Question 1

1. Which of the following best explains why D symmetry is more common than C symmetry in large oligomeric proteins such as ATCase?

Accepted Answer

D symmetry allows for more subunit interactions, increasing structural stability.

Question 2

2. Glutamine synthetase is described as a dimer of hexamers. Which interface is predicted to be more stable: the interface between two hexamers or the interfaces within a hexamer? Explain your reasoning.

Accepted Answer

The interfaces within a hexamer are more stable due to greater surface area and cooperative interactions.

Question 3

3. Which of the following best describes the symmetry of an oligomeric protein with 12 subunits arranged as two stacked hexameric rings, such as ATCase?

Accepted Answer

$$D_6$$

Question 4

4. Which statement about enzyme catalysis is correct?

Accepted Answer

Enzymes lower the activation energy for the reactions they catalyze.

Question 5

5. Enzymes are potent catalysts because they:

Accepted Answer

Bind the transition state intermediate, stabilizing it and lowering the activation energy.

Question 6

6. Which of the following statements about enzyme-substrate interactions is FALSE?

Accepted Answer

An enzyme generally has higher affinity for its substrate than for a transition state analog.

Question 7

7. Upon substrate binding, the environment of an enzyme active site typically:

Accepted Answer

Decreases its dielectric constant, excluding bulk water.

Question 8

8. When binding a non-chiral substrate, enzymes cannot discriminate between equivalent atoms, such as the two hydrogens on NADH. This is because:

Accepted Answer

The substrate lacks chirality, so the enzyme cannot distinguish between equivalent groups.

Question 9

9. Which of the following is NOT a typical advantage of oligomeric protein structure?

Accepted Answer

Increased susceptibility to denaturation.

Question 10

10. Which of the following best describes the effect of an enzyme on the free energy change ($$\Delta G) of a $$reaction?

Accepted Answer

The enzyme does not change the free energy difference between substrate and product.

Question 11

11. Which of the following statements about the interfaces in oligomeric proteins is correct?

Accepted Answer

Obligatory interfaces are more likely to be hydrophobic than interfaces that are frequently interchanged.

Question 12

12. Which of the following is a plausible evolutionary advantage of protein oligomerization?

Accepted Answer

It allows for allosteric regulation and functional specialization.

Question 13

13. Which of the following best explains why enzymes bind transition states more tightly than substrates or products?

Accepted Answer

Tight binding to the transition state lowers the activation energy ($$\Delta G$$^{\ddagger}$$) and increases the reaction rate.

Question 14

14. A mutation that increases the hydrophilicity of an obligatory interface in a protein oligomer is most likely to:

Accepted Answer

Destabilize the oligomeric structure.

Question 15

15. Which of the following is a correct statement about the effect of enzymes on reaction equilibrium?

Accepted Answer

Enzymes do not change the equilibrium constant ($$K_{eq}) of a $$reaction.

Question 16

16. In a metabolic pathway, an enzyme catalyzes the conversion of substrate S to product P. If the enzyme is inhibited by a transition state analog, what is the most likely effect?

Accepted Answer

The reaction rate will decrease because the analog competes for the active site.

Question 17

17. Which of the following is a key reason why enzymes are highly specific for their substrates?

Accepted Answer

The active site is complementary in shape and chemical properties to the transition state of the substrate.

Question 18

18. Which of the following best describes the role of desolvation in enzyme catalysis?

Accepted Answer

Desolvation reduces the dielectric constant in the active site, enhancing electrostatic interactions.

Question 19

19. Which of the following is a correct statement about the effect of enzyme catalysis on the rate of a reaction?

Accepted Answer

Enzymes increase the rate of reaction by lowering the activation energy ($$\Delta G$$^{\ddagger}$$).

Question 20

20. Which of the following is a likely consequence if an enzyme active site fails to exclude bulk water upon substrate binding?

Accepted Answer

The dielectric constant remains high, weakening electrostatic interactions and reducing catalytic efficiency.

Oligomeric Protein Structure, Symmetry, and Enzyme Catalysis

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