Đề thi, bài tập trắc nghiệm online Hóa sinh enzyme – Đề 4

1. The Michaelis-Menten constant (Km) is defined as:

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

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

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

D. The turnover number of an enzyme.

2. Enzyme activity is generally most sensitive to changes in pH because pH affects:

A. The temperature of the enzyme.

B. The concentration of the substrate.

C. The ionization state of amino acid residues in the active site.

D. The overall size of the enzyme molecule.

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

A. They increase the activation energy of the reaction.

B. They stabilize the enzyme-substrate complex.

C. They bind to the enzyme more tightly than the substrate, mimicking the transition state.

D. They act as coenzymes in the reaction.

4. Lyases are enzymes that catalyze:

A. Hydrolysis reactions.

B. Oxidation-reduction reactions.

C. Group transfer reactions.

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

5. Isozymes are:

A. Enzymes that catalyze different reactions but use the same substrate.

B. Physically different forms of the same enzyme that catalyze the same reaction.

C. Enzymes that are active only at very high temperatures.

D. Enzymes that require different cofactors for activity.

6. Which statement is TRUE regarding enzyme specificity?

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

B. Enzyme specificity arises from the unique 3D structure of the active site.

C. Enzyme specificity is only determined by the primary structure of the enzyme.

D. All enzymes exhibit absolute specificity for only one substrate.

7. Non-competitive inhibitors affect enzyme activity by:

A. Increasing the Km but not Vmax.

B. Decreasing both Km and Vmax.

C. Decreasing Vmax but not Km.

D. Increasing both Km and Vmax.

8. Irreversible enzyme inhibitors typically function by:

A. Binding to the enzyme active site temporarily.

B. Forming a covalent bond with the enzyme, permanently inactivating it.

C. Changing the enzyme's Km but not Vmax.

D. Binding to an allosteric site and changing enzyme conformation reversibly.

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

A. Allosteric site.

B. Active site.

C. Binding domain.

D. Prosthetic group.

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

A. Non-competitive inhibition.

B. Uncompetitive inhibition.

C. Competitive inhibition.

D. Irreversible inhibition.

11. The 'lock and key' model of enzyme action describes:

A. The conformational change of the enzyme upon substrate binding.

B. The rigid active site of the enzyme that perfectly fits the substrate.

C. The induced fit between enzyme and substrate.

D. The mechanism of competitive inhibition.

12. Feedback inhibition in metabolic pathways typically involves:

A. Activation of the first enzyme in the pathway by the end product.

B. Inhibition of the first enzyme in the pathway by the end product.

C. Activation of the last enzyme in the pathway by the initial substrate.

D. Inhibition of the last enzyme in the pathway by the initial substrate.

13. The 'induced fit' model of enzyme action suggests that:

A. The enzyme active site is always perfectly complementary to the substrate.

B. Both the enzyme and the substrate undergo conformational changes upon binding.

C. Only the substrate changes shape upon binding to the enzyme.

D. This model is only applicable to allosteric enzymes.

14. The optimal temperature for most human enzymes is around:

A. 0°C.

B. 25°C.

C. 37°C.

D. 100°C.

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

A. Temperature.

B. pH.

C. Enzyme concentration.

D. Product concentration (in typical in vivo conditions).

16. Enzymes are highly specific, meaning they:

A. Can catalyze a wide range of reactions.

B. Typically catalyze only one specific reaction or a small set of closely related reactions.

C. Work equally well with all types of substrates.

D. Are active in all cellular compartments.

17. Hydrolases are enzymes that catalyze:

A. Reactions involving water as a reactant to break bonds.

B. Reactions that remove groups to form double bonds.

C. Reactions that change the stereochemistry of molecules.

D. Reactions that combine two molecules using ATP.

18. The Lineweaver-Burk plot is used to:

A. Determine the optimal pH for enzyme activity.

B. Linearize Michaelis-Menten kinetics data for easier determination of Km and Vmax.

C. Separate different isozymes of an enzyme.

D. Measure the temperature stability of an enzyme.

19. Allosteric enzymes are characterized by:

A. Following Michaelis-Menten kinetics strictly.

B. Having a hyperbolic relationship between reaction rate and substrate concentration.

C. Having multiple active sites.

D. Having sigmoidal kinetics due to cooperativity.

20. Isomerases catalyze:

A. The removal of water to form a double bond.

B. The addition of water to break a bond.

C. The rearrangement of atoms within a molecule.

D. The transfer of phosphate groups.

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

A. Zinc ion (Zn2+).

B. Magnesium ion (Mg2+).

C. Nicotinamide adenine dinucleotide (NAD+).

D. Chloride ion (Cl-).

22. Which type of enzyme catalyzes oxidation-reduction reactions?

A. Transferases.

B. Hydrolases.

C. Oxidoreductases.

D. Isomerases.

23. A holoenzyme consists of:

A. Only the protein part (apoenzyme).

B. Only the cofactor.

C. The apoenzyme and the cofactor.

D. Multiple subunits of enzyme molecules.

24. An enzyme cofactor is:

A. The protein part of an enzyme.

B. A non-protein molecule or ion required for enzyme activity.

C. Another name for the substrate.

D. A product of the enzyme-catalyzed reaction.

25. What is the primary function of enzyme kinetics studies?

A. To determine the 3D structure of enzymes.

B. To understand the mechanism of enzyme-catalyzed reactions and factors affecting their rates.

C. To identify the cofactors required by enzymes.

D. To classify enzymes into different groups.

26. Transferases catalyze the:

A. Cleavage of bonds with the addition of water.

B. Transfer of functional groups from one molecule to another.

C. Rearrangement of atoms within a molecule.

D. Joining of two molecules together.

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

A. Hydrolases.

B. Isomerases.

C. Polymerases.

D. Ligases.

28. Ligases catalyze the:

A. Breakdown of large molecules into smaller ones.

B. Formation of bonds, often coupled with ATP hydrolysis.

C. Transfer of electrons between molecules.

D. Rearrangement of functional groups within a molecule.

29. Enzymes are biological catalysts that primarily function by:

A. Increasing the activation energy of a reaction.

B. Decreasing the activation energy of a reaction.

C. Changing the equilibrium constant of a reaction.

D. Being consumed during the reaction process.

30. In competitive inhibition, an inhibitor:

A. Binds only to the enzyme-substrate complex.

B. Binds to the enzyme at a site other than the active site.

C. Increases the Vmax of the enzyme.

D. Binds to the active site of the enzyme, competing with the substrate.