Đề 2 – Bài tập, đề thi trắc nghiệm online Hóa sinh enzyme

1. In enzyme purification, different techniques are used to isolate and purify enzymes. Which technique separates proteins based primarily on their size?

A. Ion exchange chromatography.

B. Affinity chromatography.

C. Size exclusion chromatography.

D. Isoelectric focusing.

2. Enzyme inhibitors are molecules that reduce or prevent enzyme activity. Which type of inhibition is characterized by the inhibitor binding to the active site, directly competing with the substrate?

A. Non-competitive inhibition.

B. Uncompetitive inhibition.

C. Competitive inhibition.

D. Allosteric inhibition.

3. pH also significantly influences enzyme activity. Why does pH affect enzyme activity?

A. pH changes the concentration of substrate.

B. pH alters the three-dimensional structure of the enzyme, including the active site, and can affect ionization of amino acid residues crucial for catalysis and substrate binding.

C. pH affects the temperature of the reaction.

D. pH only affects enzyme activity in extreme acidic conditions.

4. Enzymes are also important in diagnostic medicine. Elevated levels of certain enzymes in blood can indicate tissue damage. Which enzyme is commonly measured to diagnose myocardial infarction (heart attack)?

A. Amylase.

B. Alanine transaminase (ALT).

C. Creatine kinase (CK) and Troponin.

D. Alkaline phosphatase (ALP).

5. Transferases catalyze the transfer of functional groups. Hexokinase is a transferase. What functional group does hexokinase transfer?

A. Amino group.

B. Methyl group.

C. Phosphate group.

D. Carboxyl group.

6. Allosteric enzymes exhibit cooperativity and are regulated by effectors binding at sites other than the active site. Which statement is TRUE regarding allosteric regulation?

A. Allosteric enzymes always follow Michaelis-Menten kinetics.

B. Allosteric inhibitors bind only to the active site.

C. Allosteric effectors can either activate or inhibit enzyme activity.

D. Allosteric regulation only occurs in single-subunit enzymes.

7. Ligases catalyze the joining of two molecules, often coupled with ATP hydrolysis. Which enzyme class does DNA ligase belong to?

A. Hydrolases.

B. Lyases.

C. Ligases.

D. Transferases.

8. Isoenzymes are different forms of an enzyme that catalyze the same reaction but differ in amino acid sequence, regulatory properties, or tissue distribution. What is the physiological significance of isoenzymes?

A. To reduce the overall catalytic capacity of cells.

B. To provide a single enzyme form for all tissues.

C. To allow for fine-tuning of enzyme activity in different tissues or developmental stages, adapting to specific metabolic needs.

D. Isoenzymes have no significant physiological role.

9. Enzyme activity can be regulated by covalent modification. Phosphorylation is a common type of covalent modification. How does phosphorylation typically affect enzyme activity?

A. Phosphorylation always activates enzymes.

B. Phosphorylation always inhibits enzymes.

C. Phosphorylation can either activate or inhibit enzymes, depending on the specific enzyme and the phosphorylation site.

D. Phosphorylation has no effect on enzyme activity.

10. Affinity chromatography is a powerful technique for enzyme purification. What is the basis of separation in affinity chromatography?

A. Charge of the protein.

B. Size of the protein.

C. Specific binding affinity of the protein to a ligand.

D. Hydrophobicity of the protein.

11. Hydrolases catalyze hydrolysis reactions. Which of the following enzymes is a hydrolase?

A. Pyruvate kinase.

B. ATP synthase.

C. Lipase.

D. DNA polymerase.

12. Vmax is a key parameter in enzyme kinetics. What is Vmax?

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

B. The initial rate of the reaction when substrate concentration is very low.

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

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

13. Non-competitive inhibitors reduce enzyme activity by binding to a site other than the active site. What is the effect of a non-competitive inhibitor on Vmax and Km?

A. Increases Vmax, decreases Km.

B. Decreases Vmax, no change in Km.

C. No change in Vmax, increases Km.

D. No change in Vmax, decreases Km.

14. Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex. What is the effect of uncompetitive inhibition on Vmax and Km?

A. Increases Vmax, increases Km.

B. Decreases Vmax, no change in Km.

C. Decreases Vmax, decreases Km.

D. Increases Vmax, decreases Km.

15. Enzymes are used in various industrial and medical applications. Which enzyme is commonly used in laundry detergents to break down protein stains?

A. Amylase.

B. Lipase.

C. Protease.

D. Cellulase.

16. Lactase is an enzyme used to hydrolyze lactose in dairy products for individuals with lactose intolerance. To which class of enzymes does lactase belong?

A. Oxidoreductases.

B. Transferases.

C. Hydrolases.

D. Lyases.

17. 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 synthesis.

C. To bind substrates and facilitate catalysis.

D. To transport the enzyme to its cellular location.

18. Enzyme-linked immunosorbent assay (ELISA) is a widely used biochemical assay that utilizes enzymes for detection. What is the role of the enzyme in ELISA?

A. To capture the antigen.

B. To amplify the detection signal by catalyzing a reaction that produces a detectable product.

C. To label the antibody directly.

D. To purify the target protein.

19. Penicillin is a well-known antibiotic that acts as an enzyme inhibitor. What enzyme does penicillin inhibit in bacteria?

A. DNA gyrase.

B. Ribosomal peptidyl transferase.

C. Transpeptidase (involved in peptidoglycan synthesis).

D. Dihydrofolate reductase.

20. Coenzymes are organic molecules that assist enzymes in catalytic reactions. 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 permanently part of the enzyme`s structure, while prosthetic groups are released after the reaction.

D. Coenzymes are loosely bound to the enzyme and can dissociate, while prosthetic groups are tightly or covalently bound and remain associated with the enzyme.

21. Enzyme classification is based on the type of reaction they catalyze. To which class of enzymes does DNA polymerase belong?

A. Oxidoreductases.

B. Transferases.

C. Hydrolases.

D. Ligases.

22. Isomerases catalyze the rearrangement of atoms within a molecule. Which of the following enzymes is an isomerase?

A. Lactate dehydrogenase.

B. Glucose-6-phosphate isomerase.

C. Ribonuclease.

D. Aminoacyl-tRNA synthetase.

23. Enzymes are crucial in metabolic pathways. Feedback inhibition is a common regulatory mechanism. In feedback inhibition, what typically inhibits the enzyme?

A. The substrate of the enzyme.

B. The product of the metabolic pathway.

C. Another enzyme in the pathway.

D. A cofactor required by the enzyme.

24. Temperature affects enzyme activity. What is the general effect of increasing temperature on enzyme-catalyzed reaction rates up to a certain point?

A. Decreases the reaction rate linearly.

B. Increases the reaction rate linearly indefinitely.

C. Increases the reaction rate up to an optimum temperature, then decreases.

D. Has no effect on the reaction rate.

25. Lyases are enzymes that catalyze the breaking of chemical bonds by means other than hydrolysis or oxidation. Which of the following reactions is MOST likely catalyzed by a lyase?

A. Hydrolysis of a peptide bond.

B. Oxidation of ethanol to acetaldehyde.

C. Removal of a carboxyl group from pyruvate to form acetaldehyde.

D. Formation of a peptide bond between amino acids.

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

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

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

C. The enzyme concentration required for maximum activity.

D. The equilibrium constant of the enzyme-substrate binding.

27. Oxidoreductases catalyze oxidation-reduction reactions. Lactate dehydrogenase is an example. What type of reaction does lactate dehydrogenase catalyze?

A. Hydrolysis of lactate.

B. Isomerization of lactate.

C. Oxidation of lactate to pyruvate.

D. Ligation of lactate molecules.

28. Enzyme specificity refers to the ability of an enzyme to catalyze reactions with specific substrates. Which factor is MOST responsible for enzyme specificity?

A. The enzyme`s molecular weight.

B. The three-dimensional shape of the active site.

C. The enzyme`s concentration in the cell.

D. The temperature of the reaction environment.

29. Enzymes are biological catalysts that accelerate chemical reactions. Which statement BEST describes the mechanism of enzyme action?

A. Enzymes increase the activation energy of reactions, making them proceed faster.

B. Enzymes are consumed during the reaction and need to be replenished.

C. Enzymes provide an alternative reaction pathway with a lower activation energy.

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

30. Proteolytic cleavage is another mechanism of enzyme regulation. Zymogens are inactive enzyme precursors that are activated by proteolytic cleavage. Why are some enzymes synthesized as zymogens?

A. To increase the enzyme`s stability.

B. To allow for rapid activation of the enzyme at the appropriate time and location.

C. To make the enzyme more easily transported across cell membranes.

D. To reduce the enzyme`s catalytic efficiency.