Protein Techniques exam 2

1. What does thermodynamics primarily tell us about a chemical reaction?

A. How quickly the reaction occurs

B. Whether the reaction is energetically favorable

C. Which enzyme catalyzes the reaction

D. How much enzyme is present

B. Whether the reaction is energetically favorable

What does thermodynamics primarily tell us about a chemical reaction?

Whether the reaction is energetically favorable

2. What does kinetics primarily describe?

A. Whether a reaction is thermodynamically favorable

B. The equilibrium constant only

C. How fast a reaction occurs

D. The structure of DNA

C. How fast a reaction occurs

2. What does kinetics primarily describe?

How fast a reaction occurs

3. A reaction has ΔG < 0. What does this mean?

A. The reaction cannot occur

B. The reaction is thermodynamically favorable

C. The reaction must occur immediately

D. The reaction requires an enzyme

B. The reaction is thermodynamically favorable

3. A reaction has ΔG < 0. What does this mean?

The reaction is thermodynamically favorable

4. Why might a thermodynamically favorable reaction occur very slowly?

A. Its products are always unstable

B. It has a high activation-energy barrier

C. ΔG is always positive

D. Enzymes prevent favorable reactions

B. It has a high activation-energy barrier

4. Why might a thermodynamically favorable reaction occur very slowly?

It has a high activation-energy barrier

5. What is activation energy?

A. Energy released when products form

B. Energy stored permanently in products

C. Energy required to destabilize the existing state and reach the transition state

D. Energy required to destroy an enzyme

C. Energy required to destabilize the existing state and reach the transition state

5. What is activation energy?

Energy required to destabilize the existing state and reach the transition state

6. What happens when an enzyme catalyzes a reaction?

A. ΔG becomes more negative

B. ΔG becomes zero

C. Activation energy decreases

D. The equilibrium changes permanently

C. Activation energy decreases

6. What happens when an enzyme catalyzes a reaction?

Activation energy decreases

7. Which statement about enzymes is correct?

A. Enzymes change the thermodynamic favorability of a reaction

B. Enzymes increase activation energy

C. Enzymes lower activation energy

D. Enzymes are permanently consumed

C. Enzymes lower activation energy

7. Which statement about enzymes is correct?

Enzymes lower activation energy

8. Why do enzymes allow many reactions to occur at reasonable temperatures?

A. They eliminate all molecular collisions

B. They lower the activation-energy barrier

C. They increase ΔG

D. They prevent substrate binding

B. They lower the activation-energy barrier

8. Why do enzymes allow many reactions to occur at reasonable temperatures?

They lower the activation-energy barrier

9. For a chemical reaction to occur, molecules generally need to:

A. Collide randomly at any angle

B. Avoid each other

C. Meet, have appropriate orientation, and have sufficient energy

D. Always be at 0°C

C. Meet, have appropriate orientation, and have sufficient energy

9. For a chemical reaction to occur, molecules generally need to:

Meet, have appropriate orientation, and have sufficient energy

10. Which is an example of a productive collision?

A. Molecules collide with insufficient energy

B. Molecules collide in an orientation that allows bonds to form or break

C. Molecules never interact

D. Molecules collide but are permanently separated

B. Molecules collide in an orientation that allows bonds to form or break

10. Which is an example of a productive collision?

Molecules collide in an orientation that allows bonds to form or break

11. What is one major advantage of an enzyme's active site?

A. It prevents substrates from interacting

B. It brings substrates together in a favorable orientation

C. It increases substrate randomness

D. It destroys substrate before binding

B. It brings substrates together in a favorable orientation

11. What is one major advantage of an enzyme's active site?

It brings substrates together in a favorable orientation

12. The reactants that bind to an enzyme are called:

A. Products

B. Cofactors

C. Substrates

D. Coenzymes

C. Substrates

12. The reactants that bind to an enzyme are called:

substrates

13. What is the active site?

A. The entire enzyme

B. The region where substrate binds and catalysis occurs

C. The product released by an enzyme

D. A separate enzyme

B. The region where substrate binds and catalysis occurs

14. Enzyme specificity is primarily related to:

A. The enzyme's specific 3-D structure and functional groups

B. The enzyme's color

C. The temperature alone

D. The amount of water present

A. The enzyme's specific 3-D structure and functional groups

14. Enzyme specificity is primarily related to:

A. The enzyme's specific 3-D structure and functional groups

15. Why does an enzyme bind some substrates but not others?

A. All substrates bind equally

B. The active site has specific shape and chemical properties

C. Enzymes randomly select substrates

D. Substrates choose enzymes based only on temperature

B. The active site has specific shape and chemical properties

15. Why does an enzyme bind some substrates but not others?

B. The active site has specific shape and chemical properties

16. Which model describes an enzyme changing shape around its substrate?

A. Lock-and-key only

B. Induced fit

C. Random collision

D. Thermodynamic equilibrium

B. Induced fit

16. Which model describes an enzyme changing shape around its substrate?

Induced fit

17. Who is associated with the induced-fit model?

A. Fischer

B. Koshland

C. Watson

D. Mendel

B. Koshland

17. Who is associated with the induced-fit model?

Koshland

18. Who is associated with the lock-and-key model?

A. Fischer

B. Koshland

C. Franklin

D. Darwin

A. Fischer

18. Who is associated with the lock-and-key model?

A. Fischer

19. What happens during induced fit?

A. The enzyme is destroyed

B. Substrate binding causes the enzyme to adjust its shape

C. The substrate permanently changes into an enzyme

D. The active site disappears

B. Substrate binding causes the enzyme to adjust its shape

19. What happens during induced fit?

B. Substrate binding causes the enzyme to adjust its shape

20. Why is substrate orientation important?

A. It increases nonproductive collisions

B. It positions reactive groups so the reaction can occur efficiently

C. It prevents bond formation

D. It changes ΔG

B. It positions reactive groups so the reaction can occur efficiently

20. Why is substrate orientation important?

B. It positions reactive groups so the reaction can occur efficiently

21. Enzymes can increase reaction rates by:

A. Bringing substrates close together

B. Orienting substrates properly

C. Straining bonds

D. All of the above

D. All of the above

21. Enzymes can increase reaction rates by:

A. Bringing substrates close together

B. Orienting substrates properly

C. Straining bonds

22. Which interaction could help hold a substrate in an active site?

A. Hydrogen bonds

B. Ionic interactions

C. Nonpolar interactions

D. All of the above

D. All of the above

22. Which interactions could help hold a substrate in an active site?

A. Hydrogen bonds

B. Ionic interactions

C. Nonpolar interactions

23. What happens if an amino-acid side chain in an active site becomes protonated after a major pH change?

A. Its chemical properties may change

B. Its charge can change

C. Its interactions with the substrate can change

D. All of the above

D. All of the above

23. What happens if an amino-acid side chain in an active site becomes protonated after a major pH change?

A. Its chemical properties may change

B. Its charge can change

C. Its interactions with the substrate can change

24. Why can extreme pH decrease enzyme activity?

A. It can alter amino-acid ionization and protein structure

B. It always increases substrate concentration

C. It eliminates activation energy

D. It makes every enzyme more specific

A. It can alter amino-acid ionization and protein structure

24. Why can extreme pH decrease enzyme activity?

A. It can alter amino-acid ionization and protein structure

26. The “nutcracker effect” is most closely associated with:

A. Enzyme destruction

B. Bond strain

C. DNA replication

D. Protein degradation

B. Bond strain

26. The “nutcracker effect” is most closely associated with:

B. Bond strain

27. What is chemical bond strain intended to accomplish?

A. Make a reactive bond easier to break

B. Make every bond stronger

C. Prevent catalysis

D. Destroy the active site

A. Make a reactive bond easier to break

27. What is chemical bond strain intended to accomplish?

A. Make a reactive bond easier to break

28. What is the transition state?

A. The final stable product

B. A high-energy state during a reaction

C. The enzyme after denaturation

D. The original substrate

B. A high-energy state during a reaction

28. What is the transition state?

B. A high-energy state during a reaction

A high-energy state during a reaction

transition state

29. Why is transition-state stabilization important?

A. It increases activation energy

B. It lowers the energetic barrier to the reaction

C. It prevents products from forming

D. It changes the identity of the enzyme

B. It lowers the energetic barrier to the reaction

29. Why is transition-state stabilization important?

B. It lowers the energetic barrier to the reaction

30. The oxyanion hole in chymotrypsin helps stabilize:

A. A positively charged nitrogen

B. A temporary negative charge on oxygen

C. ATP

D. DNA

B. A temporary negative charge on oxygen

30. The oxyanion hole in chymotrypsin helps stabilize:

B. A temporary negative charge on oxygen

31. The oxyanion hole commonly uses which groups to stabilize the oxyanion?

A. Protein backbone N–H groups

B. DNA phosphates

C. Lipid tails

D. Carbohydrate groups

A. Protein backbone N–H groups

31. The oxyanion hole commonly uses which groups to stabilize the oxyanion?

A. Protein backbone N–H groups

34. Which is an example of a metal-ion cofactor?

A. Mg²⁺

B. Glucose

C. DNA

D. Oxygen

A. Mg²⁺

34. Which is an example of a metal-ion cofactor?

A. Mg²⁺

35. Which is an example of an organic cofactor?

A. NAD

B. Mg²⁺

C. Zn²⁺

D. Na⁺

A. NAD

35. Which is an example of an organic cofactor?

A. NAD

37. Which statement best describes enzyme reuse?

A. Enzymes are permanently converted into products

B. Enzymes participate in catalysis but are regenerated

C. Enzymes disappear after one reaction

D. Enzymes become substrates

B. Enzymes participate in catalysis but are regenerated

38. What happens to an enzyme after product release?

A. Its active site can become available for another substrate

B. It must always be destroyed

C. It becomes DNA

D. It can never bind substrate again

A. Its active site can become available for another substrate

38. What happens to an enzyme after product release?

A. Its active site can become available for another substrate

40. Which sequence best represents the enzyme catalytic cycle?

A. Product → substrate → enzyme degradation

B. Substrate binding → induced fit → catalysis → product release

C. Enzyme destruction → substrate binding → product

D. Product binding → DNA synthesis → substrate release

B. Substrate binding → induced fit → catalysis → product release

40. Which sequence best represents the enzyme catalytic cycle?

B. Substrate binding → induced fit → catalysis → product release

42. What happens when an enzyme becomes saturated with substrate?

A. Most/all available active sites are occupied

B. No substrate is present

C. The enzyme disappears

D. Km becomes zero

A. Most/all available active sites are occupied

42. What happens when an enzyme becomes saturated with substrate?

A. Most/all available active sites are occupied

44. What does Km represent in the simplified enzyme-kinetics interpretation from the lecture?

A. Maximum enzyme concentration

B. Substrate concentration associated with ½ Vmax

C. Activation energy

D. Product concentration

B. Substrate concentration associated with ½ Vmax

44. What does Km represent in the simplified enzyme-kinetics interpretation from the lecture?

B. Substrate concentration associated with ½ Vmax

45. A lower Km generally indicates:

A. Lower apparent substrate affinity

B. Better recognition of substrate at lower concentration

C. Lower Vmax automatically

D. No substrate binding

B. Better recognition of substrate at lower concentration

45. A lower Km generally indicates:

B. Better recognition of substrate at lower concentration

46. Which enzyme has the higher apparent substrate affinity?

- Enzyme A: Km = 2 mM

- Enzyme B: Km = 10 mM

A. A

B. B

C. They are identical

D. Cannot compare

A. A

46. Which enzyme has the higher apparent substrate affinity?

- Enzyme A: Km = 2 mM

- Enzyme B: Km = 10 mM

- Enzyme A: Km = 2 mM

47. Which enzyme has the greater Vmax?

- Enzyme A: Vmax = 20 µmol/min

- Enzyme B: Vmax = 100 µmol/min

A. A

B. B

C. Both

D. Cannot determine

B. B

47. Which enzyme has the greater Vmax?

- Enzyme A: Vmax = 20 µmol/min

- Enzyme B: Vmax = 100 µmol/min

- Enzyme B: Vmax = 100 µmol/min

53. Lysozyme has an optimal pH around:

A. 1.0

B. 3.0

C. 5.2

D. 11.0

C. 5.2

53. Lysozyme has an optimal pH around:

C. 5.2

59. Which statement about enzyme catalysis is FALSE?

A. Enzymes can orient substrates

B. Enzymes can stabilize transition states

C. Enzymes change the thermodynamic ΔG of the reaction

D. Enzymes can strain substrate bonds

C. Enzymes change the thermodynamic ΔG of the reaction

The reactant that binds to an enzyme.

substrate

substrate

The reactant that binds to an enzyme.

The region where substrate binding and catalysis occur.

Active site

active site

The region where substrate binding and catalysis occur.

The energy barrier that must be overcome for a reaction to proceed.

activation energy

activation energy

The energy barrier that must be overcome for a reaction to proceed.

Describes whether a reaction is energetically favorable.

thermodynamics

thermodynamics

Describes whether a reaction is energetically favorable.

Describes how quickly a reaction occurs.

kinetics

kinetics

Describes how quickly a reaction occurs.

The thermodynamic quantity describing overall free-energy change.

ΔG

ΔG

The thermodynamic quantity describing overall free-energy change.

The enzyme model in which the enzyme changes shape around the substrate.

induced fit

induced fit

The enzyme model in which the enzyme changes shape around the substrate.

68.

The model describing complementary enzyme and substrate shapes.

lock and key model

lock and key model

The model describing complementary enzyme and substrate shapes.

69.

Destabilization of substrate bonds by the enzyme.

bond strain

bond strain

Destabilization of substrate bonds by the enzyme.