Rucete ✏ AP Biology In a Nutshell
5. Enzymes — Practice Questions
This chapter introduces enzyme structure, function, and the factors that influence enzymatic reactions.
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(Multiple Choice — Click to Reveal Answer)
1. What is the role of enzymes in chemical reactions?
(A) They increase activation energy.
(B) They decrease activation energy.
(C) They increase the free energy of products.
(D) They make endergonic reactions exergonic.
Answer
(B) — Enzymes lower the activation energy required to start a reaction.
2. What happens if an enzyme is exposed to a temperature much higher than its optimum range?
(A) It catalyzes reactions faster.
(B) It gets denatured.
(C) It becomes a competitive inhibitor.
(D) It binds permanently to its substrate.
Answer
(B) — High temperatures can denature enzymes, disrupting their shape and function.
3. Which part of an enzyme binds to the substrate?
(A) Allosteric site
(B) Binding pocket
(C) Active site
(D) Reaction chamber
Answer
(C) — The active site is the region where the substrate binds.
4. Competitive inhibitors affect enzyme action by:
(A) Binding to the allosteric site
(B) Binding to the active site
(C) Increasing activation energy
(D) Permanently deactivating enzymes
Answer
(B) — Competitive inhibitors bind to the active site, preventing substrate binding.
5. Noncompetitive inhibitors affect enzymes by:
(A) Blocking the active site
(B) Binding elsewhere and changing the enzyme’s shape
(C) Increasing the concentration of substrate
(D) Speeding up the reaction
Answer
(B) — Noncompetitive inhibitors bind to a different site, altering enzyme shape.
6. Which factor does NOT directly affect enzyme activity?
(A) Temperature
(B) pH
(C) Substrate concentration
(D) Color of the enzyme
Answer
(D) — Color is unrelated; temperature, pH, and substrate concentration affect activity.
7. Increasing the substrate concentration will:
(A) Always speed up the reaction indefinitely.(B) Speed up the reaction until the enzyme is saturated.
(C) Inhibit the reaction.
(D) Denature the enzyme.
Answer
(B) — Reaction rate increases until all active sites are saturated.
8. A catalyst functions by:
(A) Raising the energy barrier
(B) Lowering the energy barrier
(C) Supplying reactants
(D) Releasing energy to surroundings
Answer
(B) — Catalysts lower activation energy, making reactions faster.
9. Which of the following is an organic cofactor?
(A) Zinc ion
(B) NAD
(C) Calcium ion
(D) Potassium ion
Answer
(B) — NAD is an organic cofactor (coenzyme).
10. What happens during enzyme denaturation?
(A) Enzyme activity increases.
(B) The enzyme’s shape changes.
(C) Substrate concentration decreases.
(D) Energy requirements lower.
Answer
(B) — Denaturation alters the enzyme’s three-dimensional structure, affecting function.
11. What is the activation energy (EA) of a reaction?
(A) The energy of the products
(B) The energy needed to start a reaction
(C) The energy of the substrates
(D) The energy released by the reaction
Answer
(B) — Activation energy is the minimum energy required to initiate a chemical reaction.
12. Which process describes the coupling of an exergonic and an endergonic reaction?
(A) Reaction saturation
(B) Reaction equilibrium
(C) Coupled reactions
(D) Denaturation
Answer
(C) — Coupled reactions use energy released from exergonic reactions to drive endergonic reactions.
13. Which of the following can function as an enzyme?
(A) Only proteins
(B) Only carbohydrates
(C) Proteins and some RNA molecules
(D) Only lipids
Answer
(C) — Both proteins and some RNA molecules (ribozymes) can act as enzymes.
14. Which describes a competitive inhibitor?
(A) Changes enzyme shape at a distant site
(B) Blocks the active site
(C) Binds to products
(D) Binds to cofactors
Answer
(B) — Competitive inhibitors block the active site, preventing substrate binding.
15. Which of the following would most likely cause an enzyme to lose its function?
(A) Slight increase in substrate concentration
(B) Optimum temperature maintained
(C) Drastic pH change
(D) Slight decrease in enzyme concentration
Answer
(C) — Large pH changes can denature the enzyme and destroy its activity.
16. A noncompetitive inhibitor binds:
(A) To the active site
(B) To the substrate
(C) To an allosteric site
(D) To the product
Answer
(C) — Noncompetitive inhibitors bind to an allosteric site, not the active site.
17. Which vitamin is important for forming coenzymes used in respiration?
(A) Vitamin D
(B) Vitamin B
(C) Vitamin C
(D) Vitamin K
Answer
(B) — B vitamins help form NAD and other important coenzymes.
18. Enzymes speed up reactions by:
(A) Increasing the kinetic energy of substrates
(B) Raising the energy of the transition state
(C) Lowering activation energy
(D) Changing exergonic reactions into endergonic reactions
Answer
(C) — Enzymes lower the activation energy needed for reactions to occur.
19. Which reaction is energetically favorable?
(A) Endergonic
(B) Exergonic
(C) Activation
(D) Transition
Answer
(B) — Exergonic reactions release energy and are energetically favorable.
20. If a cell's enzymes are denatured, what happens?
(A) Reactions proceed faster
(B) No effect
(C) Reaction rates decrease or stop
(D) Reactions switch from exergonic to endergonic
Answer
(C) — Denatured enzymes lose their function, slowing or stopping reactions.
21. What effect does increasing substrate concentration have on enzyme activity initially?
(A) Decreases enzyme activity
(B) Increases enzyme activity
(C) Denatures the enzyme
(D) No effect at all
Answer
(B) — Initially, increasing substrate concentration increases enzyme activity until saturation.
22. What kind of reaction is represented by the breakdown of ATP into ADP and Pi?
(A) Endergonic
(B) Exergonic
(C) Coupled
(D) Inhibited
Answer
(B) — The breakdown of ATP releases energy, making it an exergonic reaction.
23. What term describes the energy difference between the reactants and the transition state?
(A) Free energy
(B) Kinetic energy
(C) Activation energy
(D) Coupled energy
Answer
(C) — Activation energy is the energy needed to reach the transition state.
24. Enzymes can lower activation energy by:
(A) Increasing reactant energy
(B) Bending substrate bonds
(C) Destroying substrates
(D) Decreasing product stability
Answer
(B) — Enzymes often bend substrate bonds to weaken them and facilitate reactions.
25. Which of the following would best demonstrate enzyme denaturation?
(A) Gradual increase in product formation
(B) Rapid rise in reaction rate
(C) Complete halt of reaction after extreme heating
(D) Higher enzyme efficiency at low temperatures
Answer
(C) — Extreme heat can denature enzymes, causing the reaction to stop.
26. In an enzyme-catalyzed reaction, what would happen if a noncompetitive inhibitor is added?
(A) The reaction rate would not change.
(B) The reaction rate would increase.
(C) The reaction rate would decrease.
(D) The enzyme would be consumed.
Answer
(C) — Noncompetitive inhibitors lower the overall reaction rate by altering the enzyme's shape.
27. Why can adding more substrate overcome the effects of a competitive inhibitor?
(A) Substrate can outcompete the inhibitor for active sites.
(B) Substrate changes the inhibitor's structure.
(C) Substrate binds to the inhibitor.
(D) Substrate prevents enzyme denaturation.
Answer
(A) — Higher substrate concentrations can outcompete competitive inhibitors at the active site.
28. What distinguishes noncompetitive inhibitors from competitive inhibitors?
(A) Noncompetitive inhibitors bind to the active site.
(B) Competitive inhibitors bind to a different site than noncompetitive inhibitors.
(C) Noncompetitive inhibitors change the enzyme’s shape.
(D) Competitive inhibitors are irreversible.
Answer
(C) — Noncompetitive inhibitors bind elsewhere and alter enzyme structure, reducing activity.
29. How do cofactors assist enzyme function?
(A) They denature the substrate.
(B) They lower activation energy directly.
(C) They help stabilize substrate binding.
(D) They supply energy to the enzyme.
Answer
(C) — Cofactors stabilize substrate binding, enhancing enzyme activity.
30. Why does enzyme activity generally increase with mild temperature increases (before denaturation)?
(A) Because it reduces activation energy to zero
(B) Because it increases kinetic energy and molecular collisions
(C) Because it denatures inhibitors
(D) Because enzymes become more rigid
Answer
(B) — Mild temperature rises increase molecular movement, leading to more frequent collisions.
31. Which of the following would NOT affect enzyme function?
(A) A drastic pH change
(B) Presence of a noncompetitive inhibitor
(C) An increase in substrate concentration beyond saturation
(D) Removing oxygen from the reaction environment
Answer
(D) — Oxygen removal affects aerobic reactions, not enzyme structure directly unless oxygen is a substrate.
32. A student measures catalase activity at different temperatures. At 50°C, the reaction rate drops sharply. Why?
(A) Catalase becomes saturated.
(B) Catalase is denatured.
(C) Substrate concentration is too high.
(D) The product inhibits catalase.
Answer
(B) — High temperatures denature enzymes like catalase, altering their active site.
33. A noncompetitive inhibitor reduces reaction rates because:
(A) It binds to the active site and blocks substrate binding.
(B) It prevents cofactors from binding.
(C) It changes the shape of the enzyme, affecting substrate binding.
(D) It permanently removes substrates.
Answer
(C) — Noncompetitive inhibitors alter enzyme shape, reducing its catalytic ability.
34. The optimum temperature for a human enzyme is most likely:
(A) 10°C
(B) 25°C
(C) 37°C
(D) 50°C
Answer
(C) — Human enzymes generally work best at body temperature, around 37°C.
35. If the 95% confidence intervals for two enzyme treatments overlap, it suggests:
(A) The treatments are statistically different.
(B) The treatments are not statistically different.
(C) There is a strong causal relationship.
(D) The treatments cannot be compared.
Answer
(B) — Overlapping confidence intervals usually suggest no statistically significant difference.
36. Describe what happens to an enzyme's structure when it becomes denatured.
Answer
The enzyme's three-dimensional structure unravels, altering the active site and preventing substrate binding.
37. Explain why increasing temperature initially speeds up an enzyme-catalyzed reaction.
Answer
Higher temperatures increase molecular collisions between enzyme and substrate, boosting reaction rates up to the optimum point.
38. Define activation energy in the context of chemical reactions.
Answer
Activation energy is the minimum energy required for reactants to reach the transition state and undergo a chemical reaction.
39. What is the main difference between competitive and noncompetitive inhibition?
Answer
Competitive inhibitors bind to the active site, while noncompetitive inhibitors bind elsewhere and change the enzyme’s shape.
40. Why does adding more substrate overcome competitive inhibition but not noncompetitive inhibition?
Answer
More substrate can outcompete competitive inhibitors at the active site, but noncompetitive inhibitors alter the enzyme’s structure, unaffected by substrate levels.
41. What happens to an enzyme-catalyzed reaction if the enzyme is exposed to a very low pH?
Answer
The enzyme may denature, losing its shape and the ability to catalyze the reaction effectively.
42. How does a coenzyme assist an enzyme during a reaction?
Answer
A coenzyme binds to the enzyme or substrate, helping to stabilize the interaction and enhance catalysis.
43. Why can't enzymes make an endergonic reaction exergonic?
Answer
Enzymes only speed up reactions by lowering activation energy; they cannot change the overall energy balance of a reaction.
44. How do competitive inhibitors slow down enzyme-catalyzed reactions?
Answer
They occupy the enzyme's active site, blocking the substrate from binding and preventing the reaction.
45. What is meant by "saturation" in enzyme activity?
Answer
Saturation occurs when all active sites of enzymes are occupied by substrates, so adding more substrate doesn't increase the reaction rate.
46. Describe the relationship between enzyme structure and function.
Answer
The specific three-dimensional shape of an enzyme determines how it interacts with its substrate; any change in structure can impair its function.
47. Why would a cell regulate enzyme activity using allosteric inhibitors?
Answer
Allosteric inhibitors allow cells to adjust enzyme activity in response to changing environmental or metabolic conditions.
48. Predict the effect of removing a necessary cofactor from an enzymatic reaction.
Answer
Removing a required cofactor would decrease or completely halt enzyme activity since the enzyme cannot function properly without it.
49. How does enzyme denaturation caused by heat differ from reversible inhibition by competitive inhibitors?
Answer
Denaturation permanently alters the enzyme’s structure, while competitive inhibition is reversible by increasing substrate concentration.
50. Explain why enzyme activity drops sharply after exceeding the optimum temperature.
Answer
Exceeding the optimum temperature denatures the enzyme, disrupting its active site and preventing substrate binding.