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 6-phosphate 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
8. The standard free energy change for the hydrolysis of
ATP to ADP + Pi 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 6-phosphate, 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 enzyme-catalyzed
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 denatures.
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
14. Which of the following determines the rate of a
reaction?
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
_____________________
Exam Reviews For Students - Energy, Enzymes, and Metabolism
______________
No comments:
Post a Comment