Unit 5: Enzymes, Vitamins and Minerals - Practice Quiz

1 What is the main function of an enzyme?

2 The region of an enzyme where the substrate binds is called the:

3 According to the lock-and-key model, the active site and substrate are:

4 Many enzyme names end with which suffix?

5 Which enzyme class catalyzes oxidation-reduction reactions?

6 Enzymes that break chemical bonds by adding water belong to which class?

7 What usually happens to enzyme activity when temperature increases from a low value to the optimum temperature?

8 What may happen to an enzyme at a very high temperature?

9 The pH at which an enzyme works most effectively is called its:

10 How does increasing substrate concentration usually affect enzyme activity when enzyme concentration is fixed?

11 What does the reaction rate describe in enzyme kinetics?

12 The maximum reaction rate of an enzyme is commonly represented by:

13 In the Michaelis-Menten equation, represents:

14 When all enzyme active sites are occupied by substrate, the enzyme is described as:

15 What is enzyme inhibition?

16 A competitive inhibitor usually binds to the enzyme's:

17 A noncompetitive inhibitor usually binds to:

18 Vitamins are generally needed by the body in:

19 Which statement best describes minerals?

20 Which vitamin is commonly associated with vision and healthy skin?

21 An enzyme binds a substrate and slightly changes its shape so that the substrate fits more closely. Which model best describes this interaction?

22 How does an enzyme increase the rate of a biochemical reaction?

23 A mutation replaces an active-site amino acid that normally donates a proton during catalysis. Which consequence is most likely?

24 An enzyme transfers a phosphate group from ATP to glucose. Which enzyme class most directly describes this reaction?

25 Which enzyme class catalyzes the hydrolysis of peptide bonds using water?

26 An enzyme catalyzes the joining of two molecules using energy from ATP hydrolysis. Which class does it belong to?

27 An enzyme shows maximum activity at pH 7.0 but loses activity at pH 3.0. What is the most likely explanation?

28 Why does enzyme activity often decline sharply above the enzyme's optimum temperature?

29 If substrate concentration is increased while enzyme concentration remains constant, the reaction rate eventually reaches a plateau because:

30 Two reaction mixtures contain the same enzyme concentration, but one has twice as much enzyme substrate available. Under substrate-limited conditions, what is expected?

31 For a Michaelis-Menten enzyme, the substrate concentration equals . What fraction of is the reaction rate approximately equal to?

32 An enzyme has a lower than another enzyme for the same substrate under identical conditions. What does this generally indicate?

33 If an enzyme concentration is doubled while substrate is abundant, what change is expected in the initial reaction rate?

34 A reaction has an initial rate of micromoles per minute at a given substrate concentration. If the substrate concentration is increased far above , what rate is most likely approached?

35 A competitive inhibitor binds reversibly to the active site. Which kinetic change is expected when sufficient substrate is added?

36 An inhibitor binds only to the enzyme-substrate complex and reduces the maximum rate. Which type of inhibition best fits this description?

37 A noncompetitive inhibitor binds at a site distinct from the active site and cannot be overcome by increasing substrate concentration. What happens to ?

38 Which statement best distinguishes fat-soluble vitamins from water-soluble vitamins?

39 A person with inadequate vitamin C intake develops impaired wound healing. Which function of vitamin C is most directly related?

40 Which mineral is most directly required for hemoglobin synthesis and oxygen transport?

41 A serine protease forms a tetrahedral intermediate during peptide-bond hydrolysis. Which event most directly stabilizes the highest-energy intermediate in the reaction coordinate?

42 An enzyme accelerates a reaction by binding the transition state more tightly than either substrate or product. Which consequence is expected if a transition-state analog is introduced?

43 A mutant enzyme retains substrate binding but loses catalytic activity after replacement of a histidine residue that normally accepts a proton. Which mechanistic role was most likely disrupted?

44 An enzyme catalyzes the transfer of a phosphate group from ATP to a serine residue on a protein. Which EC class and reaction description are most appropriate?

45 Which enzyme-function pairing correctly distinguishes a lyase from a hydrolase?

46 An enzyme has maximal activity at pH 7.0, but activity decreases sharply at both pH 5 and pH 9. Which explanation best accounts for this pattern?

47 When temperature is increased over a narrow range, an enzyme's initial rate first rises and then falls abruptly. Which interpretation is most consistent with the data?

48 An enzyme displays sigmoidal velocity versus substrate concentration, and a small amount of an end product shifts the curve to the right without changing the maximal velocity. What is the most likely explanation?

49 For a Michaelis–Menten enzyme, and . What is the initial velocity at ?

50 Two enzymes have the same , but enzyme A has a lower than enzyme B for the same substrate. At substrate concentrations well below both values, which conclusion is justified?

51 An enzyme-catalyzed reaction is measured under initial-rate conditions. Doubling enzyme concentration doubles the rate, whereas doubling substrate concentration has little effect when substrate is already saturating. Which parameter is most directly demonstrated to be proportional to enzyme concentration?

52 A Lineweaver–Burk plot gives a -intercept of and an -intercept of . What are and ?

53 A mutant enzyme shows a tenfold decrease in but no change in . Which conclusion is most defensible?

54 An inhibitor increases the apparent but leaves unchanged, and its effect can be overcome by sufficiently high substrate concentration. What inhibition pattern is indicated?

55 An inhibitor binds only to the enzyme–substrate complex. Which kinetic changes are expected for ideal uncompetitive inhibition?

56 A reversible inhibitor produces intersecting Lineweaver–Burk lines on the -axis at different inhibitor concentrations. Which mechanism is most consistent with this result?

57 A drug contains a reactive group that becomes activated only after the target enzyme processes it, after which the enzyme is covalently modified. What type of inhibition is this?

58 A patient has megaloblastic anemia and neurologic dysfunction. Folate supplementation corrects the anemia but worsens the diagnostic delay. Which deficiency should be specifically investigated?

59 A person consuming a diet rich in plant-based iron develops iron deficiency despite adequate total iron intake. Which physiological factor most plausibly contributes?

60 Which combination best explains why vitamin C deficiency can impair connective tissue integrity and also contribute to anemia?