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6
Energy, Enzymes, and Metabolism
TEST FILE QUESTIONS
Fill in the Blank
1. Cells cannot create energy because _______.
Answer: energy cannot be created or destroyed
2. Variations of enzymes that allow organisms to adapt to changing environments are
termed _______.
Answer: isozymes
3. Although some enzymes consist entirely of one or more polypeptide chains, others
possess a tightly bound nonprotein portion called a _______.
Answer: prosthetic group
4. Cells mostly use _______ as an immediate source of energy to drive reactions.
Answer: ATP
5. A _______ reaction, in which one reaction is used to drive another, is the major means
of carrying out energy-requiring reactions within cells.
Answer: coupled
6. The second law of thermodynamics states that the _______, or disorder, of the
universe is constantly increasing.
Answer: entropy
7. When a drop of ink is added to a beaker of water, the dye molecules become randomly
dispersed throughout the water. This is an example of an increase in _______.
Answer: entropy
8. For a reaction to be spontaneous, the change in free energy of the reaction, ∆G, must
be _______.
Answer: negative
9. The enzyme phosphoglucoisomerase catalyzes the conversion of glucose 6-phosphate
to fructose 6-phosphate. The region on phosphoglucoisomerase where glucose 6phosphate binds is called the _______.
Answer: active site
10. The ∆G of a spontaneous reaction is negative, indicating that the reaction releases
free energy. Such a reaction is _______.
Answer: exergonic
11. Enzymes are biological _______.
Answer: catalysts
12. The zinc ion in the active site of the enzyme thermolysin is called a _______.
Answer: prosthetic group
13. When an enzyme is heated until its three-dimensional structure is destroyed, the
enzyme is said to be
Answer: denatured
14. The temperature of water above a waterfall is probably _______ than the temperature
where the water falls.
Answer: colder
15. _______ is the term used for all the chemical activity of a living organism.
Answer: Metabolism
16. Heat, light, electricity, and motion are all examples of _______ energy.
Answer: kinetic
17. The energy in a system that exists due to position is _______ energy.
Answer: potential
18. Potential energy can be converted to _______ energy, which does work.
Answer: kinetic
19. The building up of molecules in a living system is _______; the breaking down of
molecules in a living system is _______.
Answer: anabolism; catabolism
20. The first law of thermodynamics is that _______.
Answer: energy is neither created nor destroyed
Multiple Choice
1. Water held back by a dam represents what kind of energy?
a. Hydroelectric
b. Irrigation
c. Potential
d. Kinetic
e. At times, all of the above
Answer: c
2. The change in free energy is related to a
a. change in heat.
b. change in entropy.
c. change in pressure.
d. Both a and b
e. a, b, and c
Answer: d
3. Enzymes are sensitive to
a. temperature.
b. pH.
c. irreversible inhibitors such as DIPF.
d. allosteric effectors.
e. All of the above
Answer: e
4. End products of biosynthetic pathways often act to block the initial step in that
pathway. This phenomenon is called
a. allosteric inhibition.
b. denaturation.
c. branch pathway inhibition.
d. feedback inhibition.
e. binary inhibition.
Answer: d
5. Which of the following identifies a group of enzymes that is important in fine-tuning
the metabolic activities of cells?
a. Isozymes
b. Alloenzymes
c. Allosteric enzymes
d. Both a and c
e. a, b, and c
Answer: d
6 Competitive and noncompetitive enzyme inhibitors differ with respect to
a. the precise location on the enzyme to which they bind.
b. their pH.
c. their binding affinities.
d. their energies of activation.
e. None of the above
Answer: a
7. During photosynthesis, plants use light energy to synthesize glucose from carbon
dioxide. However, plants do not use up energy during photosynthesis; they merely convert it from light energy to chemical energy. This is an illustration of
a. increasing entropy.
b. chemical equilibrium.
c. the first law of thermodynamics.
d. the second law of thermodynamics.
e. a spontaneous reaction.
Answer: c
i
is –7.3
kcal/mol. What can you conclude from this information?
a. The reaction will never reach equilibrium.
b. The free energy of ADP and phosphate is higher than the free energy of ATP.
c. The reaction requires energy.
d. The reaction is endergonic.
e. The reaction is exergonic.
Answer: e
9. The hydrolysis of maltose to glucose is an exergonic reaction. Which of the following
statements is true?
a. The reaction requires the input of free energy.
b. The free energy of glucose is larger than the free energy of maltose.
c. The reaction is not spontaneous.
d. The reaction releases free energy.
e. At equilibrium, the concentration of maltose is higher than the concentration of
glucose.
Answer: d
10. The first law of thermodynamics states that the total energy in the universe is
a. decreasing.
b. increasing.
c. constant.
d. being converted to free energy.
e. being converted to matter.
Answer: c
11. If the enzyme phosphohexosisomerase is added to a 0.3 M solution of fructose 6phosphate, and the reaction is allowed to proceed to equilibrium, the final concentrations
are 0.2 M glucose 6-phosphate and 0.1 M fructose 6-phosphate. These data give an
equilibrium constant of 2. What is the equilibrium constant if the initial concentration of
fructose 6-phosphate is 3 M?
a. 2
b. 3
c. 5
d. 10
e. 20
Answer: a
12. You are studying the effects of temperature on the rate of a particular enzymecatalyzed reaction. When you increase the temperature from 40°C to 70°C, what effect
will this have on the rate of the reaction?
a. It will increase.
b. It will decrease.
c. It will decrease to zero because the enzyme
d. It will increase and then decrease.
e. This cannot be answered without more information.
Answer: e
13. If ∆G of a chemical reaction is negative and the change in entropy is positive, what
can you conclude about the reaction?
a. It requires energy.
b. It is endergonic.
c. It is exergonic.
d. It will not reach equilibrium.
e. It decreases the disorder in the system.
Answer: c
a. ∆S
b. ∆G
c. ∆H
d. The activation energy
e. The overall change in free energy
Answer: d
15. In a chemical reaction, transition-state species have free energies
a. lower than either the reactants or the products.
b. higher than either the reactants or the products.
c. lower than the reactants, but higher than the products.
d. higher than the reactants, but lower than the products.
e. lower than the reactants, but the same as the products.
Answer: b
16. The hydrolysis of sucrose to glucose and fructose is exergonic. However, if you
dissolve sucrose in water and keep the solution overnight at room temperature, there is no
detectable conversion to glucose and fructose. Why?
a. The change in free energy of the reaction is positive.
b. The activation energy of the reaction is high.
c. The change in free energy of the reaction is negative.
d. This is a condensation reaction.
e. The free energy of the products is higher than the free energy of the reactants.
Answer: b
17. The enzyme α-amylase increases the rate at which starch is broken down into smaller
oligosaccharides. It does this by
a. decreasing the equilibrium constant of the reaction.
b. increasing the change in free energy of the reaction.
c. decreasing the change in free energy of the reaction.
d. increasing the change in entropy of the reaction.
e. lowering the activation energy of the reaction.
Answer: e
18. The enzyme glyceraldehyde 3-phosphate dehydrogenase catalyzes the reaction
glyceraldehyde 3-phosphate → 1,3-diphosphoglycerate. The region of the enzyme where
glyceraldehyde 3-phosphate binds is called the
a. transition state.
b. groove.
c. catalyst.
d. active site.
e. energy barrier.
Answer: d
19. The enzyme glucose oxidase binds the six-carbon sugar glucose and catalyzes its
conversion to glucono-1,4-actone. Mannose is also a six-carbon sugar, but glucose
oxidase cannot bind mannose. The specificity of glucose oxidase is based on the
a. free energy of the transition state.
b. activation energy of the reaction.
c. change in free energy of the reaction.
d. three-dimensional shape and structure of the active site.
e. rate constant of the reaction.
Answer: d
20. In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to
ethanol increases as you increase the concentration of acetaldehyde. Eventually, the rate
of the reaction reaches a maximum, at which point further increases in the concentration
of acetaldehyde have no effect. Why?
a. All of the alcohol dehydrogenase molecules are bound to acetaldehyde molecules.
b. At high concentrations of acetaldehyde, the activation energy of the reaction increases.
c. At high concentrations of acetaldehyde, the activation energy of the reaction decreases.
d. The enzyme is no longer specific for acetaldehyde.
e. At high concentrations of acetaldehyde, the change in free energy of the reaction
decreases.
Answer: a
21. When an enzyme catalyzes both an exergonic reaction and an endergonic reaction,
the two reactions are said to be
a. substrates.
b. endergonic.
c. kinetic.
d. activated.
e. coupled.
Answer: e
22. In glycolysis, the exergonic reaction 1,3-diphosphoglycerate → 3-phosphoglycerate is
coupled to the reaction ADP + Pi → ATP. Which of the following is most likely to be
true about the reaction ADP + Pi →ATP?
a. The reaction never reaches equilibrium.
b. The reaction is spontaneous.
c. There is a large decrease in free energy.
d. The reaction is endergonic.
e. Temperature will not affect the rate constant of the reaction.
Answer: d
23. Trypsin and elastase are both enzymes that catalyze hydrolysis of peptide bonds. But
trypsin only cuts next to lysine and elastase only cuts next to alanine. Why?
a. Trypsin is a protein, and elastase is not.
b. ∆G for the two reactions is different.
c. The shape of the active site for the two enzymes is different.
d. One of the reactions is endergonic, and the other is exergonic.
e. Hydrolysis of lysine bonds requires water; hydrolysis of alanine bonds does not.
Answer: c
24. The enzyme catalase has a ferric ion tightly bound to the active site. The ferric ion is
called a(n)
a. side chain.
b. enzyme.
c. coupled reaction.
d. prosthetic group.
e. substrate.
Answer: d
25. The addition of the competitive inhibitor mevinolin slows the reaction HMG-CoA →
mevalonate, which is catalyzed by the enzyme HMG-CoA reductase. How could you
overcome the effects of mevinolin and increase the rate of the reaction?
a. Add more mevalonate
b. Add more HMG-CoA
c. Lower the temperature of the reaction
d. Add a prosthetic group
e. Lower the rate constant of the reaction
Answer: b
26. How does a noncompetitive inhibitor inhibit binding of a substrate to an enzyme?
a. It binds to the substrate.
b. It binds to the active site.
c. It lowers the activation energy.
d. It increases the ∆G of the reaction.
e. It changes the shape of the active site.
Answer: e
27. Which type of inhibitor can be overcome completely by the addition of more
substrate?
a. Irreversible
b. Noncompetitive
c. Competitive
d. Prosthetic
e. Isotonic
Answer: c
28. Binding of substrate to the active site of an enzyme is
a. reversible.
b. irreversible.
c. noncompetitive.
d. coupled.
e. allosteric.
Answer: a
29–30. Consider the following metabolic pathway. Reactants and products are designated
by capital letters; enzymes are designated by numbers.
29. Which enzyme is end product G most likely to inhibit?
a. 1
b. 2
c. 3
d. 5
e. 6
Answer: d
30. Assume that end product E is a negative feedback regulator of enzyme
1. What happens to a cell when it is grown in the presence of large amounts of E?
a. The cell can’t make G.
b. The cell can’t make A.
c. The cell makes too much G.
d. The cell makes too much E.
e. The cell makes too much D.
Answer: a
31. An allosteric inhibitor
a. decreases the concentration of inactive enzyme.
b. decreases the concentration of active enzyme.
c. increases the concentration of product.
d. decreases the concentration of substrate.
e. increases the concentration of enzyme–substrate complex.
Answer: b
32. An RNA molecule that has enzyme activity is called
a. RNAse.
b. ribonuclease.
c. an allosteric enzyme.
d. a regulatory enzyme.
e. a ribozyme.
Answer: e
33. The presence in a system of energy that is unusable for the purpose of doing work is
related to the system’s
a. temperature.
b. entropy.
c. work.
d. thermodynamics.
e. equilibrium.
Answer: b
34. The molecules that are acted on by an enzyme are called
a. products.
b. substrates.
c. carriers.
d. prosthetics.
e. effectors.
Answer: b
35. The sum total of all the chemical reactions in a living structure is called its
a. energetics.
b. activity.
c. digestive power.
d. entropy.
e. metabolism.
Answer: e
36. The rate of a chemical reaction in a cell is the measure of how
a. often the reaction occurs.
b. quickly the reaction reaches equilibrium.
c. much energy must be added to have the reaction occur.
d. much activation energy is required to have the reaction occur.
e. easily the reaction is inhibited.
Answer: b
37. The statement “Enzymes are highly specific” means that certain
a. enzymes are found in certain cells.
b. reactions involving certain substrates are catalyzed by certain enzymes.
c. enzymes require certain concentrations of substrates.
d. reactions with certain activation energies are catalyzed by certain enzymes.
e. concentrations of substrates work with certain enzymes.
Answer: b
38. An active site is
a. the part of the substrate that binds with an enzyme.
b. the part of the enzyme that binds with a substrate.
c. the site where energy is added to an enzyme catalyst.
d. the site where enzymes are found in cells.
e. None of the above
Answer: b
39. Enzymatic reactions can become saturated as substrate concentration increases
because
a. enzymes have the maximum possible number of hydrogen atoms attached to them.
b. the concentration of substrate cannot increase any higher.
c. substrates are inhibitors of enzymes.
d. the activation energy of the reaction cannot be further lowered.
e. there are a limited number of the enzyme molecules present.
Answer: e
40. Competitive inhibitors of enzymes work by
a. fitting into the active site.
b. fitting into a site other than the active site.
c. altering the shape of the enzyme.
d. changing the enzyme into an inactive form.
e. increasing the activation energy of the enzyme-catalyzed reaction.
Answer: a
41. Allosteric inhibitors act by
a. decreasing the amount of enzyme molecules.
b. increasing the amount of enzyme molecules.
c. decreasing the amount of the inactive form of the enzyme.
d. decreasing the amount of the active form of the enzyme.
e. increasing the amounts of substrate.
Answer: d
42. Negative feedback in a sequence of chemical reactions involves a chemical that
appears
a. late in the sequence and inhibits an earlier reaction.
b. early in the sequence and inhibits a later reaction.
c. early in the sequence and activates a later reaction.
d. late in the sequence and activates an earlier reaction.
e. late in the sequence and inhibits a later reaction.
Answer: a
43. Denatured enzymes are the same as
a. ribozymes.
b. abzymes.
c. isozymes.
d. destroyed enzymes.
e. coenzymes.
Answer: d
44. The inhibition of enzyme activity by noncompetitive inhibitors can be reduced
a. by decreasing the concentration of allosteric enzymes.
b. by decreasing the concentration of substrate.
c. by increasing the concentration a competitive inhibitor.
d. by increasing the concentration of substrate.
e. only when they become unbound.
Answer: e
45. The concentration of a substrate in a reaction at equilibrium depends most strongly on
the concentration(s) of
a. enzyme.
b. the active form of the enzyme.
c. the activator.
d. the other substrates and products.
e. the products.
Answer: e
46. An allosteric site of an enzyme is the place where a(n) _______ may bind.
a. competitive inhibitor
b. substrate
c. prosthetic group
d. activator
e. coenzyme
Answer: d
47. In some cases, a substrate–enzyme complex is stabilized by
a. hydrogen bonds.
b. covalent bonds.
c. ionic attractions.
d. hydrophobic interactions.
e. All of the above
Answer: e
48. Once a spontaneous reaction is initiated, the speed with which it reaches equilibrium
without a catalyst is influenced by
a. the equilibrium constant.
b. a change in free energy.
c. a change in entropy.
d. activation energy.
e. standard free energy change.
Answer: b
49. Factors that can either activate or inhibit allosteric enzymes are called
a. proteins.
b. coenzymes.
c. sites.
d. effectors.
e. competitors.
Answer: d
50. The diversity of chemical reactions occurring in a cell depends mostly on which
molecules in the cell?
a. Isozymes
b. Coenzymes
c. Ribozymes
d. Abzymes
e. Enzymes
Answer: e
51. When organisms move from one environment to another, they sometimes synthesize
variations of existing enzymes, which are called
a. coenzymes.
b. abzymes.
c. isozymes.
d. effectors.
e. activators.
Answer: c
52 A type of enzyme inhibitor that binds within the enzyme’s active site is termed
a. allosteric.
b. noncompetitive.
c. competitive.
d. extracompetitive.
e. None of the above
Answer: c
53. The catalysis mechanism used by lysozyme is
a. acid-base catalysis.
b. covalent catalysis.
c. metal cofactor redox catalysis.
d. induced strain.
e. unknown.
Answer: d
54. The ability of an enzyme’s active site to sometimes bind inhibitors that are larger than
the substrate is called
a. induced fit.
b. enzyme flex.
c. the lock and key paradox.
d. substrate-induced active site shaping.
e. enzyme retrofit.
Answer: a
55. The process that involves an end product acting as an inhibitor of an earlier step in a
metabolic pathway is called
a. feedback activation.
b. feedback inhibition.
c. positive feedback.
d. concerted activation.
e. competitive inhibition.
Answer: b
56. What can never be created or destroyed?
a. Entropy
b. Energy
c. Free energy
d. Thermal energy
e. Potential energy
Answer: b
57. The maximum possible rate of an enzyme reaction influenced by a competitive
inhibitor depends on the concentration of
a. inhibitor.
b. substrate.
c. product.
d. enzyme.
e. free energy.
Answer: b
58. Enzymes of the acid-base catalysis type contain
a. a metal ion bound to a side chain.
b. a prosthetic group.
c. a coenzyme.
d. an acid or base amino acid residue in the active site.
e. a covalent-activated active site.
Answer: d
59. Which of the following is true regarding allosteric regulators?
a. Positive regulators stabilize the active form of the enzyme.
b. All enzymes are allosterically regulated.
c. Enzymes that are allosterically regulated are made of multiple polypeptide subunits.
d. Both the active site and the regulatory site are present on the same subunit.
e. Allosteric regulators bind to the active site, blocking enzyme function.
Answer: a
60. When ATP loses a phosphate to form ADP,
a. free energy is released by the loss of a phosphate.
b. energy is consumed.
c. the reaction ends.
d. chemical energy is converted to light energy.
e. ribose loses an oxygen to become deoxyribose.
Answer: a
61. Fireflies
a. release a considerable amount of energy as heat.
b. light up to signal danger.
c. use ATP to begin luciferin oxidation.
d. are constantly converting light energy into chemical energy.
e. have a short life cycle due to rapid depletion of ATP.
Answer: c
62. How does the second law of thermodynamics apply to organisms?
a. As energy transformations occur, free energy increases and unusable energy decreases.
b. To maintain order, life requires a constant input of energy.
c. The potential energy of ATP is converted to kinetic energy such as muscle
contractions.
d. Reactions occur only with an input of energy.
e. It doesn’t; the complexity of organisms is in disagreement with the second law.
Answer: b
63. Which of the following is true of ATP?
a. The hydrolysis of ATO is exergonic.
b. ATP consists of adenine bonded to deoxyribose.
c. ATP releases a relatively small amount of energy when hydrolyzed.
d. An active cell requires a hundred or so molecules of ATP per second.
e. On average, ATP is consumed within a second of its formation.
Answer: e
64. Aspirin reduces swelling and pain by
a. adding hydroxyl groups to amino acids.
b. hindering the conversion of linear fatty acids to a ring structure.
c. blocking a substrate’s access to enzymes.
d. accelerating the formation of a fatty acid ring structure.
e. repairing damage to the stomach wall and aiding in blood clotting.
Answer: b
65. Prescription drugs are designed to
a. block specific chemical transformations by inhibiting specific enzymes.
b. break chemical bonds, thereby inhibiting metabolism.
c. phosphorylate many different molecules.
d. block the energy coupling cycle of ATP.
e. block acetylcholinesterase and subsequent nerve impulse transmission.
Answer: a
66. Which of the following statements about enzymes is false?
a. An enzyme changes shape when it binds to a substrate.
b. Enzymes lower the activation energy.
c. Enzymes are highly specific.
d. An enzyme may orient substrates, induce strain, or temporarily add chemical groups.
e. Most enzymes are much smaller than their substrates.
Answer: e
67. The enzyme sucrase increases the rate at which sucrose is broken down into glucose
and fructose. Sucrase works by
a. increasing the amount of free energy of the reaction.
b. lowering the activation energy of the reaction.
c. decreasing the equilibrium constant of the reaction.
d. supplying energy to speed up the reaction.
e. changing the shape of the active site.
Answer: b
68. Enzymes are highly sensitive to pH and temperature because
a. changes in the environment raise their activation energy.
b. changes in temperature and pH readily break their hydrogen bonds.
c. of their three-dimensional structure and side chains.
d. at extreme temperatures and pH levels, coenzymes add chemical groups to the
substrate.
e. extremes of temperature and pH level change the ionization rate.
Answer: c
69. How do competitive and noncompetitive enzyme inhibitors differ?
a. Competitive inhibitors bind to the active site, whereas noncompetitive inhibitors
change the shape of the active site.
b. Competitive inhibitors have a higher energy of activation than noncompetitive
inhibitors have.
c. They function at different pH values.
d. Noncompetitive enzyme inhibitors contain magnesium, whereas competitive inhibitors
contain iron.
e. Noncompetitive enzyme inhibitors are reversible, whereas competitive inhibitors are
irreversible.
Answer: a
STUDY GUIDE QUESTIONS
Knowledge and Synthesis Questions
1. ATP is necessary for the conversion of glucose to glucose 6-phosphate. Splitting ATP
into ADP and Pi releases energy into what form?
a. Potential
b. Kinetic
c. Entropic
d. Enthalpic
2. Before ATP is split into ADP and Pi it holds what type of energy?
a. Potential
b. Kinetic
c. Entropic
d. Enthalpic
3. Which of the following statements concerning energy transformations is true?
a. Increases in entropy reduce usable energy.
b. Energy may be created during transformation.
c. Potential energy increases with each transformation.
d. Increases in temperature decrease total amount of energy available.
4. A reaction has a ΔG of –20kcal/mole. This reaction is
a. endergonic, and equilibrium is far toward completion.
b. exergonic, and equilibrium is far toward completion.
c. endergonic, and the forward reaction occurs at the same rate as the reverse reaction.
d. exergonic, and the forward reaction occurs at the same rate as the reverse reaction.
5. ATP hydrolysis releases energy to fuel cellular functions. ATP hydrolysis is
a. endergonic.
b. exergonic.
c. chemoautotrophic.
d. None of the above
6. Enzymes are biological catalysts and function by
a. increasing free energy in a system.
b. lowering activation energy of a reaction.
c. lowering entropy in a system.
d. increasing temperature near a reaction.
7. Which of the following contribute to the specificity of enzymes.
a. Each enzyme has a narrow range of temperature and pH optima.
b. Each enzyme has a specific active site that interacts with a particular substrate.
c. Substrates themselves may alter the active site slightly for optimum catalysis.
d. All of the above
8. Coenzymes and cofactors as well as prosthetic groups assist enzyme function by
a. stabilizing three-dimensional shape and maintaining active sites.
b. assisting with the binding of enzyme and substrate.
c. Both a and b
d. None of the above
9. Which of the following are characteristics of enzymes?
a. They are not consumed by the enzyme-mediated reaction.
b. They are not altered by the enzyme-mediated reaction.
c. They lower activation energy.
d. All of the above
10. Ascorbic acid, found in citrus fruits, acts as an inhibitor to catecholase, the enzyme
responsible for the browning reaction in fruits such as apples, peaches, and pears. One
possibility for its function could be that ascorbic acid is very similar in size and shape to
catechol, the substrate of the browning reaction. If this is true, then this inhibition is most
likely an example of __________ inhibition.
a. indirect
b. competitive
c. noncompetitive
d. none of the above
11. Refer to question 10. Suppose further studies indicate that ascorbic acid is not similar
to catechol in size and shape but that the pH of the ascorbic acid solution is denaturing
catecholase. If this is true, then this inhibition is most likely an example of __________
inhibition.
a. competitive
b. irreversible
c. noncompetitive
d. none of the above
12. Metabolism is organized into pathways. The pathway is linked in which of the
following manners?
a. All cellular functions feed into a central pathway.
b. All steps in the pathway are catalyzed by the same enzyme.
c. The product of one step in the pathway functions as the substrate in the next step.
d. Products of the pathway accumulate and are secreted from the cell.
13. Which of the following represents an enzyme-catalyzed reaction?
a. E + P → E + S
b. E + S → E + P
c. E + S → P
d. E + S → E
14. Which of the following graphs of enzyme-mediated reactions represents an allosteric
enzyme?
a.
b.
c.
Answers
Knowledge and Synthesis Answers
1. b. The released energy is available to do work; therefore, it is kinetic energy.
2. a. Potential energy is energy held within chemical bonds that may be converted to
working kinetic energy.
3. a. Total energy = Free energy + entropy × temperature. Any increase in entropy is
necessarily going to reduce free energy.
4. b. A negative ΔG indicates an exergonic reaction with energy being liberated. A large
ΔG indicates that equilibrium lies toward completion.
5. b. ATP hydrolysis is exergonic, resulting in a ΔG of –12 kcal/mol.
6. b. Enzymes reduce activation energy and speed up reactions.
7. d. Enzymes are specific to particular substrates that may actually “adjust” the fit of the
active site. They also function in specific, narrow optimum ranges of pH and temperature.
8. c. Cofactors, coenzymes, and prosthetic groups assist with the maintenance of an
enzyme’s three-dimensional shape and the conformation of the active site.
9. d. Enzymes are not consumed or altered in any way during an enzyme-mediated
reaction, and they function to lower the activation energy of a reaction.
10. b. Competitive inhibitors compete for the active site with the substrate.
11. b. Denaturing an enzyme alters its three-dimensional structure, often irreversibly.
12. c. Within a given pathway, the products of the preceding step act as substrates for
subsequent steps.
13. b. Substrate is converted to product and the enzyme is unchanged.
14. b. Allosteric enzymes produce sigmoid curves on reaction rate graphs. See Figure
6.20b.
TEXTBOOK SELF QUIZ QUESTIONS
Self-Quiz
1. Coenzymes differ from enzymes in that coenzymes are
a. only active outside the cell.
b. polymers of amino acids.
c. smaller, such as vitamins.
d. specific for one reaction.
e. always carriers of high-energy phosphate.
2. Which statement about thermodynamics is true?
a. Free energy is used up in an exergonic reaction.
b. Free energy cannot be used to do work, such as chemical transformations.
c. The total amount of energy can change after a chemical transformation.
d. Free energy can be kinetic but not potential energy
e. Entropy tends always to a maximum.
3. In a chemical reaction,
a. the rate depends on the value of ΔG.
b. the rate depends on the activation energy.
c. the entropy change depends on the activation energy.
d. the activation energy depends on the value of ΔG.
e. the change in free energy depends on the activation energy.
4. Which statement about enzymes is not true?
a. They consist of proteins, with or without a nonprotein part.
b. They change the rate of the catalyzed reaction.
c. They change the value of ΔG of the reaction.
d. They are sensitive to heat.
e. They are sensitive to pH.
5. The active site of an enzyme
a. never changes shape.
b. forms no chemical bonds with substrates.
c. determines, by its structure, the specificity of the enzyme.
d. looks like a lump projecting from the surface of the enzyme.
e. changes ΔG of the reaction.
6. The molecule ATP is
a. a component of most proteins.
b. high in energy because of the presence of adenine (A).
c. required for many energy-producing biochemical reactions.
d. a catalyst.
e. used in some endergonic reactions to provide energy.
7. In an enzyme-catalyzed reaction,
a. a substrate does not change.
b. the rate decreases as substrate concentration increases.
c. the enzyme can be permanently changed.
d. strain may be added to a substrate.
e. the rate is not affected by substrate concentration.
8. Which statement about enzyme inhibitors is not true?
a. A competitive inhibitor binds the active site of the enzyme.
b. An allosteric inhibitor binds a site on the active form of the enzyme.
c. A noncompetitive inhibitor binds a site other than the active site.
d. Noncompetitive inhibition cannot be completely overcome by the addition of more
substrate.
e. Competitive inhibition can be completely overcome by the addition of more substrate.
9. Which statement about feedback inhibition of enzymes is not true?
a. It is exerted through allosteric effects.
b. It is directed at the enzyme that catalyzes the first committed step in a branch of a
pathway.
c. It affects the rate of reaction, not the concentration of enzyme.
d. It acts very slowly.
e. It is an example of negative feedback.
10. Which statement about temperature effects is not true?
a. Raising the temperature may reduce the activity of an enzyme.
b. Raising the temperature may increase the activity of an enzyme.
c. Raising the temperature may denature an enzyme.
d. Some enzymes are stable at the boiling point of water.
e. All enzymes have the same optimal temperature.
Answers
1. c
2. e
3. b
4. c
5. c
6. e
7. d
8. b
9. a
10. e
ONLINE QUIZ QUESTIONS
1.The overall reaction: glucose + O2 + CO2 + H2O + energy
a.can occur in biological systems without enzymes.
b.is endergonic.
c.is exergonic.
d.occurs in a single step in cells.
e.transforms glucose molecules to a higher energy state.
Answer: c
2.Which statement about thermodynamics is not true?
a.Free energy is given off in an exergonic reaction.
b.Free energy can be used to do work.
c.A spontaneous reaction is exergonic.
d.Free energy tends always to a minimum.
e.Entropy tends always to a minimum.
Answer: e
3.Which of the following statements about energy is true?
a.All molecules have the same energy content.
b.ADP has more energy than ATP.
c.Oxidized compounds have more free energy than reduced compounds.
d.Reduced compounds have more free energy than oxidized compounds.
e.Substances capable of oxidation require ATP hydrolysis.
Answer: d
4.Which statement about kinetic energy is true?
a.It is stored energy.
b.It is the energy of movement.
c.It does not alter the state or motion of matter.
d.Water stored behind a dam is an example.
e.It can be stored in chemical bonds.
Answer: b
5.Which of the following is not part of the second law of thermodynamics?
a.When energy is converted from one form to another, some of that energy becomes
unavailable to do work.
b.Not all energy can be used.
c.If needed free energy is not available, the reaction does not occur.
d.As a result of energy conversions, disorder tends to increase.
e.The total energy before the transformation equals the total energy after the
transformation.
Answer: e
6.Which of the following is a characteristic of a coenzyme?
a.Coenzymes contain inorganic ions.
b.Coenzymes are usually larger than the enzyme to which they bind.
c.Coenzymes are permanently bound to the enzyme.
d.Coenzymes must collide with the enzyme to bind to its active site.
e.Coenzymes include the heme group that is attached to the oxygen-carrying protein in
hemoglobin.
Answer: d
7.The rate of an enzyme-catalyzed reaction
a.is constant under all conditions.
b.decreases as substrate concentration increases.
c.cannot be measured.
d.can be affected by the pH of the environment.
e.can be increased by inhibitors.
Answer: d
8.Which statement about ATP is not true?
a.ATP gains and transfers free energy needed by the cell to do work.
b.ATP can be converted into a building block for DNA and RNA.
c.The hydrolysis of ATP is endergonic and yields ADP.
d.ATP can phosphorylate.
e.ATP consists of adenine bonded to ribose, which is attached to three phosphate groups.
Answer: c
9.Which statement about irreversible inhibition of enzymes is true?
a.The inhibitor can bind non-covalently to the enzyme’s active site.
b.Inhibitors are classified as either competitive or non-competitive.
c.The inhibitor can create a covalent bond and permanently inactivate the enzyme.
d.The inhibitor and substrate compete since only one can bind to the active site.
e.The inhibitor may bind to a site away from the active site and change the enzyme’s
shape.
Answer: c
10.Which statement about pH effects on enzyme activity is not true?
a.Decreasing or increasing pH from optimum may reduce the activity of an enzyme.
b.Most biochemical reactions have an optimum pH range.
c.If a pH change occurs, the enzyme may no longer have the correct shape to bind to its
substrate.
d.In neutral or acidic solutions, carboxyl groups release H+ and become negatively
charged carboxylate groups.
e.In neutral or acidic solutions, amino groups accept H+ and become positively charged
ammonium groups.
Answer: d
11.Enzymes are
a. biological catalysts that bind specific reactant molecules.
b. a type of protein.
c. catalysts that lower the activation energy of a reaction.
d. All of the above.
e. None of the above.
Answer: d
12.Which of the following statements concerning enzymes is true?
a. Molecular structure does not determine enzyme function.
b. Binding at the active site allows the enzyme to always retain its shape.
c. Enzymes function on their own; they never need cofactors or any sort of regulation.
d. Some enzymes change shape when substrate binds to them.
e. Non-competitive inhibitors compete for the active site.
Answer: d
13.Which of the following statements concerning enzymes is false?
a. In the absence of an enzyme, the two types of substrate molecules react very slowly.
b. Enzymes speed up the rate of a chemical reaction.
c. The active site of an enzyme holds the substrate molecules in the correct orientation,
which increases the opportunity to form products.
d. Non-competitive inhibitors increase the rate of an enzyme-catalyzed reaction.
e. A competitive inhibitor binds at the active site.
Answer: d
14.The optimal temperature of all enzymes in a single organism falls within a small
range.
a. true
b. false
Answer: a