Đề thi, bài tập trắc nghiệm online Hóa sinh enzyme – Đề 12

1. Vmax (maximum velocity) is a key parameter in enzyme kinetics. What is Vmax directly proportional to?

A. The Michaelis-Menten constant (Km).

B. The substrate concentration.

C. The enzyme concentration.

D. The activation energy of the reaction.

2. Allosteric regulation is a mechanism by which enzyme activity is modulated by the binding of a molecule at a site other than the active site. What is this other site called?

A. Catalytic site.

B. Substrate-binding site.

C. Allosteric site.

D. Competitive site.

3. Ligases (or synthetases) are enzymes that catalyze the joining of two molecules. What is typically required for ligase reactions to occur?

A. Water.

B. ATP or another nucleoside triphosphate.

C. An oxidizing agent.

D. A reducing agent.

4. The active site of an enzyme is crucial for its function. What is the PRIMARY role of the active site in enzyme catalysis?

A. To provide structural support to the enzyme molecule.

B. To bind cofactors necessary for enzyme activity.

C. To provide a specific environment for substrate binding and catalysis.

D. To regulate the overall rate of enzyme production in the cell.

5. Hydrolases are enzymes that catalyze hydrolysis reactions. Which type of bond do hydrolases typically break using water?

A. Carbon-carbon bonds.

B. Peptide bonds.

C. Hydrogen bonds.

D. Ionic bonds.

6. Which of the following is an example of enzyme regulation by covalent modification?

A. Feedback inhibition by the end product.

B. Allosteric activation by a substrate.

C. Phosphorylation of an enzyme by a kinase.

D. Competitive inhibition by a structural analog of the substrate.

7. Many enzymes function optimally within a narrow temperature range. What happens to most enzymes if the temperature significantly exceeds their optimal range?

A. Their activity increases indefinitely.

B. They become more stable and efficient.

C. They undergo denaturation and lose activity.

D. Their substrate specificity increases.

8. Temperature significantly affects enzyme activity. What is the general effect of increasing temperature on enzyme activity up to a certain point?

A. It always decreases enzyme activity.

B. It initially increases enzyme activity but then decreases it beyond an optimal temperature.

C. It has no significant effect on enzyme activity.

D. It only increases enzyme activity indefinitely.

9. Feedback inhibition is a common type of enzyme regulation in metabolic pathways. What is the typical regulatory molecule in feedback inhibition?

A. The substrate of the enzyme.

B. The product of the metabolic pathway.

C. ATP.

D. Water.

10. Isoenzymes are multiple forms of an enzyme that catalyze the same reaction but differ in amino acid sequence and properties. What is a common physiological significance of isoenzymes?

A. To increase the overall reaction rate in a cell.

B. To allow for tissue-specific or developmental stage-specific regulation of enzyme activity.

C. To prevent enzyme denaturation at high temperatures.

D. To reduce the specificity of enzymes for their substrates.

11. What is a zymogen or proenzyme?

A. An inactive precursor of an enzyme.

B. A type of enzyme that catalyzes reversible reactions.

C. An enzyme that requires very high substrate concentrations to function.

D. A non-protein enzyme.

12. pH is another crucial factor influencing enzyme activity. Why does pH affect enzyme activity?

A. pH only affects the substrate concentration, not the enzyme itself.

B. pH alters the ionic state of amino acid residues in the enzyme, affecting its structure and active site.

C. pH changes the temperature of the reaction environment.

D. pH directly changes the activation energy of the reaction.

13. Which of the following is NOT a common mechanism for enzyme regulation?

A. Allosteric regulation.

B. Covalent modification.

C. Transcriptional regulation of enzyme synthesis.

D. Increasing the atmospheric pressure.

14. Enzyme specificity refers to the ability of an enzyme to catalyze reactions with specific substrates. Which model BEST describes enzyme-substrate interaction that explains this specificity?

A. The Lock-and-Key model only.

B. The Induced-Fit model only.

C. Both the Lock-and-Key and Induced-Fit models.

D. Neither the Lock-and-Key nor Induced-Fit models are relevant to enzyme specificity.

15. In enzyme-catalyzed reactions, what is the 'transition state'?

A. The final product of the reaction.

B. The enzyme-substrate complex.

C. A high-energy, unstable intermediate in the reaction pathway.

D. The initial substrate before the reaction begins.

16. What is the 'enzyme commission (EC) number' used for in biochemistry?

A. To measure the reaction rate of an enzyme.

B. To classify and name enzymes based on the type of reaction they catalyze.

C. To determine the optimal pH for enzyme activity.

D. To calculate the molecular weight of an enzyme.

17. Some enzymes require metal ions for their activity. What is the role of a metal ion in enzyme catalysis?

A. Metal ions are always competitive inhibitors.

B. Metal ions can act as cofactors, participating in substrate binding, redox reactions, or stabilizing enzyme structure.

C. Metal ions only play a structural role and do not directly participate in catalysis.

D. Metal ions always decrease enzyme activity.

18. Coenzymes are a type of cofactor. What is the MAIN difference between a coenzyme and a prosthetic group?

A. Coenzymes are proteins, while prosthetic groups are not.

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

C. Coenzymes are loosely bound and dissociable from the enzyme, often carrying chemical groups from one reaction to another, while prosthetic groups are tightly bound and permanently associated with the enzyme.

D. Prosthetic groups are organic molecules, while coenzymes are inorganic ions.

19. Transferases are enzymes that catalyze the transfer of functional groups between molecules. What is a common example of a functional group transferred by transferases?

A. Water molecules.

B. Phosphate groups.

C. Carbon dioxide molecules.

D. Nitrogen gas.

20. How does increasing substrate concentration affect the rate of an enzyme-catalyzed reaction, assuming enzyme concentration is constant?

A. It always decreases the reaction rate.

B. It initially increases the reaction rate, but the rate eventually plateaus at Vmax.

C. It has no effect on the reaction rate.

D. It increases the reaction rate indefinitely.

21. Lyases are enzymes that catalyze the breaking of chemical bonds without hydrolysis or oxidation. What is a common feature of reactions catalyzed by lyases?

A. They always require ATP.

B. They often form or remove double bonds.

C. They only operate in anabolic pathways.

D. They always involve water as a reactant.

22. Enzymes are classified into different classes based on the type of reaction they catalyze. To which class does an enzyme belong if it catalyzes oxidation-reduction reactions?

A. Hydrolases.

B. Isomerases.

C. Oxidoreductases.

D. Transferases.

23. Enzyme inhibitors are molecules that reduce the activity of enzymes. How does a competitive inhibitor typically affect enzyme kinetics?

A. It decreases Vmax and increases Km.

B. It increases Vmax and decreases Km.

C. It increases Km but does not affect Vmax.

D. It decreases Vmax but does not affect Km.

24. Enzymes are often used in industrial applications. Which property of enzymes makes them particularly valuable in industrial processes?

A. Their ability to function at extremely high temperatures.

B. Their high specificity and catalytic efficiency.

C. Their ability to be easily synthesized chemically.

D. Their lack of sensitivity to pH changes.

25. Enzymes are crucial in metabolic pathways. What is the role of enzymes in regulating metabolic flux through a pathway?

A. Enzymes do not regulate metabolic flux; it is solely determined by substrate availability.

B. Enzymes accelerate specific reactions, and their activity can be regulated to control pathway flux.

C. Enzymes only determine the direction of metabolic pathways, not the flux.

D. Enzymes are only involved in catabolic pathways, not anabolic ones.

26. Enzyme kinetics studies the rate of enzyme-catalyzed reactions and factors that affect it. What does the Michaelis-Menten constant (Km) represent?

A. The maximum rate of reaction at saturating substrate concentrations.

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

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

D. The equilibrium constant for substrate binding to the enzyme.

27. Isomerases catalyze the interconversion of isomers. What is the primary outcome of a reaction catalyzed by an isomerase?

A. Rearrangement of atoms within a molecule.

B. Joining of two molecules.

C. Breakdown of a large molecule into smaller ones.

D. Transfer of a functional group between molecules.

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

A. Enzymes increase the temperature of the reaction environment.

B. Enzymes lower the activation energy of the reaction.

C. Enzymes increase the concentration of reactants.

D. Enzymes are consumed in the reaction and need to be replenished.

29. Cofactors are non-protein chemical compounds that are essential for the activity of many enzymes. Which of the following is NOT a typical role of a cofactor in enzyme catalysis?

A. To provide additional functional groups for catalysis.

B. To stabilize the enzyme's tertiary structure.

C. To participate directly in the catalytic reaction.

D. To determine the substrate specificity of the enzyme.

30. Non-competitive inhibitors also reduce enzyme activity, but through a different mechanism than competitive inhibitors. How do non-competitive inhibitors affect enzyme kinetics?

A. They increase Km but do not affect Vmax.

B. They decrease Km but do not affect Vmax.

C. They decrease Vmax but do not affect Km.

D. They increase both Vmax and Km.