Đề thi, bài tập trắc nghiệm online Hóa sinh enzyme – Đề 14

1. Proteolytic activation (zymogen activation) is a specific type of enzyme regulation. How does proteolytic activation typically work?

A. By binding an activator molecule to the enzyme.

B. By removing a portion of the inactive enzyme precursor (zymogen) through peptide bond cleavage.

C. By increasing the temperature of the enzyme.

D. By changing the pH around the enzyme.

2. Enzymes exhibit specificity, meaning they typically catalyze reactions involving only one or a few substrates. Which model BEST describes the interaction between an enzyme and its substrate that accounts for this specificity?

A. The lock-and-key model.

B. The induced-fit model.

C. The fluid mosaic model.

D. The competitive inhibition model.

3. What is the 'turnover number' (kcat) of an enzyme?

A. The substrate concentration at half Vmax.

B. The maximum reaction rate (Vmax).

C. The number of substrate molecules converted to product per enzyme molecule per unit of time when the enzyme is saturated with substrate.

D. The affinity of the enzyme for its substrate.

4. Ligases, also known as synthases, catalyze the joining of two molecules. What is typically required for a ligase reaction to occur?

A. Water.

B. ATP or another energy source.

C. Oxygen.

D. A reducing agent.

5. Vmax is a crucial parameter in enzyme kinetics. What does Vmax represent?

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

B. The maximum reaction rate when the enzyme is saturated with substrate.

C. The affinity of the enzyme for its substrate.

D. The initial reaction rate at low substrate concentrations.

6. Hydrolases are enzymes that catalyze hydrolysis reactions. What type of reaction does a hydrolase catalyze?

A. Joining two molecules together.

B. Rearranging atoms within a molecule.

C. Breaking a bond using water.

D. Transferring electrons.

7. The active site of an enzyme is crucial for its function. What is the primary role of the active site?

A. To provide structural support to the enzyme.

B. To regulate the enzyme's production in the cell.

C. To bind substrates and catalyze chemical reactions.

D. To transport the enzyme across cell membranes.

8. Cofactors are non-protein chemical compounds that are essential for the biological activity of some enzymes. Which of the following is an example of a cofactor?

A. Glucose.

B. Ribonucleic acid (RNA).

C. Magnesium ions (Mg²⁺).

D. Deoxyribonucleic acid (DNA).

9. Which of the following enzyme regulatory mechanisms involves the covalent attachment of a molecule to the enzyme, often leading to a change in its activity?

A. Allosteric regulation.

B. Feedback inhibition.

C. Covalent modification.

D. Competitive inhibition.

10. Enzymes are crucial in metabolic pathways. What is the role of enzymes in metabolic pathways?

A. To provide energy for cellular processes directly.

B. To slow down biochemical reactions.

C. To catalyze each step of the metabolic pathway, ensuring efficient and regulated flow of metabolites.

D. To store genetic information for the cell.

11. Enzyme activity assays are used to measure the rate of enzyme-catalyzed reactions. Why is it important to control factors like temperature and pH during enzyme assays?

A. To make the enzyme reaction proceed slower.

B. To ensure that the enzyme is fully denatured.

C. To ensure accurate and reproducible measurements of enzyme activity, as enzyme activity is sensitive to temperature and pH.

D. To increase the activation energy of the reaction.

12. Non-competitive inhibitors are another class of enzyme inhibitors. How do non-competitive inhibitors affect Km and Vmax?

A. Increases Km, decreases Vmax.

B. Decreases Km, increases Vmax.

C. Increases Km, no change in Vmax.

D. No change in Km, decreases Vmax.

13. Feedback inhibition is a common regulatory mechanism in metabolic pathways. How does feedback inhibition typically work in enzyme regulation?

A. The substrate of the enzyme inhibits the enzyme's activity.

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

C. An activator molecule enhances the enzyme's activity.

D. Enzymes are activated by their own products.

14. Enzyme inhibitors are molecules that reduce or prevent enzyme activity. Competitive inhibitors affect enzyme kinetics in a specific way. How does a competitive inhibitor affect Km and Vmax?

A. Increases Km, decreases Vmax.

B. Decreases Km, increases Vmax.

C. Increases Km, no change in Vmax.

D. No change in Km, decreases Vmax.

15. Enzymes are classified into six major classes based on the type of reaction they catalyze. Which class of enzymes catalyzes oxidation-reduction reactions?

A. Hydrolases.

B. Isomerases.

C. Oxidoreductases.

D. Transferases.

16. Enzymes are used in various industrial and medical applications. Which of the following is a common application of enzymes in the food industry?

A. Sterilization of medical equipment.

B. Production of antibiotics.

C. Tenderizing meat and clarifying fruit juices.

D. Diagnosis of genetic disorders.

17. Enzyme immobilization is a technique used in industrial enzyme applications. What is enzyme immobilization?

A. The process of destroying enzyme activity.

B. The process of isolating enzymes from cells.

C. The process of confining enzymes to a solid support or within a defined space.

D. The process of purifying enzymes to homogeneity.

18. Allosteric enzymes are regulated by molecules binding at sites other than the active site. What is the term for the site where regulatory molecules bind on an allosteric enzyme?

A. Active site.

B. Catalytic site.

C. Allosteric site.

D. Binding site.

19. Enzyme kinetics studies the rate of enzyme-catalyzed reactions. What does the Michaelis-Menten constant (Km) represent?

A. The maximum rate of reaction at infinite substrate concentration.

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

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

D. The rate constant for the conversion of substrate to product.

20. Uncompetitive inhibition is a less common type of enzyme inhibition. How do uncompetitive inhibitors affect Km and Vmax?

A. Increases Km, decreases Vmax.

B. Decreases Km, decreases Vmax.

C. Increases Km, no change in Vmax.

D. No change in Km, decreases Vmax.

21. Some enzymes require metal ions for their activity. What is the role of these metal ions?

A. To provide structural support to the enzyme only.

B. To participate in redox reactions only.

C. To act as cofactors, participating in substrate binding, active site stabilization, or redox reactions.

D. To regulate gene expression of the enzyme.

22. Enzyme activity can be affected by various factors. How does increasing temperature generally affect the rate of an enzyme-catalyzed reaction up to a certain point?

A. It decreases the reaction rate.

B. It increases the reaction rate.

C. It has no effect on the reaction rate.

D. It initially increases then decreases the reaction rate beyond an optimal temperature.

23. Enzymes are biological catalysts that speed up biochemical reactions. Which of the following statements BEST describes how enzymes achieve this?

A. By increasing the activation energy of the reaction.

B. By decreasing the activation energy of the reaction.

C. By increasing the temperature of the reaction.

D. By decreasing the temperature of the reaction.

24. Isomerases catalyze the interconversion of isomers. What is the main function of isomerase enzymes?

A. To break down molecules into smaller units.

B. To build larger molecules from smaller units.

C. To rearrange atoms within a molecule.

D. To transfer functional groups between molecules.

25. What is the role of coenzymes in enzyme catalysis?

A. To provide structural support to the enzyme.

B. To directly bind to the active site and block substrate binding.

C. To act as carriers of electrons or functional groups in enzymatic reactions.

D. To regulate enzyme production at the genetic level.

26. pH is another critical factor influencing enzyme activity. Most enzymes have an optimal pH range. Why does pH affect enzyme activity?

A. pH changes only affect substrate concentration, not the enzyme itself.

B. pH changes can alter the enzyme's three-dimensional structure and ionization state of amino acid residues in the active site.

C. pH only affects the rate of diffusion of substrates to the enzyme.

D. pH changes the temperature of the reaction mixture.

27. Lyases catalyze the cleavage of bonds by means other than hydrolysis or oxidation. What type of bond cleavage is characteristic of lyase enzymes?

A. Bond cleavage with the addition of water.

B. Bond cleavage through oxidation.

C. Bond cleavage to form double bonds or rings.

D. Bond cleavage by transferring functional groups.

28. In medical diagnostics, enzymes can be used as biomarkers. What does it mean for an enzyme to be used as a biomarker?

A. The enzyme is used to treat a disease directly.

B. The enzyme's presence or concentration in body fluids indicates a particular physiological state or disease.

C. The enzyme is used to synthesize drugs in the body.

D. The enzyme is used to clean medical instruments.

29. Which of the following statements is TRUE regarding enzyme specificity?

A. Enzymes are generally specific for the type of reaction but not for the substrate.

B. Enzymes are generally specific for the substrate but not for the type of reaction.

C. Enzymes exhibit specificity for both the type of reaction catalyzed and the substrate(s) involved.

D. Enzymes are not specific and can catalyze a wide range of reactions with different substrates.

30. Which class of enzymes catalyzes the transfer of functional groups from one molecule to another?

A. Lyases.

B. Ligases.

C. Transferases.

D. Hydrolases.