyme protein.

C. A specific region on the enzyme where substrate molecules bind and undergo a chemical reaction.

D. The location in the cell where the enzyme is synthesized.

3. Which statement accurately describes the relationship between enzyme structure and function?

A. Enzyme function is independent of its three-dimensional structure.

B. The primary structure (amino acid sequence) is sufficient to determine enzyme function.

C. The precise three-dimensional structure of an enzyme, especially the active site, is crucial for its specific function.

D. Enzymes are flexible molecules, and their function is not significantly affected by changes in conformation.

4. Allosteric enzymes are regulated by molecules binding at sites other than the active site. Which of the following is a KEY characteristic of allosteric regulation?

A. Allosteric enzymes only follow Michaelis-Menten kinetics.

B. Allosteric regulation always results in enzyme activation.

C. Allosteric enzymes often exhibit sigmoidal kinetics rather than hyperbolic kinetics.

D. Allosteric regulators bind covalently to the enzyme, causing irreversible changes.

5. Competitive and non-competitive inhibition are two major types of enzyme inhibition. How does a competitive inhibitor typically affect the Michaelis-Menten kinetics of an enzyme-catalyzed reaction?

A. It decreases both Vmax and Km.

B. It increases Vmax and decreases Km.

C. It increases Km but does not change Vmax.

D. It decreases Vmax but does not change Km.

6. Feedback inhibition is a common regulatory mechanism in metabolic pathways. In this process, what typically acts as the inhibitor?

A. The substrate of the enzyme being regulated.

B. A molecule structurally similar to the substrate.

C. The final product of the metabolic pathway.

D. An intermediate metabolite in the pathway.

7. Coenzymes and cofactors are essential for the activity of many enzymes. What is the MAIN difference between a coenzyme and a cofactor?

A. Coenzymes are always inorganic, while cofactors are always organic.

B. Coenzymes are loosely bound to the enzyme, while cofactors are tightly bound.

C. Coenzymes are organic molecules, often derived from vitamins, while cofactors can be inorganic ions or organic molecules.

D. Cofactors participate directly in the catalytic reaction, while coenzymes only regulate enzyme activity.

8. Which type of inhibitor binds only to the enzyme-substrate complex, not to the free enzyme?

A. Competitive inhibitor

B. Non-competitive inhibitor

C. Uncompetitive inhibitor

D. Mixed inhibitor

9. Which of the following types of enzyme regulation involves covalent modification, such as phosphorylation or dephosphorylation?

A. Allosteric regulation

B. Feedback inhibition

C. Reversible covalent modification

D. Competitive inhibition

10. Enzyme activity can be affected by several factors. Consider a scenario where the reaction rate of an enzyme-catalyzed reaction increases as substrate concentration increases, but eventually plateaus at a maximum velocity (Vmax). Which factor is primarily responsible for this plateau effect?

A. Temperature denaturation of the enzyme

B. Saturation of enzyme active sites with substrate

C. Competitive inhibition by reaction products

D. Changes in pH leading to enzyme inactivation

11. Michaelis-Menten kinetics describes the relationship between substrate concentration and enzyme reaction rate. What does the Michaelis constant (Km) represent in enzyme kinetics?

A. The maximum velocity of the enzyme-catalyzed reaction.

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

C. The rate constant for the enzyme-substrate complex formation.

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

12. In enzyme kinetics, what does Vmax represent?

A. The substrate concentration required to reach half-maximal velocity.

B. The initial velocity of the reaction at very low substrate concentration.

C. The maximum velocity of the reaction when the enzyme is saturated with substrate.

D. The rate constant for the breakdown of the enzyme-substrate complex.

13. Which of the following is NOT a major class of enzymes according to the Enzyme Commission classification?

A. Isomerases

B. Ligases

C. Polymerases

D. Hydrolases

14. The catalytic efficiency of an enzyme is often described by the kcat/Km ratio. What does a HIGH kcat/Km value indicate about an enzyme?

A. The enzyme has a low affinity for its substrate and a slow turnover rate.

B. The enzyme has a high affinity for its substrate and a fast turnover rate.

C. The enzyme is easily saturated by substrate.

D. The enzyme is strongly inhibited by its products.

15. Enzymes exhibit optimal activity within a specific pH range. If an enzyme`s optimal pH is 7.0, what would be the MOST likely effect on its activity if the pH is drastically lowered to 2.0?

A. The enzyme activity will increase significantly.

B. The enzyme activity will remain unchanged as pH does not affect enzyme structure.

C. The enzyme will undergo denaturation, leading to a significant decrease or loss of activity.

D. The enzyme will become more specific for a wider range of substrates.

16. 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

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

A. Km

B. Vmax

C. 1/Km

D. 1/Vmax

18. Which of the following factors does NOT affect the rate of an enzyme-catalyzed reaction?

A. Enzyme concentration

B. Substrate concentration

C. Presence of inhibitors

D. Volume of the reaction mixture

19. Temperature affects enzyme activity. Generally, enzyme activity increases with temperature up to a certain point, after which it declines sharply. What is the primary reason for the decrease in enzyme activity at high temperatures?

A. Increased kinetic energy of substrate molecules prevents proper binding to the active site.

B. High temperatures cause enzyme denaturation, altering the enzyme`s three-dimensional structure.

C. The reaction becomes exothermic at high temperatures, inhibiting the enzyme.

D. The enzyme active site becomes more rigid, preventing substrate entry.

20. What is the term for the non-protein component that is tightly or covalently bound to an enzyme and is essential for its catalytic activity?

A. Coenzyme

B. Apoenzyme

C. Holoenzyme

D. Prosthetic group

21. What is the term used to describe an enzyme without its necessary cofactor?

A. Holoenzyme

B. Zymogen

C. Apoenzyme

D. Isoenzyme

22. Enzymes are classified into different classes based on the type of reaction they catalyze. To which class does an enzyme that catalyzes the transfer of a phosphate group from ATP to glucose belong?

A. Oxidoreductases

B. Transferases

C. Hydrolases

D. Lyases

23. Some enzymes are secreted as inactive precursors called zymogens or proenzymes. What is the MAIN advantage of synthesizing enzymes in an inactive form?

A. To increase the enzyme`s catalytic efficiency once activated.

B. To allow for rapid synthesis of large quantities of the enzyme.

C. To prevent the enzyme from acting in the wrong location or at the wrong time, potentially causing damage.

D. To simplify the enzyme`s structure and make it more stable.

24. Enzymes are biological catalysts that speed up biochemical reactions. Which of the following statements BEST describes the primary mechanism by which enzymes achieve this?

A. Enzymes increase the temperature of the reaction environment, providing more kinetic energy to reactants.

B. Enzymes are consumed in the reaction, but are regenerated at the end, allowing them to be used repeatedly.

C. Enzymes lower the activation energy required for a reaction to occur, making it easier for reactants to reach the transition state.

D. Enzymes increase the concentration of reactants at the active site, thus driving the reaction forward.

25. The specificity of an enzyme is determined by the unique shape and chemical properties of its active site. What is the term used to describe the model of enzyme-substrate interaction where the active site adjusts its shape to fit the substrate only upon binding?

A. Lock-and-key model

B. Induced-fit model

C. Competitive inhibition model

D. Allosteric regulation model

26. Which of the following statements is TRUE regarding enzyme catalysts?

A. Enzymes are consumed during the reaction and permanently altered.

B. Enzymes alter the equilibrium constant of a reaction, favoring product formation.

C. Enzymes increase the rate of a reaction by providing an alternative reaction pathway with lower activation energy.

D. Enzymes increase the Gibbs free energy change (ΔG) of a reaction, making it more exergonic.

27. What is the role of the transition state in enzyme catalysis?

A. It is a stable intermediate formed during the reaction, easily isolated and studied.

B. It represents the lowest energy point in the reaction pathway.

C. It is a high-energy, unstable intermediate where bonds are being formed and broken.

D. It is the final product complex formed after the reaction is complete.

28. Many enzymes require metal ions for their activity. These metal ions often act as cofactors. Which of the following roles can a metal ion NOT typically play in enzyme catalysis?

A. Stabilizing the enzyme`s tertiary structure.

B. Acting as a reducing agent in redox reactions.

C. Participating directly in substrate binding and orientation.

D. Providing a source of energy for the reaction.

29. How do enzymes affect the equilibrium of a reversible reaction?

A. Enzymes shift the equilibrium towards product formation.

B. Enzymes shift the equilibrium towards reactant formation.

C. Enzymes do not affect the equilibrium; they only accelerate the rate at which equilibrium is reached.

D. Enzymes alter the equilibrium constant (Keq) of the reaction.

30. Consider an enzyme-catalyzed reaction that follows Michaelis-Menten kinetics. If the substrate concentration is equal to Km, what fraction of Vmax will the reaction rate be?

A. 1/4 Vmax

B. 1/2 Vmax

C. 3/4 Vmax

D. Vmax