Chapter 8 Enzymes: Basic Concepts and Kinetics

Multiple-Choice Questions

1) The site on an enzyme where the reaction that is catalyzed by the enzyme occurs is the
_____.

A) binding site
B) substrate site
C) allosteric site
D) regulatory site
E) active site

Answer: E
Section: Introduction

2) What term describes the substance that is bound by an enzyme and converted to product?

A) inhibitor
B) substrate
C) coenzyme
D) prosthetic group
E) cofactor

Answer: B
Section: 8.1

3) What term describes an enzyme without its required cofactor?

A) holoenzyme
B) coenzyme
C) isozyme
D) apoenzyme
E) None of the answers is correct.

Answer: D
Section: 8.1

4) A tightly bound cofactor for an enzyme is often called a(n) _____.

A) prosthetic group
B) coenzyme
C) allosteric activator
D) inorganic cofactor
E) None of the answers is correct.

Answer: A
Section: 8.1

5) If a reaction is exergonic at specific reactant concentrations, it is considered _____.

A) at equilibrium
B) nonspontaneous
C) spontaneous
D) irreversible
E) None of the answers is correct.

Answer: C
Section: 8.2

6) A(n) _____ requires an input of energy to proceed.

A) reaction at equilibrium
B) irreversible reaction
C) spontaneous reaction
D) exergonic reaction
E) endergonic reaction

Answer: E
Section: 8.2

7) The kcat is often referred to as the _____.

A) turnover number
B) Michaelis constant
C) dissociation constant
D) rate constant
E) None of the answers is correct.

Answer: A
Section: 8.4

8) The Circe effect enhances what aspect of enzyme catalysis?

A) catalysis of substrate to product

B) binding of substrate
C) removal of product(s) from active site
D) prevention of enzyme inhibition
E) None of the answers is correct.

Answer: B
Section: 8.4

9) What type of enzymes often display sigmoidal plots of activity versus substrate
concentration?

A) holoenzymes
B) monomeric enzymes
C) allosteric enzymes
D) Michaelis-Menten enzymes
E) isozymes

Answer: C
Section: 8.4

10) What term is used to describe the dynamic recognition of the substrate when binding to
an enzyme occurs?

A) allosteric modulation
B) transition state enhancement
C) sequential binding
D) induced fit
E) None of the answers is correct.
Answer: D
Section: 8.3

Fill-in-the-Blank Questions

11. Enzymes accelerate the rate of a chemical reaction by __________________ the

activation energy of the reaction.
Ans: lowering Section: 8.3 and Introduction

12. The difference between the standard-state free energy, ΔGº, and the biochemical
standard-state free energy is that ΔGº′ refers to the standard free-energy change at
________.
Ans: pH 7 Section: 8.2

13. Most known enzymes are proteins; however, some ___________ molecules have been
shown to possess catalytic activity.
Ans: RNA Section: Introduction

14. Organic cofactors are referred to as __________________.

Ans: coenzymes Section: 8.1

15. A reaction can occur spontaneously only if ΔG is __________________.

Ans: negative Section: 8.2

16. When ΔG for a system is zero, the system is at ______________________.

Ans: equilibrium Section: 8.2

17. Compounds that resemble the transition state of a catalyzed reaction and inhibit enzyme
activity are called ____________________________.
Ans: transition-state analogs Section: 8.5

18. Allosteric enzymes can be identified because the plot of initial velocity, V0, versus
substrate concentration, S, is not hyperbolic but __________________ -shaped.
Ans: sigmoidal or “S” Section: 8.4

19. A __________________ inhibitor often has a structure similar to the substrate and often
reversibly binds to the active site of the enzyme but can be displaced by substrate.
Ans: competitive Section: 8.5

20. The straight-line kinetic plot of 1/ V0 versus 1/S is called a ________________________.

 Ans: Lineweaver-Burk plot, or double-reciprocal plot Section: 8.4

Multiple-Choice Questions

21) What is the common strategy by which catalysis occurs?

A) increasing the probability of product formation

B) shifting the reaction equilibrium
C) stabilization of transition state
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: 8.3 and Introduction

22) What conclusion can be drawn concerning an inhibitor if the Vmax is the same in the presence
and absence of the inhibitor?

A) The inhibitor binds to the substrate.

B) The inhibitor can be overcome with sufficiently high concentrations of substrate.
C) The inhibitor reacts with a critical residue of the enzyme.
D) The inhibitor binds to the same active site as the substrate.
E) The KM is smaller in the presence of inhibitor.

Ans: B
Section: 8.5

23) Examples of cofactors include

A) Zn2+, Mg2+, and Ni2+.

B) biotin and thiamine pyrophosphate.
C) pyridoxal phosphate and coenzyme A.
D) biotin and thiamine pyrophosphate and pyridoxal phosphate and coenzyme A
E) All of the answers are correct.

Ans: E
Section: 8.1

24) The formula K'eq = 10G/1.36 indicates the relationship between

A) the free energy and the equilibrium constant.
B) the reaction equilibrium and the isomerization rate.
C) the equilibrium constant and standard free energy.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: 8.2

25) Which of the following is true?

A) Enzymes force reactions to proceed in only one direction.

B) Enzymes alter the equilibrium of the reaction.
C) Enzymes alter the standard free energy of the reaction.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: E
Section: 8.2

26) The Gibbs-free energy of activation is the difference between the

A) substrate and the transition state.
B) substrate and the product.
C) product and the transition state.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: A Section: 8.3

27) The KM is

A) equal to the product concentration at initial reaction conditions.

B) equal to the substrate concentration when the reaction rate is half its maximal value.
C) proportional to the standard free energy.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: B
Section: 8.4
28) Five KM values are given for the binding of substrates to a particular enzyme. Which has the
strongest affinity when k1 is greater than k2?

A) 150 mM
B) 0.15 mM
C) 150 M
D) 1.5 nM
E) 15000 pM

Ans: D
Section: 8.4

29) When substrate concentration is much greater than KM, the rate of catalysis is almost equal to

A) Kd.
B) kcat / KM.
C) Vmax.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: 8.4

30) Which of the following is true under the following conditions: the enzyme concentration is 5
nM, the substrate concentration is 5 mM, and the KM is 5 M?

A) The enzyme is saturated with substrate.

B) Most of the enzyme does not have substrate bound.
C) There is more enzyme than substrate.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: A
Section: 8.4

31) When the kcat / KM ratio is at its upper limit, it is referred to as

A) Circe limits. D) All of the answers are correct.

B) Michaelis rate. E) None of the answers is correct.
C) kinetic perfection.
Ans: C
Section: 8.4

32) Multiple substrate enzyme reactions are divided into two classes which are called

A) sequential displacement and double displacement.

B) double displacement and concerted displacement.
C) sequential displacement and concerted displacement.
D) sequential displacement and double as well as sequential displacement and concerted
displacement are correct.
E) None of the answers is correct.

Ans: A
Section: 8.4

33) What type(s) of inhibition can be reversed?

A) competitive
B) noncompetitive
C) mixed
D) All of the answers are correct.
E) None of the answers is correct.

Ans: D
Section: 8.5

34) In this type of inhibition, the inhibitor can only bind to the ES complex to form an ESI
complex.

A) competitive
B) noncompetitive
C) mixed
D) uncompetitive
E) None of the answers is correct.

Ans: D
Section: 8.5

35) Riboflavin is a water-soluble organic substance that is not synthesized by humans.

Metabolically, it is chemically converted into a substance called flavin adenine dinucleotide,
which is required by succinate dehydrogenase. Which of the following statements is most
correct?

A) Riboflavin is a coenzyme.
B) Flavin adenine dinucleotide is a vitamin.
C) Succinate dehydrogenase is a coenzyme.
D) Flavin adenine dinucleotide is a coenzyme.
Succinate dehydrogenase is a vitamin.

Ans: D
Section: 8.1

Short-Answer Questions

36) In many enzyme assays, the natural substrate and product are not used. Why?
Ans: Many products are difficult to measure accurately. Some are simply difficult to measure,
while others are difficult to discern against the background of other molecules present in the
reaction. Instead, substrates are chosen that the enzyme can still process but that result in
products that can be easily measured. For example, substrates are chosen that result in products
that are colored and can be detected spectrophotometrically.
Section: 8.1

37) Give an example of a reaction catalyzed by a hydrolase.

Ans: Hydrolases catalyze a reaction where a water molecule is added across some linkage that
was originally formed by the removal of water. Some examples are the hydrolysis of an ester, the
hydrolysis of a peptide bond, the hydrolysis of a glycoside bond, etc. A diagram similar to those
used in textbook Section 8.1 are examples.
Section: Appendix

38) There are six basic categories of enzymes. List the categories, and define the type of reaction.
Ans: The categories include oxidoreductases (oxidation–reduction reactions), transferases
(group transfers), hydrolases (hydrolysis reactions), lyases (addition or removal across a double
bond), isomerases (intramolecular group transfer), and ligases (ATP-dependent ligation of
substrates). See textbook Table 8.8 for further details.
Section: Appendix

39) How is the substrate bound to the active site?

Ans: The active site is a small part of the total enzyme structure. It is usually a three-
dimensional cleft or crevice, which is formed by amino acid residues from different regions of
the polypeptide chain. The substrate is bound by multiple noncovalent attractions such as
electrostatic interactions, hydrogen bonds, van der Waals forces, and hydrophobic interactions.
The specificity is dependent on the precise arrangement of the various functional groups in the
binding site.
Section: 8.3

40) You believe a substrate fits rigidly into a cleft like a key into a lock, but your roommate
believes that the structure of the enzyme adapts to the substrate. Who is right?
Ans: You are both partially correct. Like a lock and key, the substrate fits precisely into the
enzyme. However, the site is not a rigid cleft but is flexible. Thus, it is possible for the substrate
to actually modify the shape of the site a bit, a hypothesis known as “induced fit.” See textbook
Figures 8.9 and 8.8 for further detail.
Section: 8.3

41) In an enzymatic reaction in a test tube, the reaction will eventually reach equilibrium. Why
does this not happen in living organisms?
Ans: In a cell, the product may be utilized for a subsequent reaction, thus the reaction may not
reach equilibrium. Furthermore, more substrate may be constantly accumulating or disappearing.
Section: 8.3

42) What is the Michaelis-Menten equation? Define all parameters.

Ans: V0 = Vmax([S]/([S] + KM))

Initial velocity
V0

Maximum velocity
Vmax

Substrate concentration
[S]

Michaelis constant
KM

Section: 8.4

43) What does Vmax indicate?

Ans: The maximum velocity or rate of reaction as catalyzed by a specific amount of enzyme
when it is saturated with substrate.
Section: 8.4
44). What is the upper limit of kcat / KM?
Ans: The diffusion-controlled interaction of the substrate and enzyme determines the upper
limit of the rate. The upper limit is 108–109 s–1M–1. However a few enzymes can overcome this
limit by using Circe forces to attract substrates.
Section: 8.4

45) How do the intermediate steps in multisubstrate enzyme mechanisms differ?

Ans: In a sequential displacement reaction, both substrates bind prior to catalysis and a ternary
complex of all three is formed. In a double displacement (ping-pong), one or more products are
released prior to binding of the second substrate. Thus, a substituted enzyme intermediate is
formed.
Section: 8.4

46). Enzyme populations are studied with the use of ensemble methods. How would the data
differ from a single-enzyme study?
Ans: In the ensemble method study, you would get a single value, which would represent the
average of the heterogeneous assembly of all forms of the enzyme present. Single-enzyme
studies enable biochemists to look into the workings of individual molecules.
Section: 8.6

47) Explain what an abzyme is and give an example.

Ans: Catalytic antibodies are abzymes and are produced using transition-state analogs as
antigens. The example given in the text is an antibody made to a bent porphyrin molecule that
can metallate a porphyrin molecule at a rate 2500-fold faster than the uncatalyzed rate.
Section: 8.5

48) How are the types of inhibition kinetically distinguishable?

Ans: Competitive inhibition can be overcome by the presence of large amounts of substrate.
However, the apparent KM is increased. In noncompetitive inhibition, substrate can bind to the EI
complex, however, the Vmax is decreased. In mixed inhibition, both values may be altered.
Uncompetitive inhibition reduces both Vmax and KM.
Section: 8.5

49) What is an affinity label?

Ans: This is a substrate analog that is structurally similar to the substrate, binds to the active
site, and chemically reacts with a residue in the active site. It is used to study enzyme structure
and mechanism.
Section: 8.5

50) What are transition-state analogs?

Ans: These potent inhibitors mimic the structure of the transition state involved in the catalytic
process. They bind very tightly to the catalytic site and are useful in determining the structure
and catalytic mechanism of the enzyme.
Section: 8.5
Chapter 9 Catalytic Strategies

Multiple-Choice Questions

1) Which of the following is an enzyme that temporarily undergoes covalent catalysis as

part of its mechanism?

A) papain
B) chymotrypsin
C) caspase
D) elastase
E) All of the answers are correct.

Answer: E
Section: 9.1

2) What type of reaction is catalyzed by proteases?

A) oxidation–reduction
B) ligation
C) isomerization
D) hydrolysis
E) group transfer

Answer: D
Section: 9.1

3) What metal ion is required by carbonic anhydrase for activity?

A) Zn2+
B) Mg2+
C) Cu2+
D) Fe2+
E) Ni2+

Answer: A
Section: 9.2

4) What process converts chymotrypsinogen to chymotrypsin?

A) metal ion binding

B) peptide bond cleavage
C) coenzyme association
D) cysteine methylation
E) proline hydroxylation

Answer: B
Section: 9.1

5) What type of assay allows analysis of an enzyme catalyzed reaction in milliseconds?

A) multiple wavelength absorbance spectroscopy

B) fluorescence lifetime
C) stopped-flow
D) NMR
E) None of the answers is correct.

Answer: C
Section: 9.1

6) What modification is made to DNA that protects the host DNA from cleavage by host
restriction endonucleases?

A) acetylation
B) methylation
C) phosphorylation
D) ubiquitination
E) adenylation

Answer: B
Section: 9.3
7) Which of the following techniques allows investigators to test the role of individual
amino acids in the determination of enzyme structure/function relationships even if the
investigated amino acid is not present in the active site?

A) stopped-flow assay
B) use of mechanism based inactivators
C) use of methylating agents
D) site-directed mutagenesis
E) None of the answers is correct.

Answer: D
Section: 9.1

8) What metal ion is frequently found in enzyme active sites that act on phosphate-
containing substrates?

A) Zn2+
B) Mg2+
C) Cu2+
D) Fe2+
E) Ni2+

Answer: B
Section: 9.3

9) What type of symmetry is created by inverted repeats in double-stranded DNA?

A) two-fold rotational
B) three-fold rotational
C) mirror plane
D) line
E) inversion center

Answer: A
Section: 9.3

10) What structures found in proteins are named for the fact that they interact with
phosphoryl groups?
A) P-sheet
B) P-site
C) P-loop
D) P-helix
E) P-turn

Answer: C
Section: 9.4

Fill-in-the-Blank Questions

11. Effective protease inhibitors are often _________________ for one enzyme.
Ans: specific Section: 9.1

12. The catalytic mechanism ofcarbonic anhydrase, in which the substrates are simply
oriented to stabilize the transition state, is called ___________________.
Ans: catalysis by approximation Section: Introduction

13. A-T base pairs, which contain _____ hydrogen bonds, are more easily interrupted than
G-C base pairs with _______ hydrogen bonds.
Ans: two; three Section: 9.3

14. The mechanism of chymotrypsin involves the formation of an unstable

__________________ -shaped intermediate that is stabilized by the oxyanion hole.
Ans: tetrahedral Section: 9.1

15. In trypsin, the specificity pocket contains a/an ______________ residue that binds to the
positive charge of the K or R residue of the substrate.
Ans: aspartyl, aspartic, or D Section: 9.1

16. The reaction center of most carbonic anhydrases is a zinc ion bound to water and
_______________ residues of the enzyme.
Ans: histidine Section: 9.2

17. In chymotrypsin, the tetrahedral intermediate transition state is stabilized by a structural

feature referred to as the “___________________” hole.
Ans: oxyanion Section: 9.2
 18. In proteases such as papain, a ___________________ residue is activated by hydrogen-
bonding to a histidine residue.
Ans: cysteine Section: 9.1

19. Myosins hydrolyze _____________ in a controlled manner and use the free energy of
hydrolysis to promote conformational changes within myosin itself.
Ans: ATP Section: 9.4

20. Kinetic studies on myosins, in the presence and absence of divalent cations, show that
________________ is the true substrate for this enzyme.
Ans: ATP-Mg2+ Section: 9.4

Multiple-Choice Questions

21) Which amino acids in chymotrypsin are found in the active site and are participants in
substrate cleavage?

A) His, Ser, Asp

B) His, Ser
C) Asp, Lys
D) Lys, Arg
E) His, Ser, Arg

Ans: A
Section: 9.1

22) How is specificity determined by chymotrypsin?

A) interaction of the active site amino acids with the substrate

B) binding of the N-terminus amino acid at the active site
C) covalent binding of a His residue to the substrate
D) large conformational change of a P-loop upon binding of substrate
E) binding of the proper amino acid into a deep pocket on the enzyme

Ans: E
Section: 9.1

23) Where does cleavage of the scissile bond by chymotrypsin occur?

A) between a His and Ser amino acid

B) on the N-terminal side of a Phe or Trp residue
C) on the C-terminal side of a Phe or Trp residue
D) at the N-terminal amino acid
E) on the C-terminal side of an Arg or Lys amino acid

Ans: C
Section: 9.1

24) Which of the following is NOT a way in which enzymes stabilize a transition state?

A) causing the temperature of the environment to increase

B) covalent catalysis
C) using binding energy
D) general acid-base catalysis
E) catalysis by approximation

Ans: A
Section: Introduction

25) What do trypsin, subtilisin, and elastase have in common?

A) All contain Asp in the active site.

B) All bind hydrophobic amino acids.
C) All are synthesized in the pancreas.
D) All contain a catalytic triad at the active site.
E) All contain a hydrophilic substrate-binding pocket.

Ans: D
Section: 9.1

26) Convergent evolution is attributed to similarities found between

A) trypsin and elastase.

B) chymotrypsin and elastase.
C) chymotrypsin and subtilisin.
D) chymotrypsin and trypsin.
E) trypsin and kinase.

Ans: C
Section: 9.1
27) If you carried out site-directed mutagenesis of subtilisin, changing serine 221 to isoleucine,
what would you expect?

A) a large change in KM
B) a small change in KM
C) a large change in kcat
D) a large change in KM and a large change in kcat
E) a small change in KM and a large change in kcat

Ans: E
Section: 9.1

28) The metal ion most commonly found at the active site of metalloproteases is

A) zinc.
B) calcium.
C) selenium.
D) magnesium.
E) sodium.

Ans: A
Section: 9.1

29) Carbonic anhydrases are necessary because

A) spontaneous hydration and dehydration of carbon dioxide occur very slowly.

B) spontaneous hydration and dehydration of carbon dioxide are rapid, but not at speeds
necessary for biochemical processes.
C) hydration and dehydration of carbon dioxide are sometimes coupled to other biochemical
processes.
D) spontaneous hydration and dehydration of carbon dioxide occur very slowly, and
hydration and dehydration of carbon dioxide are sometimes coupled to other biochemical
processes
E) spontaneous hydration and dehydration of carbon dioxide are rapid, but not at speeds
necessary for biochemical processes, and hydration and dehydration of carbon dioxide are
sometimes coupled to other biochemical processes.

Ans: E
Section: 9.2

30) Binding of a water molecule to the zinc ion induces

A) a hydronium ion to form.
B) a large conformation change in the binding site.
C) ionization of a His residue, which functions as a strong nucleophile.
D) a lowered pKa for water, which leads to formation of a zinc bound hydroxide ion.
E) an altered KM value.

Ans: D
Section: 9.2

31) Restriction endonucleases cut DNA at specific sites. How many different patterns can be
formed by a four-base sequence combination of any four bases?

A) 64
B) 256
C) 16
D) 1024
E) 4096

Ans: B
Section: 9.3

32) Type II restriction enzymes cut

A) double-stranded DNA, forming a 5' phosphoryl group and a 3' hydroxyl group on each
strand.
B) single-stranded DNA, forming a 5' phosphoryl group and a 3' hydroxyl group on the
strand.
C) double-stranded DNA, forming a 5' phosphoryl group and a 3' hydroxyl group on one
strand.
D) double-stranded DNA, forming a 3' phosphoryl group and a 5' hydroxyl group on each
strand.
E) single-stranded DNA, forming two hydroxyl groups and loss of a phosphate group.

Ans: A
Section: 9.3

33) EcoRV cleaves cognate DNA with a specificity approximately _____ times that of non-
cognate DNA.

A) 10
B) 1000
C) 10,000
D) 1,000,000
E) 100,000,000,000

Ans: D
Section: 9.3

34) Myosins function to

A) transfer the phosphate from NTP to NDP.

B) couple ATP hydrolysis to large conformational changes.
C) couple ATP hydrolysis to glycogen oxidation.
D) phosphorylate NADH.
E) couple ATP hydrolysis to protein synthesis in muscle.

Ans: B
Section: 9.4

35) Metal ion catalysis is facilitated by any of several mechanisms, including

A) stabilizing negative charges on an intermediate.

B) promoting formation of nucleophiles.
C) metals binding directly to substrates.
D) stabilizing negative charges on an intermediate and metals binding directly to substrates.
E) All of the answers are correct.

Ans: E
Section: Introduction

Short-Answer Questions

36) Complete the structure of the catalytic triad of chymotrypsin by drawing the proper structure
of the missing residue side chain in the box provided. Show the proper hydrogen bonding
involved in this triad.

O H O
Asp C O CH2
Ser
CH2
Ans:
His
CH2

O N H O
H N
Asp C O CH2
Ser
CH2

Section: 9.1

37) What is the challenge for a protease to facilitate hydrolysis of a peptide bond?
Ans: The peptide bond contains a carbonyl that is not very reactive; therefore, the catalytic
mechanism must employ a feature that promotes nucleophilic attack of this carbonyl group by a
strong nucleophile so the peptide bond can be cleaved.
Section: 9.1

38) How can covalent modification be used to determine the mechanism of action of an enzyme?
Ans: If a particular amino acid side chain is suspected of participating in a catalytic
mechanism, covalent modification of the residue may alter it sufficiently that the enzyme activity
is altered or inhibited. However, this method is usually confirmed by other techniques, such as
site-directed mutagenesis, to rule out other possible reasons for the loss of activity, such as global
conformational change as a result of the modification.
Section: 9.1

39) Why are substrate analogs often used to monitor enzyme activity?
Ans: Enzyme assays must be designed so that formation of a product is rapidly and easily
monitored. Substrates that form a colored product are easy to observe in a quantitative manner
using spectrophotometers.
Section: 9.1

40) What caused a “burst” of activity followed by a steady-state reaction when chymotrypsin
was studied by stop-flow techniques?
Ans: Chymotrypsin cleaves peptide bonds in a two-step reaction, in which the first step,
formation of the acyl enzyme intermediate, is faster than the second step, hydrolysis.
Section: 9.1

41) What supports the theory that a catalytic triad strategy is a result of convergent evolution?
Ans: A number of different enzymes, including the peptidase family, some esterases, and
others, have similar mechanisms of actions. While the strategy is similar, the actual participating
amino acids differ, suggesting a mechanism commonly employed as a result of convergent
evolution.
Section: 9.1

42) What is the common strategy for cysteine, metallo-, and aspartyl proteases?
Ans: All employ a mechanism whereby a nucleophile is generated that attacks the carbonyl of
the peptide bond.
Section: 9.1

43) What is the common nucleophile found in cysteine, metallo-, and aspartyl proteases?
Ans: The common nucleophile is water.
Section: 9.1

44) Designing drugs to inhibit enzymes is a large part of pharmaceutical research. What are
some of the enzymatic features that would be important?
Ans: The enzyme could be inhibited by interaction of a potential drug at the active site or at a
site that alters conformation or regulation of the enzyme. The structure of natural substrates and
activators, and their binding sites, would be useful features to study for a new drug design. The
binding affinity and specificity would be important, and standard enzyme assays would be used
to determine the effect of the inhibitors on kcat, KM, and Vmax.
Section: 9.1

45) How is the bicarbonate formed when carbonic anhydrase is present?

Ans: The zinc promotes formation of a hydroxide ion, which attacks the carbon dioxide.
Section: 9.2

46) What features of carbonic anhydrase allow the rapid hydration of carbon dioxide?
Ans: Bringing the two reactants (carbon dioxide and water) into proximity facilitates the rapid
reaction rate, and the presence of a buffer system aids in proton transfer and release.
Section: 9.2

47) What mechanism is responsible for restriction endonuclease cleavage of DNA?

Ans: An activated water molecule directly attacks the phosphorous atom in a single
displacement reaction.
Section: 9.3

48) The sequence 6 bp restriction cleavage site for EcoRV is GATXXX. What is the complete
sequence of the double-stranded restriction site?
Ans: GATATC
CTATAG
Section: 9.3
49) What is significant about the slow rate for myosin’s hydrolysis of ATP?
Ans: The persistence of a conformation of myosin with ATP hydrolyzed but still bound is
critical for coupling conformational changes that take place in the course of the reaction to other
processes.
Section: 9.4

50) Describe the secondary and tertiary structures in domains that form P-loops and bind
phosphoryl groups.
Ans: This domain structure consists of a central β sheet, surrounded on both sides by α helices.
Characteristically, there is a loop between the first β strand and the first helix that contains
several glycine residues.
Section: 9.4
Chapter 10 Regulatory Strategies

Multiple-Choice Questions

1) What regulatory mechanism relies on inhibition of the first step of the pathway by the
final product of the pathway?

A) competitive inhibition
B) uncompetitive inhibition
C) allosteric inhibition
D) feed-forward inhibition
E) feedback inhibition

Answer: E
Section: Introduction

2) What term describes multiple forms of homologous enzymes found within an organism?

A) zymogens
B) holoenzymes
C) isoenzymes
D) consensus enzymes
E) None of the answers is correct.

Answer: C
Section: Introduction

3) What term describes enzymes that are activated by proteolytic cleavage?

A) phosphatases
B) isozymes
C) kinases
D) zymogens
E) apoenzymes

Answer: D
Section: Introduction
4) The less active conformational form of an allosteric enzyme is called the _____.

A) T-state
B) M-state
C) R-state
D) I-state
E) L-state

Answer: A
Section: 10.1

5) What shape is seen in the kinetic plot of an enzyme that exhibits cooperative binding?

A) sigmoidal
B) hyperbolic
C) parabolic
D) linear
E) None of the answers is correct.

Answer: A
Section: 10.1

6) Which of the following is the most crucial pathway for blood clotting?

A) intrinsic pathway
B) extrinsic pathway
C) coagulation pathway
D) fibrinogen activation pathway
E) prothrombin activation pathway

Answer: B
Section: 10.4

7) Which type of enzymes specifically catalyzes protein phosphorylation?

A) protein ATPase
B) protein transferases
C) protein phosphatases
D) protein kinases
E) None of the answers is correct.

Answer: D
Section: 10.3

8) Removal of protein phosphates is catalyzed by protein _____.

A) phosphate hydrolase
B) phosphatase
C) kinase
D) dephosphorylase
E) None of the answers is correct.

Answer: B
Section: 10.3

9) What molecule is required for the proper production of prothrombin?

A) factor Xa
B) factor Va
C) tissue factor
D) fibrin
E) vitamin K

Answer: E
Section: 10.4

10) Which modified amino acid is found in prothrombin that allows for Ca2+ binding?

A) acetyl lysine
B) phosphoserine
C) -carboxyglutamate
D) hydroxyproline
E) None of the answers is correct.
Answer: C
Section: 10.4

Fill-in-the-Blank Questions

11. _______________ are multiple forms of homologous enzymes within the same
organism that catalyze the same reaction but with different kinetic properties.
Ans: Isozymes or Isoenzymes Section: Introduction

12. Aspartyl transcarbamylase catalyzes the first step in the synthesis of ______________.
Ans: pyrimidines Section: 10.1

13. p-Hydroxymercuribenzoate displaces Zn2+ from binding to crucial ______________

residues in ATCase.
Ans: cysteine Section: 10.1

14. The effects of substrates on allosteric enzymes are referred to as ___________________

effects.
Ans: homotropic Section: 10.1

15. Blood serum analysis of ____________________________ isozymes is used in the

diagnosis of a myocardial infarction.
Ans: lactate dehydrogenase or LDH Section: 10.2

16. The ____________ pathway is activated by exposure of anionic surfaces on ruptured

endothelial cells.
Ans: intrinsic Section: 10.4

17. Histones are acetylated at specific ________________ residues.

Ans: lysine Section: 10.3

18. Protein kinases add phosphoryl groups to serine, threonine, and _________________
residues in target proteins.
Ans: tyrosine Section: 10.3

19. Protein kinase A is activated by the binding of ________________ to specific sites on

the regulatory subunit.
Ans: cAMP Section: 10.3
 20. A ______________ is an inactive precursor of an enzyme that is activated by a
proteolytic cleavage.
Ans: zymogen or proenzyme Section: 10.4

Multiple-Choice Questions

21) What is (are) the most common strategy(ies) for enzymatic regulation?

A) multiple enzyme forms

B) allosteric control
C) reversible covalent modification
D) proteolytic activation
E) All of the answers are correct.

Ans: E
Section: Introduction

22) Allosteric proteins

A) usually display hyperbolic Michaelis-Menten kinetics.

B) often display cooperativity.
C) always consist of several identical subunits.
D) usually display hyperbolic Michaelis-Menten kinetics and often display cooperativity.
E) All of the answers are correct.

Ans: B
Section: Introduction and 10.1

23) Many allosteric enzymes have two types of subunits, termed

A) catalytic and regulatory.

B) regulatory and allosteric.
C) allosteric and regulatory.
D) R-state and T-state.
E) None of the answers is correct.

Ans: A
Section: 10.1
24) Changes in ATCase conformation were detected by crystallizing the enzyme in the presence
of PALA (N-(phosphonacetyl)-L-aspartate). What is PALA?

A) a radioactive tag that binds to the subunits

B) a substrate analog that resembles the transition state
C) a fluorescent allosteric inhibitor analog
D) All of the answers are correct.
E) None of the answers is correct.

Ans: B
Section: 10.1

25) The relaxed form of an allosteric enzyme has _________ affinity for the substrates than the
tense form.

A) higher
B) equal
C) lower
D) no
E) None of the answers is correct.

Ans: A
Section: 10.1

26) The regulatory effects of substrates on allosteric enzymes are referred to as

_______________ effects.

A) homotropic
B) heterotropic
C) allotropic
D) All of the answers are correct.
E) None of the answers is correct.

Ans: A
Section: 10.1

27) Examples of covalent modification include

A) phosphorylation and dephosphorylation.

B) acetylation.
C) ubiquitination.
D) All of the answers are correct.
E) phosphorylation, dephosphorylation, and acetylation.

Ans: D
Section: 10.1

28) Multifunctional protein kinases

A) carry out phosphorylation as well as sulfation reactions.

B) can modify several different targets.
C) conserve energy in the form of ATP from the degradation of proteins.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: B
Section: 10.3

29) Multifunctional kinases phosphorylate proteins by recognizing related sequences called

A) cAMP binding sequences.

B) calmodulin binding sequences.
C) pseudosubstrate sequences.
D) consensus sequences.
E) palindromes.

Ans: D
Section: 10.3

30) Which of the following is an example of a zymogen?

A) pepsinogen
B) procarboxypeptidase
C) T-form of ACTase
D) All of the answers are correct.
E) pepsinogen and procarboxypeptidase

Ans: E
Section: Table 10.3

31) How is chymotrypsinogen activated?

A) cleavage between an Arg and Ile by chymotrypsin
B) cAMP binding, followed by cleavage by elastase
C) cleavage between an Arg and Ile by trypsin
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: 10.4

32) One type of hemophilia is due to

A) vitamin K deficiency.
B) loss of the gene for prothrombin.
C) loss of the gene for antihemophilic factor.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: 10.4

33) How is trypsin activity turned off?

A) by dephosphorylation
B) by binding an inhibitor protein
C) by a second cleavage
D) All of the answers are correct.
E) by dephosphorylation and binding an inhibitor protein

Ans: B
Section: 10.4

34) Blood clotting cascades are controlled mostly by

A) zymogen activation.
B) phosphorylation.
C) allosteric activation.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: A
Section: 10.4
35) A regulatory mechanism that is NOT readily reversible is

A) phosphorylation.
B) allosteric control.
C) proteolytic cleavage.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: Introduction

Short-Answer Questions

36) What is the function of aspartate transcarbamoylase?

Ans: The enzyme catalyzes the first step in the synthesis of pyrimidines. It condenses
carbamoyl phosphate and aspartate to form N-carbamoylaspartate and inorganic phosphate.
Section: 10.1

37) Give several examples of enzymes and proteins that are activated by proteolytic activation.
Ans: Examples include digestive enzymes (trypsin), hormones (insulin), clotting enzymes
(fibrinogen), developmental process proteins (collagen), and apoptosis proteins (caspases).
Section: Introduction and 10.4

38) Why might it have been surprising to find that CTP inhibits ATCase?
Ans: The substrates for ATCase are carbamoyl phosphate and aspartate. These molecules do
not resemble CTP. Thus, it was clear that the CTP must not bind to the active site but to a distinct
regulatory site.
Section: 10.1

39) Do allosteric enzymes follow traditional Michaelis-Menten kinetics? Draw a graph of rate
relative to substrate concentration for ATCase and compare it to a Michaelis-Menten enzyme.
Ans: No, ATCase displays different kinetics. A plot of rate versus substrate concentration is a
sigmoidal curve, as opposed to the simple hyperbolic curve obtained by enzymes displaying
Michaelis-Menten kinetics.
Section: 10.1 and Figure 10.14

40) How does the sequential model differ from the concerted model for allosteric enzymes?
Ans: The concerted model does not allow for anything other than an “all-or-none” complete
tense- or relaxed-form protein. In contrast, the sequential model allows for a mixed type of
protein, containing some tense and some relaxed subunits. The form is in response to the ligand
binding by a particular subunit.
Section: 10.1

41) What protein is administered after heart attacks to increase survival odds, and what is the
biochemistry involved?
Ans: Tissue-type plasminogen activator, or TPA. TPA leads to the dissolution of blood clots so
that blood flow through the blocked coronary artery can be restored. TPA activates plasminogen
that is bound to the fibrin clot to active plasmin, which then hydrolyzes the fibrin of the clot.
Section: 10.4

42) Why are certain forms of lactate dehydrogenase used as heart attack indicators?
Ans: LDH is a tetramer, made of M and H isozyme subunits. The M tetramer functions in an
anaerobic environment and is primarily found in skeletal tissue, whereas the H tetramer, found
primarily in the heart, functions optimally in an aerobic environment. An excess of the H type in
serum indicates that a heart attack occurred.
Section: 10.2

43) Why is covalent modification advantageous when compared to proteolytic activation?

Ans: Covalent modification is usually a reversible process.
Section: 10.3

44) How can cleavage of a single peptide bond activate a zymogen?

Ans: The switching on of enzymatic activity in a protein can be accomplished by discrete,
highly localized conformation changes that are triggered by the hydrolysis of a single peptide
bond.
Section: 10.3

45) Describe how the PKA kinase cascade is activated.

Ans: The process is often initiated by hormones that bind to membrane receptors. This process
activates adenylate cylase, which causes the formation of cAMP, an intracellular messenger. The
cAMP activates a key protein kinase. In eukaryotic cells this is an allosteric enzyme, protein
kinase A, which then phosphorylates various target proteins.
Section: 10.3

46) How does cigarette smoking relate to elastase function?

Ans: 1-antitrypsin is a neutrophil protein that inhibits elastase. Some individuals with a
genetic disease causing deficiency of functional 1-antitrypsin have scarred lungs due to
overactive elastase. This generally occurs in individuals who are homozygous for a
polymorphism. H however, one side effect of smoking is oxidation of a Met in the 1-antitrypsin
in a heterozygous individual, and it no longer functions efficiently as an inhibitor. Thus, both a
genetic disorder and smoking can lead to emphysema.
Section: 10.3

47) How is the clotting cascade initiated?

Ans: Both intrinsic (damaged surface) and extrinsic (trauma) pathways can induce the cascade.
The initial steps differ but lead to a final common path to form the fibrin clot.
Section: 10.4

48) What is the final step in the clotting pathway?

Ans: In the final step, fibrinogen, which contains six chains of three subunit types, is altered.
Thrombin cleaves four of the chains, resulting in the formation of fibrin monomers. These
monomers spontaneously assemble into the fibrin array. The clot is stabilized by cross-links
between the amino acids catalyzed by transglutaminase.
Section: 10.4

49) What is the dual action of thrombin?

Ans: Thrombin catalyzes the hydrolysis of fibrinogen to form active fibrin. But it also has a
role in shutting down the cascade by activating protein C, a protease that digests other clotting
enzymes Va and VIIIa.
Section: 10.4

50) Individuals in a royal family suffered from hemophilia and often died early from bleeding.
What is the cause of this disease? How is it treated?
Ans: The disease in the royal family was caused by faulty factor VIII of the intrinsic pathway.
It is treated by the addition of supplemental protein, originally isolated from serum, but now a
recombinant product.
Section: 10.4 and Figure 10.36
 Chapter 11 Carbohydrates

Multiple-Choice Questions

1) Which of the following terms describes a class of compounds with the molecular formula
(CH2O)n?

A) proteoglycans
B) glycogen
C) mucoproteins
D) polysaccharides
E) monosaccharides

Answer: E
Section: 11.1

2) What term describes stereoisomers that are mirror images of each other?

A) anomers
B) epimers
C) enantiomers
D) diastereomers
E) meso compound

Answer: C
Section 11.1

3) Two monosaccharides that differ in stereochemistry at only a single asymmetric carbon are
called _____.

A) aldoses
B) epimers
C) anomers
D) pentoses
E) enantiomers

Answer: B
Section: 11.1

4) Which of the following is among the most abundant organic molecules in the biosphere?

A) glycogen
B) amylose
C) amylopectin
D) cellulose

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 2

E) chitin

Answer: D
Section: 11.2

5) Fehling’s solution is used to differentiate between reducing and nonreducing sugars. Which
type of ion in Fehling’s solution allows for this differentiation?

A) cupric
B) sodium
C) iodide
D) hydroxide
E) bicarbonate

Answer: A
Section: 11.1

6) Which of the following is the storage form of glucose in animals?

A) glycogen
B) amylose
C) amylopectin
D) cellulose
E) chitin

Answer: A
Section: 11.2

7) ______is the class of glycoproteins with predominantly N-acetylgalactosamine moieties.

A) Glycosaminoglycans
B) Mucoproteins
C) Starch
D) Lectins
E) Proteoglycans

Answer: B
Section: 11.3

8) What type of enzyme synthesizes oligosaccharides?

A) amylase
B) sucrase
C) glycosyltransferase
D) -galactosidase
E) protein kinase

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 3

Answer: C
Section: 11.3

9) What molecule are most sugars attached to prior to their transfer to proteins?

A) GDP
B) GMP
C) AMP
D) UMP
E) UDP

Answer: E
Section: 11.3

10 Which of the following are proteins that bind to specific carbohydrate structures in order
) to facilitate recognition between proteins and cells?

A) mucoproteins
B) glycosaminoglycans
C) glycoproteins
D) lectins
E) proteoglycans

Answer: D
Section: 11.4

Fill-in-the-Blank Questions
11) A _______________ is a stereoisomer that is not a mirror image.
Ans: diastereoisomer Section: 11.1

12) A _______________ is a five-membered ring formed from a monosaccharide.

Ans: furanose Section: 11.1

13) When an open-chain aldose cyclizes into a ring, it forms a _______________.

Ans: hemiacetal Section: 11.1

14) Plant starch is composed of amylose, a linear polymer of glucose, and a branched polymer of
glucose referred to as _______________.
Ans: amylopectin Section: 11.2

15) Maltose is composed of two molecules of glucose linked together by a(n) ____________
glycosidic bond.
Ans: α-1,4 Section: 11.2

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 4

16) _______________ is a disaccharide composed of galactose and glucose joined by a β-1,4

glycosidic bond.
Ans: Lactose Section: 11.2

17) In N-linked glycoproteins, the carbohydrate portion is attached to a(n)_____________ residue in

the protein.
Ans: asparagine Section: 11.3

18) A given protein with several potential glycosylation sites can have many different glycosylated
structures called ________________.
Ans: glycoforms Section: 11.3

19) The influenza virus recognizes _______________ (a carbohydrate) residues of glycoproteins

present on cell surface.
Ans: sialic acid Section: 11.4

20) In C-type lectins, a _______________ acts as a bridge between the carbohydrate and the
protein.
Ans: calcium ion Section: 11.4

Multiple-Choice Questions
21) Common carbohydrates found in nature are
A) aldehydes with two or more hydroxyl groups.
B) ketones with two or more hydroxyl groups.
C) amines with two or more hydroxyl groups.
D) aldehydes with two or more hydroxyl groups and ketones with two or more hydroxyl
groups.
E) All of the answers are correct.
Ans: D Section: 11.1

22) The simplest carbohydrates are the 3-carbon molecules:

A) D- and L-glyceraldehyde.
B) dihydroxyacetone and D- and L-glyceraldehyde.
C) dihydroxyacetone and glycerate.
D) dihydroxyacetone and glycerol
E) None of the answers is correct.
Ans: B Section: 11.1

23) An aldehyde and alcohol can react to form a

A) hemialdol. D) All of the answers are correct.
B) hemiketal. E) None of the answers is correct.
C) hemiacetal.
Ans: C Section: 11.1

24) Fructose can cyclize to (a)

A) pyranose ring.
B) furanose ring.

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 5

C) both pyranose and furanose ring forms.

D) All of the answers are correct.
E) None of the answers is correct.
Ans: C Section: 11.1

25) The nutritional storage form(s) of glucose in plants is/are

A) glycogen. B) amylose. C) amylopectin. D) cellulose. E) amylose and amylopectin.
Ans: E Section: 11.2

26) The enzyme that digests amylopectin is

A) -amylase. D) invertase.
B) amylopectinase. E) None of the answers is correct.
C) cellulase.
Ans: A Section: 11.2

27) Sugars are commonly linked to which amino acid residues in glycoproteins?
A) tyrosine and asparagine D) serine and glutamine
B) serine, threonine, and asparagine E) threonine and glutamine
C) serine, tyrosine, and asparagine
Ans: B Section: 11.3

28) Glycoproteins are normally

A) found on membranes. D) All of the answers are correct.
B) secreted as extracellular proteins. E) found on membranes and secreted as
extracellular proteins.
C) found inside organelles.
Ans: E Section: 11.3

29) At what location(s) within a cell is/are proteins glycosylated?

A) ribosome D) lysosome
B) endoplasmic reticulum E) endoplasmic reticulum and Golgi
complex
C) Golgi complex
Ans: E Section: 11.3

30) Which of the following is the anomer of β-D-glucopyranose?

A) CH2OH CH2OH CH2OH
C) E)
OH O OH O O OH
OH OH OH OH
OH OH OH
OH OH
B) CH2OH
D)
O CH2OH OH
O
OH OH
OH OH
OH OH
Ans: C Section: 11.1

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 6

31) Glycoform refers to

A) a single protein type that can have forms that differ only in their glycosylation.
B) glycoproteins from the same gene family.
C) a common core of sugars that can be found on many different proteins.
D) All of the answers are correct.
E) None of the answers is correct.
Ans: A Section: 11.3

32) Selectins are proteins that

A) selectively bind proteins destined for lysozomes.
B) aid in selection of proteins bound for the Golgi complex.
C) bind immune-system cells as part of the inflammatory response.
D) All of the answers are correct.
E) None of the answers is correct.
Ans: C Section: 11.4

33) What are lectins?

A) proteins that bind the carbohydrates on glycoproteins and other macromolecules
B) proteins that promote cellcell interaction
C) proteins found in animals, plants, and microorganisms
D) All of the answers are correct.
E) None of the answers is correct.
Ans: D Section: 11.4.

34) Which of the following explains how some viruses gain entry into specific cells?
A) by attaching to ion channels
B) by cleaving the glycosidic bonds of cell surface glycoproteins and altering protein shapes
C) by binding to glycoproteins on the cell surface that are unique to specific cells
D) All of the answers are correct.
E) None of the answers is correct.
Ans: C Section: 11.4

35) Inhibitors against which viral enzyme have potential as anti-influenza agents?
A) Calnexin D) All of the answers are correct.
B) Neuraminidase E) None of the answers is correct.
C) Selectin
Ans: B Section: 11.4

Short-Answer Questions
36) List some of the reasons why carbohydrates are considered important molecules.
Ans: Carbohydrates serve several important functions as fuels, metabolic intermediates, and
energy stores. They are the basis of most of the organic matter on our planet.
Carbohydrates serve as the structural framework or building blocks for DNA, RNA, and
polysaccharides. They are also linked to other molecules, such as proteins and lipids, and
play important roles in signaling and structure.

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 7

Section: Introduction

37) Draw the Fischer projection structures of all of the trioses.

Ans:

dihydroxyacetone D-glyceraldehyde L-glyceraldehyde

Structures shown in Figure 11.1.
Section: 11.1 and Figure 11.1

38) What is the difference between an enantiomer and a diastereoisomer? Give examples.
Ans: An enantiomer is a stereoisomer that is a perfect (nonsuperimposable or nonidentical)
mirror image. A chiral molecule has one perfect mirror image. However, for larger
carbohydrates that have the same chemical formula and have multiple chiral centers,
variations in asymmetric carbon structures mean that additional stereoisomers exist. The
stereoisomers that are not mirror images of each other are called diastereoisomers.
D-glucose and D-mannose are diastereoisomers, and D-glyceraldehyde and
L-glyceraldehyde are enantiomers.
Section: 11.1

39) How is the D or L configuration determined?

Ans: The D or L configuration is determined by the asymmetric carbon farthest from the ketone
or aldehyde group and is related to the glyceraldehyde D and L structures.
Section: 11.1

40) Draw the Haworth projections of the two pyranose forms of D-glucose.
Ans: CH2OH CH2OH
O O OH
OH OH
OH OH OH
OH OH
α-D-glucopyranose β-D-glucopyranose
As shown in Figures 11.1 and 11.3 of the text.
Section: 11.1

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 8

41) Draw the structure of lactose. Identify the monosaccharides involved, and identify the type of
linkage in lactose.
Ans: D-glucose ( anomer)
CH2OH
D-galactose O
CH2OH OH
OH O O OH
OH OH

OH 1-4 glycosidic linkage

Section: 11.2

42) Compare the structures of amylopectin and amylose.

Ans: Both are homopolymers of glucose. Amylose consists of unbranched -1,4 linkages of
glucose. Amylopectin is a branched structure and contains both -1,4 linkages and -1,6
linkages, with the -1,6 branches occurring about once every 30 glucose residues.
Section: 11.2

43) What are the chemical and structural differences between cellulose and glycogen?
Ans: Both are glucose homopolymers. Glycogen is a branched polymer and contains -1,4
linkages with α-1,6 branchpoints about every 10 residues. Cellulose is a linear polymer
that contains -1,4 linkages. Because of the  linkages, cellulose can form very long
straight chains, which can form interchain hydrogen bonds to form fibrils.
Section: 11.2

44) Describe some of the functions of glycosaminoglycans and proteoglycans.

Ans: They function as lubricants, anticoagulants, and structural components; are important in
pathways stimulating cell proliferation; and aid in mediating cell adhesion to extracellular
matrices.
Section: 11.2

45) How does a genetic mutation account for some of the different human blood types?
Ans: Blood type is determined by specific glycosyltransferases that add the end sugar to the
glycoproteins found on red blood cells. Three different types of glycosyltransferase genes
can be inherited, and each individual receives one from each parent. Two different forms
result in the A and B blood types. A mutation in a third type results in a truncated product
that is not active. Homozygous individuals with this third type will be type O.
Section: 11.3

46) What is the advantage of having different blood types within a species?
Ans: Variations are protective because differences may be critical to protection against disease
and infection. A microorganism that gains advantage over a host by mimicking and/or
using specific antigens will not survive in host members that have differing antigens.
Section: 11.3

47) Describe the mechanism by which N-linked sugars are synthesized and attached to proteins.
Ans: The units are assembled in the ER attached to a dolichol phosphate scaffold. Two
N-acetylglucosamine residues and five mannose residues are added to form a common

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
 Chapter 11 Carbohydrates 9

precursor, which is flipped into the ER lumen. Then, specific enzymes add dolichol-
phosphatelinked sugars, forming a 14-residue core. This is transferred to an asparagine
residue on a protein, and the sugar core is processed by removal of three glucose
molecules. The addition and removal of other sugars in the Golgi complex further modify
the carbohydrate.
Section: 11.3 and Figure 11.24

48) What is the role of L-selectin when produced by an embryo?

Ans: L-Selectin is produced by embryos when they are ready to attach to the endometrium of
the mother’s uterus. For a short period of time, the endometrial cells present an
oligosaccharide on the cell surface. When the embryo attaches through this lectin, the
attachment activates signal pathways in the endometrium to make implantation of the
embryo possible.
Section: 11.4

49) What is the role of mannose 6-phosphate? What disease is caused by lack of this terminal sugar
on glycoproteins?
Ans: It acts as the marker that directs many lysosomal enzymes to their proper site. Without the
modified mannose residue, the proteins are misdirected. For example, in I-cell disease,
several enzymes are directed to blood and urine instead of the lysosomes. As a result,
hydrolases required for glycosaminglycan and glycolipid degradation are missing, leading
to deformity and retardation.
Section: 11.3

50) Why is it more difficult to determine the structure of the oligosaccharides, when compared to
amino acid sequences?
Ans: Amino acids are linked through peptide bonds and the side chains vary in size, charge,
and chemical properties. In contrast, sugars can be branched and can have  or 
linkages, which makes determining the attachment difficult. Furthermore, many sugars
have the same or similar chemical formula(s), and similar chemical properties, making
specific identification and linkage difficult.
Section: 11.3

This study source was downloaded by 100000830124955 from CourseHero.com on 12-21-2021 09:31:09 GMT -06:00

https://www.coursehero.com/file/19574192/berg-8e-testbank-chapter111/
Powered by TCPDF (www.tcpdf.org)
Chapter 12 Lipids and Cell Membranes

Multiple-Choice Questions

1) What important property is conferred on membranes by transport systems?

A) asymmetry
B) selective permeability
C) bilayer
D) amphipathic nature
E) None of the answers is correct.

Answer: B
Section: Introduction

2) What is the number of carbons found in the most commonly observed fatty acids?

A) 12 or 14
B) 14 or 16
C) 16 or 18
D) 18 or 20
E) 20 or 22

Answer: C
Section: 12.1

3) In addition to phospholipids and glycolipids, which of the following is a major type of

membrane lipid?

A) cholesterol
B) vitamin E
C) triacylglycerol
D) free fatty acids
E) None of the answers is correct.

Answer: A
Section: 12.2
4) What term describes molecules that have both hydrophilic and hydrophobic moieties?

A) amphoteric
B) amphiprotic
C) amphibian
D) amphipathic
E) None of the answers is correct.

Answer: D
Section: 12.2

5) What substance inhibits prostaglandin H2 synthase-1 by blocking the channel through

which the substrate, arachidonate, travels?

A) acetaminophen
B) Celebrex
C) ibuprofen
D) Vioxx
E) acetylsalicylic acid

Answer: E
Section: 12.4

6) What protein polymerizes into a lattice network around a budding membrane?

A) porin
B) clathrin
C) epsin
D) G protein
E) glycophorin

Answer: B
Section: 12.6

7) What property is used to determine the probability that a segment of a protein will be
found embedded in a membrane?
A) hydropathy
B) polarity
C) acidity
D) entropy
E) solvation

Answer: A
Section: 12.4

8) What is the most common process by which lipids and proteins move in the membrane
bilayer?

A) kinesin-mediated movement
B) flip-flopping
C) translocation
D) lateral diffusion
E) asymmetric longitudinal flipping

Answer: D
Section: 12.5

9) What membrane components contain carbohydrates?

A) lipid-linked proteins
B) cholesterol
C) integral membrane proteins in contact with the cytoplasm
D) phosphatidylserine
E) glycolipids

Answer: E
Section: 12.2

10) What complex is observed between cholesterol and membrane phospholipids?

A) salt bridge
B) clathrate
C) lipid raft
D) phospholipid domain
E) None of the answers is correct.

Answer: C
Section: 12.5

Fill-in-the-Blank Questions

11. ________________ is a membrane lipid composed of sphingosine, fatty acid, and a

simple sugar like glucose or galactose.
Ans: Cerebroside Section: 12.2

12. __________________ contain a double bond three carbons from the distal end of the
fatty acid.
Ans: ω-3 Fatty acids Section: 12.1

13. In phosphoglycerides, the fatty acids are linked to the glycerol backbone by
______________ linkages.
Ans: ester Section: 12.2

14. Ionized fatty acids readily form ______________ in aqueous solutions.

Ans: micelles Section: 12.2

15. ___________________ are aqueous compartments enclosed by a lipid bilayer which can
be created in a laboratory.
Ans: Lipid vesicles, or liposomes, Section: 12.3

16. ___________________ membrane proteins are bound to membranes primarily by

electrostatic and hydrogen bond interactions with the head groups of lipids.
Ans: Peripheral Section: 12.4

17. Some proteins are anchored to the membrane by being covalently attached to a
_______________ group by a thioester linkage to a specific (non-C-terminal) cysteine
residue.
Ans: palmitoyl Section: 12.4

18. The rate of diffusion is such that a phospholipid molecule can travel from one end of a
bacterium to the other in _______________ of time.
Ans: 1 second Section: 12.5
 19. The temperature at which a phospholipid membrane transitions from a rigid to a fluid
state is referred to as _______________.
Ans: Tm, or melting temperature Section: 12.5

20. In animals, ________________ is the key regulator of membrane fluidity.

Ans: cholesterol Section: 12.5

Multiple-Choice Questions

21) Membranes are primarily comprised of

A) lipids.
B) proteins.
C) carbohydrates.
D) All of the answers are correct.
E) A and B.

Ans: E
Section: Introduction

22) Which of the following is true?

A) Membranes are lipid bilayers.

B) Membrane lipids have both hydrophobic and hydrophilic properties.
C) Many membranes are electrically polarized.
D) All of the answers are correct.
E) A and B.

Ans: D
Section: Introduction

23) How many molecules thick are membranes?

A) one
B) two
C) infinite
D) varying thickness, depending on structure
E) None of the answers is correct.
Ans: B
Section: Introduction

24) Which of the following membranes would be the most fluid?

A) a bilayer made of lipids with polyunsaturated 18 carbon-fatty acids

B) a bilayer made of lipids with saturated 18 carbon-fatty acids
C) a bilayer made of lipids with saturated 16 carbon-fatty acids
D) a bilayer made of lipids with polyunsaturated 16 carbon-fatty acids
E) All of the above are equivalent in fluidity.

Ans: D
Section: 12.1

25) Which of the following statements is consistent with the structure of biological membranes?

A) All membrane proteins are integral and associate with the hydrophobic region of the
membrane.
B) Both proteins and lipids readily undergo transverse (“flip-flop”) diffusion from the inside
to the outside of the membrane.
C) Membranes are symmetric.
D) The membrane lipids self-assemble to form the lipid bilayer.
E) A biological membrane consists of proteins sandwiched between two layers of lipids,
which are referred to as a lipid bilayer.

Ans: D
Section: 12.3

26) Which of the following is NOT correct concerning the structure given?

O
H H O CH2 O C(CH2)14CH3
CH3(CH2)7C C(CH2)7C O CH O
+
CH2 OPOCH2CH2N(CH3)3
O-

A) It is a component of biological membranes.

B) It is amphipathic.
C) It is a sphingolipid.
D) It is a phosphoglyceride.
E) It is phosphatidyl choline.
Ans: C
Section: 12.2

27) How do the membranes of archaea differ from bacteria and eukaryotes?

A) The lipids do not contain a carboxylic acid ester, but instead have an ether link to the
glycerol.
B) The alkyl chains are branched.
C) The stereochemistry of the central carbon of glycerol is inverted.
D) A and C are correct.
E) All the answers are correct.

Ans: E
Section: 12.2

28) Carbohydrate residues attached to the membrane lipids are almost always

A) positioned on the intracellular side of the membrane.

B) positioned on the inside center of the bilayer.
C) positioned on the extracellular side of the membrane.
D) positioned equally on both sides of the membrane.
E) also covalently attached to membrane proteins.

Ans: C
Section: 12.2

29) What force(s) stabilize(s) the lipid bilayers?

A) van der Waals interactions

B) electrostatic and hydrogen bonding between the polar heads and surrounding water
C) covalent bonds between the lipids and membrane proteins
D) van der Waals interactions and electrostatic and hydrogen bonding between the polar
heads and surrounding water

E) electrostatic and hydrogen bonding between the polar heads and surrounding water
and covalent bonds between the lipids and membrane proteins

Ans: D
Section: 12.3
30) The degree of membrane fluidity in bacteria depends mainly on the percentage of

A) lipids that contain sphingosine.

B) glycolipids.
C) free fatty acids.
D) unsaturated fatty acids.
E) None of the answers is correct.

Ans: D
Section: 12.5

31) Which of the following membrane-bound organelles is thought to have evolved from bacteria
by endosymbosis?

A) peroxisomes
B) mitochondria
C) cell walls
D) nuclei
E) endoplasmic reticulum

Ans: B
Section: 12.6

32) The most common motif found in membrane spanning proteins is

A)  helices of nonpolar amino acids that pass through the membrane.

B)  helices of charged amino acids that form channels via extensive hydrogen bonding.
C) a triple helix of  helices.
D) a helix-turn-helix arrangement of the peptide strands.
E) None of the answers is correct.

Ans: A
Section: 12.4

33) Hydrophobic molecules can be covalently attached to proteins to increase membrane

association. Type(s) of group(s) include

A) palmitoyl groups attached via Cys residues.

B) glycolipid structures attached to the carboxy terminus.
C) farnesyl groups attached via Cys residues.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: D
Section: 12.4

34) The low incidence of protein or lipid flip-flop in a membrane preserves

A) membrane fluidity.
B) membrane melting temperatures.
C) membrane asymmetry.
D) membrane fluidity and membrane melting temperatures.
E) All of the answers are correct.

Ans: C
Section: 12.5

35) Which of the following helps regulate membrane fluidity in animals?

A) proteins
B) cholesterol
C) ATP
D) magnesium ions
E) None of the answers is correct.

Ans: B
Section: 12.5

Short-Answer Questions

36) Membranes carry out what functions due to their electrically polarized structure?
Ans: Membrane potential plays a key role in transport, energy conversion, and excitability of
neurons.
Section: Introduction

37) What are the two systems for naming the positions of the double bonds? Provide examples.
Ans: One system refers to the double bond relative to the last, or omega (), carbon. (An
example would be -3 fatty acids.) The other system uses notation that indicates the position of
the double bond relative to the carboxyl carbon, and indicates if the bond is cis or trans. (An
example would be cis-9.)
Section: 12.1

38) What are some molecules that form the polar head group of a phospholipid (bound to the
phosphate)? Provide several examples.
Ans: Examples of head groups include serine, ethanolamine, choline, glycerol, and inositol.
Section: 12.2

39) What are the primary structural differences between phospholipids constructed from a
glycerol platform and those from sphingosine?
Ans: Phospholipids derived from glycerol are called phosphoglycerides and consist of a
glycerol backbone to which are attached two fatty-acid chains and a phosphorylated alcohol.
Sphingomyelin is a phospholipid derived from sphingosine, an amino alcohol. The sphingosine
backbone is linked to a fatty acid by an amide bond and the primary hydroxy group of
sphingosine is esterified to phosphorylcholine.
Section: 12.2

40) Draw a cross-section of a micelle and a membrane bilayer.

Ans: Micelles are spherical arrangements in which the tails are on the inside of the sphere, and
the heads are on the outside surface. Bilayers have two lipid layers, in which the heads are on the
outside, and the tails are arranged on the inside in two rows. Figures 12.9 and 12.10 in the
textbook provide an example of this.
Section: 12.3

41) Draw and label a typical phospholipid.

Ans: The phospholipid drawn should resemble Figure 12.3 in the textbook. It should contain a
central glycerol molecule, to which two fatty acids are attached in ester linkages at the center and
an end. The other end should be linked to a phosphoryl-alcohol group. The phosphate should be
shown negatively charged at pH 7, and may or may not be bound to an additional head group as
shown below.
O
H H O CH2 O C(CH2)14CH3
CH3(CH2)7C C(CH2)7C O CH O
+
CH2 OPOCH2CH2N(CH3)3
O-
Section: 12.2

42) How are lipid bilayers formed? What is/are the driving forces?
Ans: Bimolecular sheets of lipids form spontaneously by self-assembly. Hydrophobic
interactions are the primary driving force. van der Waals attractive forces between the
hydrocarbon tails favor the close packing of the tails. The polar heads are attracted to each other
by electrostatic and hydrogen-bonding attractions.
Section: 12.3

43) Why do most phospholipids preferentially form sheets instead of micelles?

Ans: The two tails of phospholipids sterically hinder the formation of micelles.
Section: 12.3

44) What are liposomes? What are some of the current commercial applications?
Ans: Liposomes are spherical structures of lipid bilayers, similar to miniature organelles. They
are extremely useful as models of cell systems. They can be used to contain or transport
molecules such as drugs for therapy, DNA for gene therapy, and are commonly used in cosmetics
such as skin creams.
Section: 12.3

45) Explain the relationship between the endoplasmic reticulum and the nuclear membrane and
one additional characteristic about the nuclear membrane that sets it apart from other
membranes.
Ans: The nuclear membrane and endoplasmic reticulum are continuous; the latter is an out-
growth of the former. The nuclear membrane also contains pores through which large charged
macromolecules can pass.
Section: 12.6

46) Draw a bilayer membrane that has both an integral and peripheral protein present.
Ans: The membrane should be depicted as a bilayer, with the head groups indicated by small
balls, and the alkyl chains represented by long tails. The peripheral membrane proteins would be
loosely attached to the outside of the membrane, and the integral proteins would be shown
traversing the membrane. Figure 12.16 in the textbook provides an example of this.
Section: 12.4

47) What is the function of prostaglandin H2 synthase-1? How does its position in the membrane
facilitate its activity?
Ans: Prostaglandin H2 synthase-1 converts arachidonic acid into prostaglandin H2. The protein
is embedded in the membrane, with a hydrophobic channel submerged about halfway through
the bilayer. The arachidonic acid is a product of membrane lipid hydrolysis and enters the protein
channel from within the membrane, successfully avoiding any interaction with aqueous
environments.
Section: 12.4
48) Eukaryotic cells are distinguished from prokaryotic cells by the presence of membranes
inside the cell that form internal compartments. What are some examples?
Ans: Peroxisomes play a major role in the oxidation of fatty acids. Mitochondria are organelles
in which ATP is synthesized. The nucleus is a double membrane that consists of a set of closed
membranes that come together at nuclear pores. The endoplasmic reticulum’s roles include drug
detoxification and modification of proteins for secretion.
Section: 12.5

49) What is receptor-mediated endocytosis?

Ans: Receptor-mediated endocytosis is a transport process in which a protein is recognized by
a receptor on the cell surface and then that region of the membrane invaginates into the cell.
Section: 12.6

50) Draw the structure of sphingomyelin, and label the linkages in this structure.
Ans: See Figure 12.6
OH
H H O CHCH CH(CH2)12CH3
CH3(CH2)7C C(CH2)7C NH CH O
CH2OPOCH2CH2N(CH3)3
amide link to oleic acid O-

phosphoester to choline
phosphoester to sphingosine

Section: 12.3
Chapter 13 Membrane Channels and Pumps

Multiple-Choice Questions

1) What type of membrane transporter moves two species in opposite directions across a
membrane?

A) symporter
B) antiporter
C) uniporter
D) cotransporter
E) None of the answers is correct.

Answer: B
Section: 13.3

2) What membrane proteins allow specifically charged species to flow freely across a
membrane?

A) aquaporins
B) sodium potassium ATPase
C) glucose transporter
D) ion channels
E) None of the answers is correct.

Answer: D
Section: Introduction

3) What amino acid residue receives a phosphoryl group from P-type ATPases?

A) serine
B) tyrosine
C) cysteine
D) lysine
E) aspartate
Answer: E
Section: 13.2

4) Which of the following is a plant extract of steroids used to treat heart failure?

A) digitalis
B) nitroglycerin
C) St. John’s wort
D) salicylic acid
E) warfarin

Answer: A
Section: 13.2

5) What family of transport proteins possesses a separate domain or cassette that specifically
binds ATP?

A) glucose transporters
B) Na+-K+ ATPase
C) ABC proteins
D) bicarbonate transporters
E) None of the answers is correct.

Answer: C
Section: 13.2

6) What is the general term for membrane transporters that couple uphill transport of one
species to the downhill flow of another species?

A) cotransporters
B) antiporters
C) symporters
D) uniporters
E) None of the answers is correct.

Answer: A
Section: 13.3
7) What technique is used to measure conductance across a membrane?

A) osmotic flow analysis

B) electron crystallography
C) stop-flow
D) patch-clamp
E) None of the answers is correct.

Answer: D
Section: 13.4

8) What is another name for a nerve impulse?

A) action impulse
B) action potential
C) ion potential
D) ion impulse
E) None of the answers is correct.

Answer: B
Section: 13.4

9) What are passages that exist between adjacent cells that allow movement of ions and
small molecules?

A) gap interchanges
B) gap exchanges
C) gap crossings
D) gap intersections
E) gap junctions

Answer: E
Section: 13.5

10) In a cell-to-cell junction, 12 molecules of what protein form the gap junction?
A) actin
B) keratin
C) connexin
D) tubulin
E) None of the answers is correct.

Answer: C
Section: 13.5

Fill-in-the-Blank Questions

11. The specific transport of a species down its concentration gradient is referred to as
_______________________.
Ans: passive transport or facilitated diffusion Section: Introduction, 13.1

12. Membrane pumps ____________________(consume, produce, or transduce) energy.

Ans: transduce Section: Introduction

13. Inorganic ions and most metabolites can flow between the interiors of cells joined by
_______________.
Ans: gap junctions Section: 13.5

14. Cardiotonic steroids such as digitoxigenin inhibit the _______________________.

Ans: Na+-K+ ATPase pump Section: 13.2

15. A P-glycoprotein transporter is also referred to as MDR protein, which is an acronym for
_________________________.
Ans: multidrug-resistance Section: 13.2

16. The lactose permease transports lactose into the cell along with a(n) ______________.
Ans: H+ (proton) Section: 13.3

17. ABC transporters utilize ____________ to accomplish active transport.

Ans: ATP Section: 13.2

18. Tetrodotoxin, isolated from puffer fish, binds tightly and specifically to ___________
channels in nerve cells.
Ans: Na+ (sodium) Section: 13.4
 19. The acetylcholine receptor is an example of a ____________-gated channel.
Ans: ligand Section: 13.4

20. ___________________ are an important class of channels that increase the rate at which
water flows through membranes.
Ans: Aquaporins Section: 13.6

Multiple-Choice Questions

21) A channel that opens in response to binding a particular molecule is called a ________
channel.

A) passive diffusion
B) symport
C) ligand-gated
D) ABC-protein
E) None of the answers is correct.

Ans: C
Section 13.4

22) Channels that open in response to membrane depolarization are called __________ channels.

A) voltage-gated
B) symport
C) ligand-gated
D) ion-gated
E) None of the answers is correct.

Ans: A
Section 13.4

23) When an uncharged molecule moves from a concentration of 104 M to 102 M, is the process
spontaneous, at equilibrium, or does it require an input of energy?

A) spontaneous
B) at equilibrium
C) input of energy required
D) It depends on the membrane potential.
E) None of the answers is correct.

Ans: C
Section: 13.1

24) Which of the following is correct concerning the sarcoplasmic reticulum Ca2+ ATPase?

A) It is an example of an ABC transporter that interconverts between closed and open forms.
B) It transports Ca2+ from the sarcoplasmic reticulum into the cytoplasm.
C) This P-type ATPase maintains a calcium ion concentration of approximately 0.1 M in
the cytosol and 1.5 mM in the sarcoplasmic reticulum.
D) One Ca2+ is transported for each ATP hydrolyzed.
E) None of the answers is correct.

Ans: C
Section: 13.2

25) Multidrug resistance in tumor cells is

A) due to the action of a membrane pump that transports small molecules out of the cells.
B) the development of resistance to several drugs following an initial resistance to a single
drug.
C) caused by a mutation in the cystic fibrosis gene.
D) due to the action of a membrane pump that transports small molecules out of the cells and
the development of resistance to several drugs following an initial resistance to a single drug.
E) All of the answers are correct.

Ans: D
Section: 13.2

26) Which of the following is NOT correct concerning the ABC proteins?

A) They undergo conformational changes upon ATP binding.

B) All are also members of the P-loop NTPase superfamily.
C) The ATP-binding domains are referred to as ATP-binding cassettes.
D) They transfer a phosphate to a conserved Asp residue.
E) They are all true statements.

Ans: D
Section: 13.2
27) Membrane transporters that couple the downhill flow of one species to the uphill flow of
another species in the opposite direction are called

A) antiporters.
B) symporters.
C) exchangers.
D) P-type transporters.
E) None of the answers is correct.

Ans: A
Section: 13.3

28) Ion channels

A) can be selective.
B) exist in open and closed states.
C) in the open state often spontaneously convert into an inactivated state.
D) can be selective and exist in open and closed states.
E) All of the answers are correct.

Ans: E
Section: 13.4

29) What are the similarities between sodium, potassium, and calcium ion channels?

A) All allow passage of multiple different ions.

B) They contain homologous domains in the membrane spanning regions.
C) They all contain voltage-sensing segments that close the channel in response to a
particular membrane potential.
D) They are capable of moving ions in both directions across a membrane.
E) None of the answers is correct.

Ans: B
Section: 13.4

30) As potassium moves through the ion channel, the associated water molecules

A) are shed.
B) remain bound.
C) are rearranged around the ion.
D) react with CO2.
E) None of the answers is correct.

Ans: A
Section: 13.4

31) How does the potassium channel maintain selectivity for potassium versus sodium ions?

A) The ion size is the determining factor.

B) The size of the ion and associated waters relative to the pore size are the determining
factors in channel selectivity.
C) Dehydration of the potassium ion is compensated energetically by interactions with
oxygen atoms in the selectivity filter, which is not possible with sodium ions.
D) Potassium ions associate with six molecules of water while sodium associates with four,
thus allowing selectivity.
E) None of the answers is correct.

Ans: C
Section: 13.4

32) Aquaporins are found in high levels in all of the following tissues except

A) the kidneys.
B) salivary glands.
C) the cornea.
D) red blood cells.
E) the liver.

Ans: E
Section: 13.6

33) What is the function of selectivity filter amino acids in an ion channel?

A) They close the channel pore after ion passage.

B) They determine the preference for a particular ion.
C) They limit the number of ions passing through the channel.
D) They make sure that only positively charged ions move through the channel
E) None of the answers is correct.

Ans: B
Section: 13.4
34) In the potassium ion channel, which of the following is critical in the function of the
selectivity filter?

A) The K+ binds to a critical Glu residue.

B) The K+ binds to the amide groups of three residues in the selectivity filter.
C) The K+ binds to the carbonyl groups of the backbone of a conserved pentapeptide
sequence.
D) An ATP molecule must be bound for the selectivity filter to operate.
E) None of the answers is correct.

Ans: C
Section: 13.4

35) What clues provided evidence of the mechanism of channel inactivation?

A) Trypsin digestion of the cytoplasmic side caused the channel to stay open.
B) Protein mutants have different inactivation kinetics.
C) Inactivation could be restored by the addition of part of a missing peptide.
D) A and B
E) All of the answers are correct.

Ans: E
Section: 13.4

36) Which of the following are true about gap junctions?

A) They are important for intercellular communication.

B) Polar molecules smaller than 1 kDa can pass through them.
C) The channels stay open seconds to minutes.
D) All of the answers are correct.
E) None of the answers is correct.

Ans: D
Section: 13.5

37) Where are gap junctions found?

A) between nerve cells

B) in plasma membranes of apposed cells
C) in the synaptic cleft
D) between the ER and Golgi apparatus
E) None of the answers is correct.

Ans: B
Section: 13.5

Short-Answer Questions

38) Give the structure of the modified residue that is involved as an intermediate of P-type
ATPases.

Ans: β-phosphorylaspartate residue

Section: 13.2

39) What is simple diffusion? Provide an example.

Ans: In simple diffusion, molecules pass through a membrane from areas of higher to lower
concentration. Only lipophilic molecules can easily pass through the membrane. An example
would be a steroid hormone molecule.
Section: 13.1

40) How does active transport differ from passive?

Ans: In active transport, molecules must be pumped against a concentration gradient. This
movement requires the active input of energy.
Section: 13.1

41) How does energy affect the functioning of the Na+-K+ ATPase?
Ans: ATP provides the energy for this pump to function. The pump maintains the proper
cellular concentration of Na+ and K+, pumping Na+ out and K+ into the cell. Without ATP, the
pump could not function.
Section: 13.2

42) Many pumps are members of the P-type ATPases. If you discovered a new enzyme with
similar function, what reaction intermediate would help convince you that your enzyme was a
member of this family?
Ans: The members of this family transfer the phosphate from the ATP to a specific aspartyl
side-chain in the enzyme.
Section: 13.2

43) Describe the functional domains of the sarcoplasmic reticulum Ca2+ ATPase.
Ans: The protein has an integral membrane domain and a cytosolic head with three separate
domains. One of the head domains is responsible for binding ATP, another accepts the
phosphoryl group, and another appears to serve as the actuator. The membrane-spanning domain
is the site of calcium ion binding.
Section: 13.2

44) Describe the proposed mechanism of the lactose permease symporter.

Ans: 1. The cycle begins with the two halves oriented with the opening to the binding
pocket facing outside the cell. A proton from outside the cell binds to a residue (likely Glu 269)
in the permease.
2. The protonated permease binds lactose from outside the cell.
3. The structure everts to a form with the binding pocket facing inside the cell.
4. The permease releases the lactose to the inside of the cell.
5. The permease releases the proton to the inside of the cell.
6. The permease everts to the original form and completes the cycle.
Refer to Fig. 13.12
Section: 13.3

45) Describe the acetylcholine receptor shape.

Ans: The acetylcholine receptor is a tetramer of five subunits: two identical and three related
peptide chains (2,,γ,). The similarity between the subunits indicates gene duplication and
divergence. Binding of ligand appears to induce a conformational change, rotating a rod and
causing the channel to be open. It has been suggested that the pore is lined with polar residues.
Large hydrophobic amino acids may occlude the channel when it is closed.
Section: 13.4

46) Since we know that certain amino acids are likely to be found in membranes, why is it so
difficult to predict the structure of a channel protein?
Ans: A single membrane-binding domain is unlikely to form a channel large enough for the
passage of molecules. Most protein channels are made up of several subunits, or peptides, that
come together to form one unit. While the inside of the channel is polar, the outside, which is in
contact with the lipids, is hydrophobic. It is difficult to predict how different parts of subunits
will come together to form a whole unit by simple sequence examination.
Section: 13.4 and other sections
47) Why is it dangerous to eat puffer fish that are not properly prepared?
Ans: Puffer fish contain tetrodotoxin, a toxin that binds tightly to the sodium channel. As little
as 10 ng is fatal to humans.
Section: 13.4

48) If the selectivity filter binds the potassium ion tightly, how are ions released to pass
through the membrane?
Ans: The selectivity filter has four binding sites. Hydrated potassium ions can enter these
sites, one at a time, losing their hydration shells. When two ions occupy adjacent sites,
electrostatic repulsion forces them apart. Thus, as ions enter the channel from one side, other
ions are pushed out the other side.
Section: 13.4

49) What is the “ball-and-chain” model?

Ans: “Ball-and-chain” is a model of inactivation of a pore by occlusion. In this model, a group
of amino acids forms a “ball,” which is attached by a flexible peptide to the rest of the protein.
After the channel opens, the ball moves into a site that blocks the channel, thus quickly
inactivating the channel function.
Section: 13.4

50) Why are gap junctions sealed when high concentrations of calcium ions and protons are
present?
Ans: These conditions are common when cells are dying or traumatized. Under these
conditions, the gap junctions close so unhealthy neighbors do not compromise the healthy cells.
Section: 13.5

51) Explain how a voltage-gated channel opens.

Ans: The voltage-gated channel is composed of segments S1S6. The pore is formed by S5
and S6, and the “voltage-sensing paddles” that close the channel are composed of S1S4. The
paddles lie in the “down” position below the closed channel. Membrane depolarization pulls
these paddles through the membrane, opening the channel.
Section: 13.4; Figure 13.23

52) What is in the structure of aquaporin that prevents the transport of ions as well as water?
Ans: Two loops containing hydrophilic residues line the channel, facilitating the movement of
water molecules. Specific charged residues toward the center of the channel prevent transport of
protons.
Section: 13.6
Chapter 14 Signal-Transduction Pathways

Multiple-Choice Questions

1) What is the primary messenger that is released by the adrenal gland?

A) dopamine
B) epinephrine
C) glucagon
D) insulin
E) acetylcholine

Answer: B
Section: Introduction and 14.1

2) Which of the following is another name for a seven-transmembrane helix receptor?

A) tyrosine kinase receptor

B) ion channel receptor
C) enzyme-linked receptor
D) β-adrenergic receptor
E) None of the answers is correct.

Answer: D
Section: 14.1

3) What is covalently attached to the  and  subunits of heterotrimeric G proteins in order

to anchor the protein to the cell membrane?

A) galactose
B) N-acetylgalactosamine
C) cholesterol
D) phosphatidyl serine
E) fatty acid

Answer: E
Section: 14.1

4) What enzyme becomes active when bound to Ca2+ and diacylglycerol?

A) calmodulin
B) protein kinase A
C) protein kinase C
D) phospholipase C
E) adenylate cyclase

Answer: C
Section: 14.1

5) Which of the following is the inactive form of protein kinase A?

A) R2C2
B) R4C2
C) R2C4
D) R4C4
E) None of the answers is correct.
Section: 14.1

Answer: A

6) What family of proteins contains the Ras proteins?

A) GAP proteins
B) G-protein receptor kinases
C) small G proteins
D) seven-transmembrane helix receptors
E) heterotrimeric G proteins

Answer: C
Section: 14.3
7) What is a gene that leads to the transformation of susceptible cell types into cell types
with cancer-like characteristics?

A) protogene
B) retrogene
C) epigene
D) oncogene
E) None of the answers is correct.

Answer: D
Section: 14.5

8) What eukaryotic protein serves as an intracellular Ca2+ sensor by binding to four calcium
ions?

A) calmodulin
B) phospholipase C
C) protein kinase C
D) vitamin D-dependent calcium binding protein
E) calcitonin

Answer: A
Section: 14.1

9) What is a gene that contributes to cancer development only when deleted or damaged?

A) oncogene
B) proto-oncogene
C) viral oncogene
D) carcinoma-suppressor gene
E) tumor-suppressor gene

Answer: E
Section: 14.5

10) What enzyme catalyzes the cleavage of PIP2?

A) phospholipase A
B) phospholipase C
C) phospholipase D
D) phospholipase P
E) None of the answers is correct.

Answer: B
Section: 14.1

Fill-in-the-Blank Questions

11. Protein kinase A phosphorylates serine and ___________ residues.

Ans: threonine Section: 14.1

12. ____________ is the membrane protein that catalyzes the conversion of ATP to cAMP.
Ans: Adenylate cyclase Section: 14.1

13. The cytosolic side, or β subunit, of the insulin receptor is a ________________ kinase.
Ans: tyrosine Section: 14.2

14. The ________ receptor is approximately 50% identical in amino acid sequence with the
EGF receptor and has similar domain structure, but it does not bind any known ligand.
Ans: HER2 Section: 14.3

15. Important second messengers include cAMP, cGMP, calcium ion,

_______________________, and diacylglycerol.
Ans: inositol 1,4,5-trisphosphate (IP3) Section: Introduction

16. Input from several signaling pathways is called _____________________.

Ans: cross talk Section: 14.1 and 14.4

17. _______________________ binds to the extracellular side of β-adrenergic receptors.

Ans: Epinephrine Section: 14.1

18. The binding of IP3 to the IP3 receptor results in the release of __________ from the
endoplasmic reticulum.
Ans: calcium ions Section: 14.1

19. The catalytically active form of the insulin receptor is a result of phosphorylation of
specific ____________ residues in the activation loop.
Ans: tyrosine Section: 14.2
 20. EGF signaling is terminated by the action of phosphatases and the hydrolysis of bound
_____________ by Ras.
Ans: GTP Section: 14.3

Multiple-Choice Questions

21) Most signal molecules

A) easily diffuse through the membrane and bind to a receptor in the cytoplasm.
B) bind to membrane receptors and transmit information across a membrane without
traversing the membrane.
C) carry out functions in the nucleus after binding to a receptor in the cell membrane.
D) easily diffuse through the membrane and bind to a receptor in the nucleus.
E) None of the answers is correct.

Ans: B
Section: Introduction

22) Examples of second messengers include

A) cAMP.
B) calcium.
C) inositol 1,4,5-trisphosphate.
D) cGMP.
E) All of the answers are correct.

Ans: E
Section: Introduction

23) Advantages of second messengers include

A) the signal can be amplified by making many second messengers.

B) second messengers can freely diffuse to other sites within the cell.
C) a few common second messengers can be used in multiple signaling pathways.
D) All of the answers are correct.
E) A and C.

Ans: D
Section: Introduction
24) Which of the following amino acids can be phosphorylated?

A) Tyr, Ser, Thr

B) Tyr, Ser, Trp
C) Ser, Thr, Asn
D) His, Ser, Phe
E) Tyr, Met, Trp

Ans: A
Section: 14.1

25) Which form of the guanyl nucleotide is bound to a G protein in its unactivated state?

A) GTP
B) GDP
C) GMP
D) dGTP
E) None of the answers is correct.

Ans: B
Section: 14.1

26) Which of the following is a common example of a mechanism by which a signaling process
might be terminated?

A) change in temperature
B) aggregation of all protein subunits
C) protein dephosphorylation by phosphatases
D) All of the answers are correct.
E) None of the answers is correct.

Ans: C
Section: 14.1

27) How does the binding of epinephrine to its receptor set a response in action?

A) It causes an exchange of GTP for G protein bound GDP.

B) It causes a pore to open, allowing proton/ion exchange.
C) It causes the release of insulin.
D) It causes G proteins to produce cGMP.
E) None of the answers is correct.

Ans: A
Section: 14.1

28) Why is bound GTP considered a “clock”?

A) It is always produced and degraded in specific time intervals.

B) It is regulated by energy.
C) The G receptors have intrinsic GTPase activity, hydrolyzing GTP to GDP and Pi.
D) It spontaneously hydrolyzes in the binding site of G proteins.
E) None of the answers is correct.

Ans: C
Section: 14.1

29) The enzyme responsible for induction of the phosphoinositide cascade is

A) phospholipase C.
B) phospholipase A.
C) C-dependent protein (CDP).
D) calmodulin.
E) None of the answers is correct.

Ans: A
Section: 14.1

30) Common elements that occur in many signal transduction pathways include which of the
following?

A) Specialized domains mediate specific interactions in the pathway.

B) Second messengers may participate.
C) Cell division is usually the result.
D) A and B
E) All of the answers are correct.

Ans: D
Section: 14.4

31) How is calmodulin activated?

A) by binding both calcium and potassium
B) by binding Ca2+ when the cytosolic concentration is greater than 500 nM
C) by binding to a positively charged helix on another protein
D) by binding Ca2+ only when calcium channels are open, allowing Ca2+ efflux from the cell
E) None of the answers is correct.

Ans: B
Section: 14.1

32) Cross-phosphorylation of the EGF receptor is possible when two receptor proteins

A) are cleaved.
B) dimerize.
C) are internalized into organelles.
D) covalently cross link.
E) None of the answers is correct.

Ans: B
Section: 14.2 and 14.3

33) Which of the following is an example of a disease that is caused by altered G-protein
activity?

A) whooping cough
B) cholera
C) bubonic plague
D) whooping cough and cholera
E) whooping cough and bubonic plague

Ans: D
Section: 14.5

34) ______________ may be effective anti-cancer drugs.

A) Monoclonal antibodies against offending receptors

B) EGF mimics
C) Protein kinase inhibitors
D) All of the answers are correct.
E) Both monoclonal antibodies against offending receptors and protein kinase inhibitors
Ans: C
Section: 14.5
35) The v and c in v-src and c-src refer to

A) viral and cellular.

B) viral and cytosolic.
C) viral and cystic.
D) Vibrio and cholera.
E) None of the answers is correct.

Ans: A
Section: 14.5

Short-Answer Questions

36) What are some of the common structural features of the receptors to which signal molecules
bind?
Ans: The molecule must have a signal-binding site on the extracellular side of the membrane
and must have an intracellular domain. Binding of the ligand to the receptor must induce change
into another form that affects the shape of the intracellular portion, so the signal can be
transmitted.
Section: Introduction

37) What is a disadvantage of using common molecules for signaling paths?

Ans: When second messengers are involved in more than one signaling pathway, fine tuning
and sensitive responses can result. However, when the cross-talk becomes inappropriate, the
signaling paths and responses will be in error.
Section: Introduction

38) What happens when signaling paths are not terminated properly?
Ans: The cell will not be able to respond properly to new stimuli. The errant signals may lead
to cancer, especially if there is uncontrolled cell growth.
Section: Introduction

39) How many 7TM membranes exist? What are some of their functions?
Ans: There are estimated to be thousands of 7TM receptors. Functions they mediate include
sensory signaling, physiological control, exocytosis, chemotaxis, neurotransmission, cell
development and growth, and viral infection. (See Table 14.1 of the textbook for a more
complete list.)
Section: 14.1
40) What is the general mechanism for signal transmission by 7TM receptors?
Ans: The receptors “snake” through a membrane, with domains extending on the extracellular
and cytoplasmic sides. A ligand binds to a site on the extracellular side, inducing a conformation
change that is detectable on the cytoplasmic side of the cell.
Section: 14.1

41) How does binding of epinephrine initiate cAMP production? Discuss briefly in terms of
receptor structure and function.
Ans: Epinephrine binds to a 7TM receptor which interacts with heterotrimeric G protein,
causing it to exchange GDP with GTP. The binding of GTP causes the G protein to dissociate
and the active Gα – GTP complex binds to the enzyme, adenylate cyclase. Adenylate cyclase is a
large membrane-embedded protein, with two large domains located on the inside of the cell. This
interaction induces a conformational change in the enzyme resulting in a more catalytically
active form, thus more cAMP is made. (See Figure 14.8 of the textbook for more detail.)
Section: 14.1

42) How is the hormone-bound activated receptor reset after activation?

Ans: The hormone dissociates, and the receptor returns to its initial state. In addition,
phosphorylation of specific residues leads to the binding of β–arrestin, which further diminishes
its ability to activate G proteins.
Section: 14.1

43) What are receptor tyrosine kinases? Provide an example.

Ans: These are proteins that bind ligands, such as EGF or insulin, on the extracellular domain.
They also contain tyrosine kinase domains on the intracellular side.
Section: 14.1 and 14.2

44) What is the difference between an oncogene and a proto-oncogene?

Ans: An oncogene, such as v-src, leads to the generation of cancer-like characteristics in
susceptible cell types. A proto-oncogene, such as c-src, does not induce cell transformation but
refers to the fact that this gene, when mutated, can be converted into an oncogene.
Section: 14.5

45) In addition to its range in concentration, what other property of calcium ion makes it a highly
suitable messenger?
Ans: It can bind tightly to proteins because it forms between six and eight interactions with
protein ligands or water. These extensive interactions allow calcium ions to mediate large
conformational changes in proteins.
Section: 14.1

46) What is meant by an EF hand? Draw or describe the structure.

Ans: The EF hand is a protein that binds calcium ions and contains a calcium ion-binding
domain that contains a helix-loop-helix arrangement. The structure resembles a hand, index
finger and thumb extended, with the ion held near the palm by the middle finger. Figure 14.17 of
the textbook is an example of what a drawing of this structure may look like.
Section: 14.2

47) Draw the reaction catalyzed by tyrosine kinase (no mechanism necessary).
Ans:
OH O PO3-2
ATP ADP

Tyrosine
H H
kinase
H C H C
N N
O O
Section: 14.2

48) What is the relationship between monoclonal antibodies, breast cancer, and HER2?
Ans: HER2 is a membrane protein that is very similar to the EGF receptor protein except it
does not bind any known ligand. It can participate in cross-phosphorylation reactions with other
receptors activating signaling pathways such as the EGF pathway. HER2 is overexpressed in
about 30% of breast cancers. Monoclonal antibodies to HER2 have been used to treat cancers in
these patients.
Section: 14.3, 14.5

49) What is the difference between heterotrimeric G proteins and small G proteins?
Ans: Heterotrimeric G proteins are composed of αβγ subunits. The α subunit contains the
guanyl nucleotide binding site. Upon activation by the signal-receptor event, the GDP is
exchanged with a GTP, and the βγ subunits dissociate from the α bound with GTP. The resulting
Gα is the form that activates adenyl cyclase. Small G proteins, such as Ras, are single subunit
proteins. They are activated by proteins such as Sos in the EGF signal pathway, which allows
GTP to replace GDP, converting Ras into its activated form.
Section: 14.1 and 14.3

50) Describe two roles of phosphatidylinositol 4,5-bisphosphate (PIP2) in signal transduction.

Ans: 1. PIP2 is one of the signal molecules in the insulin pathway. It is converted into PIP3 by
phosphoinositide 3-kinase. The binding of PIP3 activates PIP3-dependent protein kinase, which
phosphorylates and activates other kinases in the insulin pathway. 2. PIP2 is also involved in
another signal pathway that is activated by angiotensin II. The angiotensin II receptor activates
phospholipase C, which hydrolyses PIP2 to produce diacylglycerol (DAG) and inositol 1,4,5-
trisphosphate (IP3). The DAG binds to and activates protein kinase C (PKC), and the IP3 binds to
an IP3 receptor in the endoplasmic reticulum that is also a calcium ion channel. This opens the
channel and calcium ions are released into the cytoplasm. The calcium ions bind to PKC and
facilitate its activation.

Section 14.1