44) Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue
on the target protein. Many are located on the plasma membrane as integral membrane proteins or
peripheral membrane proteins. What purpose may be served by their plasma membrane localization?
A) ATP is more abundant near the plasma membrane.
B) They can more readily encounter and phosphorylate other membrane proteins.
C) Membrane localization lowers the activation energy of the phosphorylation reaction.
D) They flip back and forth across the membrane to access target proteins on either side.
E) They require phospholipids as a cofactor.
45) When you have a severe fever, what grave consequence may occur if the fever is not controlled?
A) destruction of your enzymes’ primary structure
B) removal of amine groups from your proteins
C) change in the tertiary structure of your enzymes
D) removal of the amino acids in active sites of your enzymes
E) binding of your enzymes to inappropriate substrates
46) How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
A) by binding at the active site of the enzyme
B) by changing the shape of the enzyme’s active site
C) by changing the free energy change of the reaction
D) by acting as a coenzyme for the reaction
E) by decreasing the activation energy of the reaction
47) The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the
pathway is most precisely described as
A) metabolic inhibition.
B) feedback inhibition.
C) allosteric inhibition.
D) noncooperative inhibition.
E) reversible inhibition.
48) Which of the following statements describes enzyme cooperativity?
A) A multienzyme complex contains all the enzymes of a metabolic pathway.
B) A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway.
C) A substrate molecule bound to an active site of one subunit promotes substrate binding to the active
site of other subunits.
D) Several substrate molecules can be catalyzed by the same enzyme.
E) A substrate binds to an active site and inhibits cooperation between enzymes in a pathway.
49) Allosteric enzyme regulation is usually associated with
A) lack of cooperativity.
B) feedback inhibition.
C) activating activity.
D) an enzyme with more than one subunit.
E) the need for cofactors.
50) Which of the following is an example of cooperativity?
A) the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway
B) one enzyme in a metabolic pathway passing its product to act as a substrate for the next enzyme in
the pathway
C) a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
D) the effect of increasing temperature on the rate of an enzymatic reaction
E) binding of an ATP molecule along with one of the substrate molecules in an active site
51) Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites,
whereas protein phosphatases catalyze removal of phosphate(s) from phosphorylated proteins.
Phosphorylation and dephosphorylation can function as an on-off switch for a protein’s activity, most
likely through
A) the change in a protein’s charge leading to a conformational change.
B) the change in a protein’s charge leading to cleavage.
C) a change in the optimal pH at which a reaction will occur.
D) a change in the optimal temperature at which a reaction will occur.
E) the excision of one or more peptides.
52) Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
A) cessation of cellular protein synthesis
B) localization of enzymes into specific organelles or membranes
C) exporting enzymes out of the cell
D) connecting enzymes into large aggregates
E) hydrophobic interactions
53) An important group of peripheral membrane proteins are enzymes such as the phospholipases that
cleave the head groups of phospholipids. What properties must these enzymes exhibit?
A) resistance to degradation
B) independence from cofactor interaction
C) water solubility
D) lipid solubility
E) membrane-spanning domains
54) In experimental tests of enzyme evolution, where a gene encoding an enzyme is subjected to
multiple cycles of random mutagenesis and selection for altered substrate specificity, the resulting
enzyme had multiple amino acid changes associated with altered substrate specificity. Where in the
enzyme were these amino acid changes located?
A) only in the active site
B) only in the active site or near the active site
C) in or near the active site and at surface sites away from the active site
D) only at surface sites away from the active site
E) only in the hydrophobic interior of the folded protein
55) How might an amino acid change at a site distant from the active site of the enzyme alter the
enzyme’s substrate specificity?
A) by changing the enzyme’s stability
B) by changing the enzyme’s location in the cell
C) by changing the shape of the protein
D) by changing the enzyme’s pH optimum
E) an amino acid change away from the active site cannot alter the enzyme’s substrate specificity
Art Questions
Rate of an enzyme–catalyzed reaction as a function of varying reactant
concentration, with the concentration of enzyme constant.
56) For the enzyme-catalyzed reaction shown in the figure, which of these treatments will cause the
greatest increase in the rate of the reaction, if the initial reactant concentration is 1.0 micromolar?
A) doubling the activation energy needed
B) cooling the reaction by 10°C
C) doubling the concentration of the reactants to 2.0 micromolar
D) doubling the enzyme concentration
E) increasing the concentration of reactants to 10.0 micromolar, while reducing the concentration of
enzyme by 1/2
57) In the figure, why does the reaction rate plateau at higher reactant concentrations?
A) Feedback inhibition by product occurs at high reactant concentrations.
B) Most enzyme molecules are occupied by substrate at high reactant concentrations.
C) The reaction nears equilibrium at high reactant concentrations.
D) The activation energy for the reaction increases with reactant concentration.
E) The rate of the reverse reaction increases with reactant concentration.
Activity of various enzymes at various temperatures (a) and at various pH (b).
58) Which curve(s) on the graphs may represent the temperature and pH profiles of an enzyme taken
from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70°C or higher?
A) curves 1 and 5
B) curves 2 and 4
C) curves 2 and 5
D) curves 3 and 4
E) curves 3 and 5
59) Which temperature and pH profile curves on the graphs were most likely generated from analysis of
an enzyme from a human stomach where conditions are strongly acid?
A) curves 1 and 4
B) curves 1 and 5
C) curves 2 and 4
D) curves 2 and 5
E) curves 3 and 4
The following questions are based on the reaction A + B ↔ C + D shown in Figure 8.1.
Figure 8.1
60) Which of the following terms best describes the forward reaction in Figure 8.1?
A) endergonic, ∆G > 0
B) exergonic, ∆G < 0
C) endergonic, ∆G < 0
D) exergonic, ∆G > 0
E) chemical equilibrium, ∆G = 0
61) Which of the following represents the ΔG of the reaction in Figure 8.1?
A) a
B) b
C) c
D) d
E) e
62) Which of the following in Figure 8.1 would be the same in either an enzyme-catalyzed or a
noncatalyzed reaction?
A) a
B) b
C) c
D) d
E) e
63) Which of the following represents the activation energy needed for the enzyme-catalyzed reverse
reaction, C + D → A + B, in Figure 8.1?
A) a
B) b
C) c
D) d
E) e
64) Which of the following represents the difference between the free-energy content of the reaction and
the free-energy content of the products in Figure 8.1?
A) a
B) b
C) c
D) d
E) e
65) Which of the following represents the activation energy required for the enzyme-catalyzed reaction
in Figure 8.1?
A) a
B) b
C) c
D) d
E) e
66) Which of the following represents the activation energy required for a noncatalyzed reaction in
Figure 8.1?
A) a
B) b
C) c
D) d
E) e
67) Which of the following represents the activation energy needed for the noncatalyzed reverse
reaction, C + D → A + B, in Figure 8.1?
A) a
B) b
C) c
D) d
E) e
68) Assume that the reaction in Figure 8.1 has a ΔG of -5.6 kcal/mol. Which of the following would be
true?
A) The reaction could be coupled to power an endergonic reaction with a ΔG of +6.2 kcal/mol.
B) The reaction could be coupled to power an exergonic reaction with a ΔG of +8.8 kcal/mol.
C) The reaction would result in a decrease in entropy (S) and an increase in the total energy content (H)
of the system.
D) The reaction would result in an increase in entropy (S) and a decrease in the total energy content (H)
of the system.
E) The reaction would result in products (C + D) with a greater free-energy content than in the initial
reactants (A + B).
69) Which of the following is the most correct interpretation of the figure?
A) Inorganic phosphate is created from organic phosphate.
B) Energy from catabolism can be used directly for performing cellular work.
C) ADP + i are a set of molecules that store energy for catabolism.
D) ATP is a molecule that acts as an intermediary to store energy for cellular work.
E) i acts as a shuttle molecule to move energy from ATP to ADP.
20
70) How do cells use the ATP cycle shown in the figure?
A) Cells use the cycle to recycle ADP and phosphate.
B) Cells use the cycle to recycle energy released by ATP hydrolysis.
C) Cells use the cycle to recycle ADP, phosphate, and the energy released by ATP hydrolysis.
D) Cells use the cycle to generate or consume water molecules as needed.
E) Cells use the cycle primarily to generate heat.
Scenario Questions
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by
malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase.
Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid.
71) Based on this information, which of the following is correct?
A) Succinate dehydrogenase is the enzyme, and fumarate is the substrate.
B) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate.
C) Succinate is the substrate, and fumarate is the product.
D) Fumarate is the product, and malonic acid is a noncompetitive inhibitor.
E) Malonic acid is the product, and fumarate is a competitive inhibitor.
72) What is malonic acid’s role with respect to succinate dehydrogenase?
A) It is a competitive inhibitor.
B) It blocks the binding of fumarate.
C) It is a noncompetitive inhibitor.
D) It is able to bind to succinate.
E) It is an allosteric regulator.
A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that
converts X to Y at a position remote from its active site. This binding decreases the activity of the
enzyme.
73) What is substance X?
A) a coenzyme
B) an allosteric inhibitor
C) a substrate
D) an intermediate
E) the product
74) With respect to the enzyme that converts X to Y, substance A functions as
A) a coenzyme.
B) an allosteric inhibitor.
C) the substrate.
D) an intermediate.
E) a competitive inhibitor.
End-of-Chapter Questions
The following questions are from the end-of–chapter “Test Your Understanding” section in Chapter 8 of
the textbook.
75) Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as
________ is to ________.
A) exergonic; spontaneous
B) exergonic; endergonic
C) free energy; entropy
D) work; energy
E) entropy; enthalpy
76) Most cells cannot harness heat to perform work because
A) heat is not a form of energy.
B) cells do not have much heat; they are relatively cool.
C) temperature is usually uniform throughout a cell.
D) heat can never be used to do work.
E) heat must remain constant during work.
77) Which of the following metabolic processes can occur without a net influx of energy from some
other process?
A) ADP + i → ATP + H2O
B) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
C) 6 CO2 + 6 H2O → C6H12O6 + 6 O2
D) amino acids → protein
E) glucose + fructose → sucrose
78) If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of
products is to
A) add more of the enzyme.
B) heat the solution to 90°C.
C) add more substrate.
D) add an allosteric inhibitor.
E) add a noncompetitive inhibitor.
79) Some bacteria are metabolically active in hot springs because
A) they are able to maintain a lower internal temperature.
B) high temperatures make catalysis unnecessary.
C) their enzymes have high optimal temperatures.
D) their enzymes are completely insensitive to temperature.
E) they use molecules other than proteins or RNAs as their main catalysts.
80) If an enzyme is added to a solution where its substrate and product are in equilibrium, what will
occur?
A) Additional product will be formed.
B) Additional substrate will be formed.
C) The reaction will change from endergonic to exergonic.
D) The free energy of the system will change.
E) Nothing; the reaction will stay at equilibrium.