Đề thi, bài tập trắc nghiệm online Hóa sinh enzyme – Đề 10

1. Feedback inhibition is a type of enzyme regulation where:

A. The substrate inhibits the enzyme.

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

C. An activator molecule enhances enzyme activity.

D. Enzyme concentration is increased to enhance product formation.

2. Allosteric regulation of enzymes typically involves:

A. Covalent modification of the enzyme.

B. Binding of regulatory molecules at a site other than the active site.

C. Direct competition for the active site.

D. Irreversible denaturation of the enzyme.

3. In enzyme kinetics, the Lineweaver-Burk plot is used to:

A. Determine the primary structure of an enzyme.

B. Linearize the Michaelis-Menten equation for easier determination of Km and Vmax.

C. Measure the enzyme's molecular weight.

D. Identify the active site of an enzyme.

4. The 'induced fit' model of enzyme action differs from the 'lock and key' model in that:

A. It involves irreversible enzyme inhibition.

B. It suggests the active site is flexible and changes shape upon substrate binding.

C. It only applies to enzymes with multiple substrates.

D. It describes enzyme denaturation.

5. Trypsinogen is an example of a:

A. Coenzyme.

B. Holoenzyme.

C. Zymogen.

D. Competitive inhibitor.

6. The optimum pH for most human enzymes is typically around:

A. pH 2 (highly acidic).

B. pH 7 (neutral).

C. pH 10 (highly alkaline).

D. pH 14 (extremely alkaline).

7. What is the 'lock and key' model of enzyme action?

A. The enzyme changes shape to accommodate the substrate.

B. The active site is rigid and perfectly complementary to the substrate shape.

C. The enzyme and substrate bind randomly.

D. The substrate modifies the enzyme structure after binding.

8. Temperature and pH affect enzyme activity by primarily altering the enzyme's:

A. Substrate specificity.

B. Primary structure.

C. Three-dimensional conformation.

D. Molecular weight.

9. What effect does a non-competitive inhibitor have on 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.

10. Isoenzymes are:

A. Enzymes that catalyze different reactions but have similar structures.

B. Different enzymes that catalyze the same reaction but have different properties.

C. Enzymes that are active in their zymogen form.

D. Enzymes that are irreversibly inhibited.

11. Phosphorylation is a common type of:

A. Competitive inhibition.

B. Non-competitive inhibition.

C. Covalent modification for enzyme regulation.

D. Enzyme denaturation.

12. The region of an enzyme where substrate molecules bind and undergo a chemical reaction is called the:

A. Allosteric site.

B. Active site.

C. Competitive site.

D. Non-competitive site.

13. Zymogens or proenzymes are:

A. Active enzymes that require cofactors.

B. Inactive precursor forms of enzymes.

C. Enzymes that catalyze reversible reactions.

D. Enzymes that are only active at low temperatures.

14. Enzymes are classified into major classes based on:

A. Their molecular weight.

B. The type of reaction they catalyze.

C. Their cellular location.

D. Their subunit composition.

15. Enzymes primarily function by:

A. Increasing the activation energy of a reaction.

B. Decreasing the activation energy of a reaction.

C. Increasing the temperature of the reaction.

D. Decreasing the temperature of the reaction.

16. What effect does a competitive inhibitor have on 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.

17. Coenzymes are a type of:

A. Competitive inhibitor.

B. Non-competitive inhibitor.

C. Cofactor.

D. Substrate.

18. The Michaelis-Menten constant (Km) is:

A. The maximum rate of an enzyme-catalyzed reaction.

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

C. The equilibrium constant for enzyme-substrate binding.

D. Independent of substrate concentration.

19. Competitive inhibitors affect enzyme activity by:

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

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

C. Decreasing the Vmax of the enzyme.

D. Increasing the Km of the enzyme, but not affecting Vmax.

20. Apoenzyme refers to:

A. The active form of an enzyme with its cofactor.

B. The inactive protein component of an enzyme, lacking its cofactor.

C. An enzyme that catalyzes reversible reactions.

D. An enzyme with multiple active sites.

21. Non-competitive inhibitors differ from competitive inhibitors because they:

A. Bind only to the enzyme-substrate complex.

B. Bind irreversibly to the active site.

C. Bind to a site other than the active site, altering enzyme conformation.

D. Increase the enzyme's affinity for the substrate.

22. Which of the following is an example of a coenzyme?

A. Iron (Fe2+).

B. Zinc (Zn2+).

C. Nicotinamide adenine dinucleotide (NAD+).

D. Chloride (Cl-).

23. Holoenzyme refers to:

A. The inactive protein component of an enzyme.

B. The enzyme without its substrate.

C. The active form of an enzyme, including its cofactor.

D. An enzyme that only functions at high temperatures.

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

A. They are highly specific for their substrates.

B. They are consumed during the reaction.

C. They increase the rate of chemical reactions.

D. They are proteins (mostly).

25. Lyases catalyze:

A. Joining of two molecules coupled with ATP hydrolysis.

B. Transfer of functional groups.

C. Cleavage of bonds by means other than hydrolysis or oxidation.

D. Reactions involving electron transfer.

26. Which factor does NOT typically affect enzyme activity?

A. Substrate concentration.

B. Enzyme concentration.

C. Product concentration.

D. Gravitational force.

27. Hydrolases are enzymes that catalyze:

A. Oxidation-reduction reactions.

B. Transfer of functional groups.

C. Hydrolysis reactions.

D. Isomerization reactions.

28. Vmax represents:

A. The substrate concentration at half-maximal velocity.

B. The Michaelis-Menten constant.

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

D. The initial rate of reaction.

29. Cofactors are:

A. Protein components of enzymes.

B. Organic molecules that bind tightly to enzymes.

C. Non-protein chemical compounds required for enzyme activity.

D. Enzyme inhibitors.

30. What information can be derived from the slope of a Lineweaver-Burk plot?

A. Vmax.

B. Km.

C. Km/Vmax.

D. 1/Vmax.