King Edward Medical University Entry Test Biology Enzymes — Set 2

King Edward Medical University Entry Test Biology Enzymes — Set 2

1. Question 1

   Q1. During glycolysis, which enzyme is responsible for converting phosphoenolpyruvate to pyruvate?

   • A) Pyruvate kinase
   • B) Phosphofructokinase
   • C) Aldolase
   • D) Hexokinase

   Answer: Pyruvate kinase

   Explanation: Pyruvate kinase catalyzes this step, unlike phosphofructokinase which acts earlier

2. Question 2

   Q2. What type of inhibition is characterized by the inhibitor binding to the active site of the enzyme?

   • A) Competitive inhibition
   • B) Non-competitive inhibition
   • C) Uncompetitive inhibition
   • D) Allosteric inhibition

   Answer: Competitive inhibition

   Explanation: Competitive inhibition involves direct competition with substrate for the active site

3. Question 3

   Q3. A patient has a deficiency of the enzyme lactate dehydrogenase. Which process would be most affected?

   • A) Glycolysis
   • B) Gluconeogenesis
   • C) Citric acid cycle
   • D) Fatty acid synthesis

   Answer: Glycolysis

   Explanation: Lactate dehydrogenase is crucial for the conversion of pyruvate to lactate during anaerobic glycolysis

4. Question 4

   Q4. What is the term for the non-protein component of an enzyme that is required for its activity?

   • A) Cofactor
   • B) Coenzyme
   • C) Prosthetic group
   • D) Substrate

   Answer: Cofactor

   Explanation: Cofactors can be either inorganic ions or organic compounds like coenzymes

5. Question 5

   Q5. An enzyme has a Km of 0.1 mM and Vmax of 100 μmol/min. What is the significance of the Km value?

   • A) It represents the maximum velocity of the enzyme
   • B) It is the substrate concentration at which the enzyme reaches half of Vmax
   • C) It is the optimal pH for enzyme activity
   • D) It is the energy required for the enzyme to bind to the substrate

   Answer: It is the substrate concentration at which the enzyme reaches half of Vmax

   Explanation: Km is the Michaelis constant, indicating the substrate concentration for half-maximal velocity

6. Question 6

   Q6. Which of the following statements about enzymes is TRUE?

   • A) Enzymes are consumed in the reactions they catalyze
   • B) Enzymes increase the equilibrium constant of a reaction
   • C) Enzymes lower the activation energy of a reaction
   • D) Enzymes change the direction of a reaction

   Answer: Enzymes lower the activation energy of a reaction

   Explanation: Enzymes decrease the activation energy, speeding up the reaction without being consumed

7. Question 7

   Q7. What is the purpose of the enzyme pyruvate carboxylase in gluconeogenesis?

   • A) To convert pyruvate to acetyl-CoA
   • B) To convert pyruvate to oxaloacetate
   • C) To convert oxaloacetate to phosphoenolpyruvate
   • D) To convert fructose-1,6-bisphosphate to fructose-6-phosphate

   Answer: To convert pyruvate to oxaloacetate

   Explanation: Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate, a key step in gluconeogenesis

8. Question 8

   Q8. What is the term for the specific region on an enzyme where the substrate binds?

   • A) Active site
   • B) Binding site
   • C) Catalytic site
   • D) Allosteric site

   Answer: Active site

   Explanation: The active site is where the enzyme-substrate complex forms, facilitating catalysis

9. Question 9

   Q9. An athlete consumes a high-carbohydrate meal before a race. Which enzyme plays a key role in the utilization of this carbohydrate source?

   • A) Hexokinase
   • B) Phosphofructokinase
   • C) Pyruvate kinase
   • D) Lactate dehydrogenase

   Answer: Phosphofructokinase

   Explanation: Phosphofructokinase is a key regulatory enzyme in glycolysis, the primary pathway for carbohydrate utilization

10. Question 10

    Q10. What is the effect of a competitive inhibitor on the Km and Vmax of an enzyme?

    • A) Increases Km, decreases Vmax
    • B) Decreases Km, increases Vmax
    • C) Increases Km, no effect on Vmax
    • D) No effect on Km, decreases Vmax

    Answer: Increases Km, no effect on Vmax

    Explanation: Competitive inhibitors increase the Km by competing with the substrate, without affecting Vmax

11. Question 11

    Q11. Which of the following enzymes is NOT involved in the citric acid cycle?

    • A) Isocitrate dehydrogenase
    • B) Alpha-ketoglutarate dehydrogenase
    • C) Pyruvate kinase
    • D) Aconitase

    Answer: Pyruvate kinase

    Explanation: Pyruvate kinase is a glycolytic enzyme, not part of the citric acid cycle

12. Question 12

    Q12. What is the purpose of the enzyme glucose-6-phosphatase in gluconeogenesis?

    • A) To convert glucose-6-phosphate to glucose
    • B) To convert fructose-6-phosphate to fructose
    • C) To convert pyruvate to oxaloacetate
    • D) To convert phosphoenolpyruvate to pyruvate

    Answer: To convert glucose-6-phosphate to glucose

    Explanation: Glucose-6-phosphatase catalyzes the final step of gluconeogenesis, producing free glucose

13. Question 13

    Q13. A patient has a deficiency of the enzyme fructose-1,6-bisphosphatase. Which process would be most affected?

    • A) Glycolysis
    • B) Gluconeogenesis
    • C) Pentose phosphate pathway
    • D) Fatty acid synthesis

    Answer: Gluconeogenesis

    Explanation: Fructose-1,6-bisphosphatase is a key enzyme in gluconeogenesis, catalyzing the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate

14. Question 14

    Q14. What is the term for the study of the rates of chemical reactions, including enzyme-catalyzed reactions?

    • A) Kinetics
    • B) Thermodynamics
    • C) Equilibrium
    • D) Catalysis

    Answer: Kinetics

    Explanation: Kinetics involves the study of reaction rates and mechanisms, including enzyme kinetics

15. Question 15

    Q15. Which enzyme is involved in the synthesis of fatty acids from acetyl-CoA?

    • A) Acetyl-CoA carboxylase
    • B) Fatty acid synthase
    • C) Fatty acid oxidase
    • D) Lipase

    Answer: Fatty acid synthase

    Explanation: Fatty acid synthase is the enzyme complex responsible for fatty acid synthesis from acetyl-CoA and malonyl-CoA

16. Question 16

    Q16. What is the purpose of the enzyme phosphofructokinase-2 in gluconeogenesis?

    • A) To convert fructose-6-phosphate to fructose-2,6-bisphosphate
    • B) To convert fructose-2,6-bisphosphate to fructose-6-phosphate
    • C) To convert pyruvate to oxaloacetate
    • D) To convert phosphoenolpyruvate to pyruvate

    Answer: To convert fructose-6-phosphate to fructose-2,6-bisphosphate

    Explanation: Phosphofructokinase-2 catalyzes the formation of fructose-2,6-bisphosphate, a potent activator of glycolysis and inhibitor of gluconeogenesis

17. Question 17

    Q17. What is the term for a molecule that provides a transfer site for a functional group in an enzyme-catalyzed reaction?

    • A) Cofactor
    • B) Coenzyme
    • C) Prosthetic group
    • D) Carrier molecule

    Answer: Coenzyme

    Explanation: Coenzymes act as carrier molecules for functional groups, facilitating enzyme catalysis

18. Question 18

    Q18. An enzyme has a high Km value for its substrate. What does this indicate about the enzyme-substrate interaction?

    • A) High affinity
    • B) Low affinity
    • C) High specificity
    • D) Low specificity

    Answer: Low affinity

    Explanation: A high Km indicates low affinity of the enzyme for its substrate, requiring higher substrate concentrations for half-maximal velocity

19. Question 19

    Q19. A nurse administers an anticoagulant to a patient, which works by inhibiting the enzyme prothrombinase. What is the name of this enzyme's cofactor?

    • A) Vitamin K
    • B) Vitamin D
    • C) Calcium
    • D) Vitamin B12

    Answer: Vitamin K

    Explanation: Vitamin K is a cofactor for prothrombinase, essential for blood clotting

20. Question 20

    Q20. In a patient with maple syrup urine disease, which enzyme's deficiency leads to the accumulation of branched-chain amino acids?

    • A) Branched-chain alpha-keto acid dehydrogenase
    • B) Branched-chain aminotransferase
    • C) Isovaleryl-CoA dehydrogenase
    • D) Methylmalonyl-CoA mutase

    Answer: Branched-chain alpha-keto acid dehydrogenase

    Explanation: Branched-chain alpha-keto acid dehydrogenase deficiency causes maple syrup urine disease