Đề 11 – Bài tập, đề thi trắc nghiệm online Hóa sinh enzyme

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

A. The initial substrate of the pathway inhibits the first enzyme.

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

C. An intermediate in the pathway activates the first enzyme.

D. An unrelated molecule activates the final enzyme of the pathway.

2. Zymogens or proenzymes are inactive enzyme precursors. Why are some enzymes synthesized and stored in an inactive form?

A. To increase the enzyme`s stability.

B. To prevent the enzyme from catalyzing reactions in the wrong location or at the wrong time.

C. To make the enzyme easier to transport within the cell.

D. To reduce the enzyme`s production cost for the cell.

3. What is the role of coenzymes in enzyme-catalyzed reactions?

A. To provide structural support to the enzyme.

B. To directly bind the substrate and initiate catalysis.

C. To participate in the catalytic reaction, often by carrying electrons or functional groups.

D. To regulate enzyme production.

4. The catalytic efficiency of an enzyme is often described by the ratio kcat/Km. What does a higher kcat/Km value indicate?

A. Lower enzyme specificity.

B. Higher enzyme affinity for the substrate and faster catalytic rate.

C. Lower enzyme affinity for the substrate and slower catalytic rate.

D. No change in enzyme activity.

5. Lactase is an enzyme important for digestion. What is the substrate of lactase?

A. Sucrose

B. Lactose

C. Maltose

D. Cellulose

6. Isoenzymes are multiple forms of an enzyme that catalyze the same reaction but differ in amino acid sequence and properties. What is a significant physiological advantage of having isoenzymes?

A. Isoenzymes always have higher catalytic activity than single-form enzymes.

B. Isoenzymes allow for tissue-specific or organ-specific regulation of metabolic reactions.

C. Isoenzymes are less sensitive to inhibitors.

D. Isoenzymes simplify metabolic pathways.

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

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

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

C. The enzyme concentration required to reach maximum velocity.

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

8. In the detergent industry, enzymes are added to laundry detergents to improve their cleaning power. Which class of enzymes is MOST commonly used in laundry detergents to remove protein stains?

A. Amylases

B. Lipases

C. Proteases

D. Cellulases

9. Enzyme inhibitors are substances that reduce the activity of enzymes. In competitive inhibition, how does an inhibitor affect enzyme kinetics?

A. It decreases both Km and Vmax.

B. It increases Km but does not change Vmax.

C. It decreases Vmax but does not change Km.

D. It increases both Km and Vmax.

10. Enzyme specificity refers to the enzyme`s ability to discriminate between different substrates. Which model BEST describes the interaction between an enzyme and its substrate that accounts for high specificity?

A. Lock-and-key model

B. Induced-fit model

C. Competitive inhibition model

D. Allosteric regulation model

11. Each enzyme has an optimal pH range for activity. Why does pH affect enzyme activity?

A. pH changes the concentration of substrates.

B. pH alters the enzyme`s primary structure.

C. pH affects the ionization state of amino acid residues in the active site and enzyme conformation.

D. pH changes the temperature of the reaction environment.

12. Temperature and pH are environmental factors that significantly affect enzyme activity. What is the general effect of increasing temperature (within a physiological range) on enzyme activity?

A. Enzyme activity decreases linearly with increasing temperature.

B. Enzyme activity increases linearly with increasing temperature.

C. Enzyme activity generally increases with temperature up to an optimum, then decreases sharply at higher temperatures.

D. Temperature has no significant effect on enzyme activity.

13. Lyases are another class of enzymes. What type of reaction do lyases catalyze?

A. Hydrolysis reactions

B. Isomerization reactions

C. Group transfer reactions

D. Cleavage of bonds by means other than hydrolysis or oxidation, often forming new double bonds or rings.

14. Enzymes are biological catalysts that accelerate biochemical reactions. Which of the following statements BEST describes how enzymes achieve this catalysis?

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

B. Enzymes provide energy to reactants, thus driving the reaction forward.

C. Enzymes lower the activation energy of reactions by providing an alternative reaction pathway.

D. Enzymes increase the temperature of the reaction environment, speeding up the reaction rate.

15. 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 maintain the structural integrity of the enzyme.

B. To bind coenzymes necessary for enzyme activity.

C. To provide a specific environment for substrate binding and chemical reaction.

D. To regulate enzyme production within the cell.

16. Non-competitive inhibition is another type of enzyme inhibition. How does a non-competitive inhibitor affect enzyme kinetics?

A. It increases Km but does not change Vmax.

B. It decreases Km but does not change Vmax.

C. It decreases Vmax but does not change Km.

D. It increases both Km and Vmax.

17. Enzyme immobilization is a technique used in biotechnology and industry. What is the MAIN advantage of enzyme immobilization?

A. It always increases the enzyme`s catalytic activity.

B. It allows for easier recovery and reuse of enzymes, improving process efficiency and reducing costs.

C. It makes enzymes less sensitive to temperature and pH changes.

D. It simplifies enzyme purification processes.

18. Vmax is a crucial parameter in enzyme kinetics. What is Vmax?

A. The substrate concentration at saturation.

B. The initial velocity of the reaction.

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

D. The velocity of the reaction at Km.

19. Enzyme deficiencies can lead to various diseases. Phenylketonuria (PKU) is a genetic disorder caused by a deficiency in which enzyme?

A. Lactase

B. Phenylalanine hydroxylase

C. Glucose-6-phosphate dehydrogenase

D. Pyruvate kinase

20. Enzyme regulation can occur through covalent modification. Which of the following is a common type of covalent modification that regulates enzyme activity?

A. Hydrolysis

B. Phosphorylation

C. Denaturation

D. Competitive inhibition

21. Allosteric regulation is a crucial mechanism for controlling enzyme activity. What is the defining characteristic of allosteric enzymes?

A. They follow Michaelis-Menten kinetics strictly.

B. They have multiple subunits and active sites, and their activity is regulated by molecules binding at sites other than the active site.

C. They are inhibited only by competitive inhibitors.

D. Their activity is solely determined by substrate concentration.

22. In enzyme kinetics, what does the Lineweaver-Burk plot (double reciprocal plot) represent?

A. A plot of reaction velocity versus substrate concentration.

B. A linear plot of 1/V against 1/[S], used to determine Km and Vmax.

C. A plot of enzyme activity versus pH.

D. A plot of enzyme activity versus temperature.

23. Which of the following statements is TRUE regarding enzyme catalysts?

A. Enzymes are consumed during the reaction.

B. Enzymes alter the equilibrium constant of the reaction.

C. Enzymes increase the rate of the forward and reverse reactions equally.

D. Enzymes are highly specific for their substrates and reactions.

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

A. Hydrolases

B. Isomerases

C. Oxidoreductases

D. Transferases

25. Cofactors and coenzymes are essential for the activity of some enzymes. What is the MAIN difference between a cofactor and a coenzyme?

A. Cofactors are organic molecules, while coenzymes are inorganic ions.

B. Cofactors are proteins, while coenzymes are non-protein molecules.

C. Cofactors can be inorganic ions or organic molecules, while coenzymes are organic molecules.

D. Cofactors are loosely bound to the enzyme, while coenzymes are tightly bound.

26. Ligases are enzymes involved in joining molecules together. What is the general type of reaction catalyzed by ligases?

A. Breaking down large molecules into smaller ones.

B. Joining two molecules together, often coupled with ATP hydrolysis.

C. Rearranging atoms within a molecule.

D. Transferring functional groups between molecules.

27. What is the `turnover number` (kcat) of an enzyme?

A. The substrate concentration at half Vmax.

B. The maximum velocity of the reaction.

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

D. The binding affinity of the enzyme for its substrate.

28. What type of bond is NOT typically involved in enzyme-substrate interactions within the active site?

A. Covalent bonds

B. Hydrogen bonds

C. Ionic bonds

D. Van der Waals forces

29. Enzymes are widely used in various industries. In the food industry, which enzyme is commonly used to tenderize meat?

A. Amylase

B. Lipase

C. Protease (e.g., Papain, Bromelain)

D. Cellulase

30. Transition state analogs are powerful tools in enzyme studies and drug design. What are transition state analogs?

A. Substances that resemble the enzyme`s active site.

B. Stable molecules that structurally resemble the transition state of an enzyme-catalyzed reaction.

C. Inhibitors that bind irreversibly to the enzyme.

D. Substrates that are modified to increase enzyme activity.