Đề 9 – Bài tập, đề thi trắc nghiệm online Hóa sinh enzyme

1. Which class of enzymes catalyzes the transfer of functional groups, such as methyl or phosphate groups, between molecules?

A. Isomerases

B. Ligases

C. Transferases

D. Hydrolases

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

A. Enzyme activity decreases linearly with increasing temperature.

B. Enzyme activity increases linearly with increasing temperature.

C. Enzyme activity initially increases, reaches an optimum, and then decreases.

D. Temperature has no significant effect on enzyme activity.

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

A. Hydrolases

B. Transferases

C. Lyases

D. Oxidoreductases

4. Uncompetitive inhibition occurs when an inhibitor binds only to the enzyme-substrate complex. How does uncompetitive inhibition affect Km and Vmax?

A. Km increases, Vmax decreases

B. Km decreases, Vmax increases

C. Km increases, Vmax remains unchanged

D. Km decreases, Vmax decreases

5. Enzymes are crucial in digestion. Which enzyme is responsible for the initial digestion of carbohydrates in the mouth?

A. Pepsin

B. Trypsin

C. Salivary amylase

D. Lipase

6. Ligases, also known as synthases, catalyze the joining of two molecules. What is typically required for ligase reactions?

A. Water

B. ATP or another energy source

C. Oxygen

D. A cofactor like NAD+

7. Zymogens or proenzymes are inactive enzyme precursors. Why are some enzymes synthesized and stored as zymogens?

A. To prevent enzyme denaturation.

B. To allow for rapid activation of the enzyme when needed.

C. To increase the enzyme`s catalytic efficiency.

D. To simplify enzyme purification.

8. Which statement is TRUE regarding enzyme denaturation?

A. Denaturation always increases enzyme activity.

B. Denaturation involves the breaking of covalent bonds in the enzyme structure.

C. Denaturation leads to a loss of the enzyme`s three-dimensional structure and typically loss of activity.

D. Denaturation only occurs at very low temperatures.

9. Feedback inhibition is a common regulatory mechanism in metabolic pathways. What is the typical effect of the end product of a metabolic pathway on the enzyme catalyzing the first committed step of that pathway in feedback inhibition?

A. Activation

B. Inhibition

C. No effect

D. Increased enzyme synthesis

10. Many enzymes are used in industrial processes. Which enzyme is commonly used in the food industry to tenderize meat?

A. Amylase

B. Lipase

C. Protease (e.g., Papain)

D. Cellulase

11. pH is another crucial factor affecting enzyme activity. Most enzymes have an optimal pH range. Why is pH important for enzyme activity?

A. pH directly affects the concentration of substrate.

B. pH influences the three-dimensional structure of the enzyme and the ionization state of amino acid residues in the active site.

C. pH changes the temperature of the reaction mixture.

D. pH controls the rate of enzyme synthesis in the cell.

12. Enzyme inhibitors are substances that reduce the rate of enzyme-catalyzed reactions. In competitive inhibition, how does the inhibitor affect Km and Vmax?

A. Km increases, Vmax decreases

B. Km decreases, Vmax increases

C. Km increases, Vmax remains unchanged

D. Km remains unchanged, Vmax decreases

13. Non-competitive inhibition is another type of enzyme inhibition. How does a non-competitive inhibitor affect Km and Vmax?

A. Km increases, Vmax decreases

B. Km decreases, Vmax increases

C. Km increases, Vmax remains unchanged

D. Km remains unchanged, Vmax decreases

14. Enzyme activity can be regulated by covalent modification. Phosphorylation is a common type of covalent modification. What is the effect of phosphorylation on enzyme activity in general?

A. Phosphorylation always activates enzymes.

B. Phosphorylation always inhibits enzymes.

C. Phosphorylation can either activate or inhibit enzymes, depending on the enzyme.

D. Phosphorylation has no effect on enzyme activity.

15. Allosteric regulation is a mechanism for controlling enzyme activity. What is the hallmark of allosteric regulation?

A. Inhibition by irreversible inhibitors.

B. Regulation by molecules binding at a site other than the active site.

C. Regulation through changes in temperature.

D. Regulation by competitive inhibitors only.

16. 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 activity

B. Higher enzyme activity and substrate binding affinity

C. Lower substrate binding affinity but higher Vmax

D. Higher Km value

17. 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 at which the reaction rate is maximum.

D. The equilibrium constant for the enzyme-substrate complex formation.

18. Some enzymes require metal ions for their activity. These metal ions often function as:

A. Substrates

B. Products

C. Cofactors

D. Inhibitors

19. Enzyme specificity refers to the ability of an enzyme to catalyze a reaction with only a specific substrate or a small group of structurally related substrates. Which model is commonly used to describe enzyme-substrate interaction and specificity?

A. Lock-and-Key model

B. Induced-Fit model

C. Fluid Mosaic model

D. Koshland model

20. Vmax is a key parameter in enzyme kinetics. What does Vmax signify?

A. The substrate concentration required for maximum enzyme activity.

B. The enzyme concentration at saturation.

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

D. The velocity of the reaction at standard conditions.

21. What is the primary reason enzymes are essential for life?

A. They increase the temperature of biological reactions.

B. They produce energy for cellular processes.

C. They catalyze biochemical reactions at rates necessary to sustain life.

D. They are the building blocks of proteins.

22. What is the effect of increasing substrate concentration on the rate of an enzyme-catalyzed reaction, assuming enzyme concentration is constant and substrate concentration is below saturation levels?

A. The reaction rate decreases.

B. The reaction rate remains constant.

C. The reaction rate increases.

D. The reaction rate fluctuates randomly.

23. Hydrolases are enzymes that catalyze hydrolysis reactions. What type of bond is broken by hydrolases using water?

A. Carbon-carbon bonds

B. Peptide bonds

C. Hydrogen bonds

D. Ionic bonds

24. In the clinical setting, enzymes are used for diagnostic purposes. Elevated levels of which enzyme in the blood are indicative of myocardial infarction (heart attack)?

A. Amylase

B. Alanine transaminase (ALT)

C. Creatine kinase (CK-MB)

D. Alkaline phosphatase

25. 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 bind cofactors necessary for enzyme activity.

C. To bind substrate(s) and catalyze the chemical reaction.

D. To regulate enzyme production within the cell.

26. Lyases catalyze the cleavage of bonds by means other than hydrolysis or oxidation. What type of reaction do lyases typically catalyze?

A. Rearrangement of atoms within a molecule.

B. Joining two molecules together.

C. Formation of double bonds or rings, or cleavage of double bonds or rings.

D. Transfer of electrons between molecules.

27. Which of the following best describes the transition state in an enzyme-catalyzed reaction?

A. The final product of the reaction.

B. The initial substrate molecule.

C. A high-energy, unstable intermediate state during the reaction where bonds are being formed or broken.

D. A stable enzyme-substrate complex.

28. Isomerases catalyze isomerization reactions. What is the primary function of isomerases?

A. To transfer functional groups between molecules.

B. To catalyze oxidation-reduction reactions.

C. To rearrange atoms within a molecule.

D. To break down large molecules into smaller ones using water.

29. Cofactors are non-protein chemical compounds that are required for the biological activity of some enzymes. Which of the following is an example of a cofactor?

A. Glucose

B. Ribonuclease

C. Magnesium ion (Mg²⁺)

D. Deoxyribonucleic acid (DNA)

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

A. Enzymes increase the temperature of the reaction.

B. Enzymes provide energy to the reaction.

C. Enzymes lower the activation energy of the reaction.

D. Enzymes increase the concentration of reactants.