Sample Chapter



Biochemistry 7th Edition by Campbell – Test Bank





Chapter 1   Biochemistry: An Evolving Science



Matching Questions

Use the following to answer questions 1-10:


Choose the correct answer from the list below. Not all of the answers will be used.

  1. a) uridine
  2. b) true
  3. c) DG
  4. d) thymine
  5. e) DH
  6. f) sugar-phosphate units
  7. g) covalent
  8. h) Archaea
  9. i) entropy
  10. j) system
  11. k) 3
  12. l) 2
  13. m) false


1. DNA is made from the building blocks adenine, guanine, cytosine, and ____________.


Ans: d
Section:  1.2


2. The DNA backbone is made from repeating ____________.


Ans: f
Section:  1.2


3. ____________ The number of hydrogen bonds formed between A and T.


Ans: l
Section:  1.2


4. ____________ The number of hydrogen bonds formed between G and C.


Ans: k
Section:  1.2


5. The fundamental groups of organisms include Eukarya, Bacteria, and ____________.


Ans: h
Section:  1.1


6. ____________ The strongest bonds in molecules:


Ans: g
Section:  1.3


7. ____________ Hydrogen bonds are usually weaker than covalent bonds (true/false).


Ans: b
Section:  1.3


8. ____________ Matter within a defined region of space.


Ans: j
Section:  1.3


9. ____________ For spontaneous reactions the DG must be positive (true/false).


Ans: m
Section:  1.3


10. ____________ Gibbs-free energy.


Ans: c
Section:  1.3



Multiple-Choice Questions












Which of the following is considered a metabolite, a substance that is chemically transformed in a biochemical process?

A)     deoxyribonucleic acid

B)     glycerol

C)     protein

D)     ribonucleic acid

E)     polysaccharide

Ans:   B     Section: 1.1


The structure of DNA described by Watson and Crick included

A) a double helix.
B) the sugar phosphate backbone aligned in the center of the helix.
C) the base pairs that are stacked on the inside of the double helix.
D) a and b.
E) a and c.
Ans:  E     Section:  1.2
13. What did Watson and Crick suggest to be significant about the base pairing found in the helix?
A) It allowed the DNA to twist in a helix.
B) The DNA could be circular.
C) It was a mechanism for copying.
D) All of the above.
E) None of the above.
Ans:  C     Section:  1.3


14. Approximately what percentage of the human genome encodes for proteins?
A) 50%
B) 90%
C) 10%
D) 3%
E) None of the above.
Ans:  D     Section: 1.4


15. What gives proteins such a dominant role in biochemistry?
A) the rigidity of the peptide backbone
B) the ability to act as a blueprint
C) their ability to self-replicate
D) their ability to spontaneously fold into complex three-dimensional structures
E) All of the above.
Ans:  D     Section:  1.4


16. If the whole chain is used in a non-overlapping frame, how many amino acids are defined by this DNA sequence: ATGTTTGGACTA?
A) four     B) two     C) twelve     D) six     E) three
Ans:  A     Section:  1.4


17. What is the [H+] concentration in a urine sample that has a pH of 6?
A) 10-6 M
B) 10-8 M
C) 106 M
D) 10-14 M
E) 8 M
Ans:  A     Section 1.3


18. Which is the correct order of increasing bond energies?
A) hydrogen bonds, covalent bonds, van der Waals interactions D) covalent bonds, hydrogen bonds, van der Waals interactions
B) hydrogen bonds, electrostatic interactions, covalent bonds E) hydrophobic interactions, hydrogen bonds, electrostatic interactions
C) van der Waals interactions, covalent bonds, hydrogen bonds
Ans:  D     Section:  1.3


19. The energies for hydrogen bonds are approximately
A) 400 kJ/mol. D) 200 kJ/mol.
B) 100–240 kJ/mol. E) None of the above.
C) 4–20 kJ/mol.
Ans:  C     Section:  1.3


20. What pairs of atoms in bases are involved in hydrogen bonds?
A) N—H and O—H D) All of the above.
B) N—H and S—H E) None of the above.
C) O—H and P—O
Ans:  A     Section:  1.3


21. Typical van der Waals energies are about
A) 4–20 kJ/mol. D) All of the above.
B) 2–4 kJ/mol. E) None of the above.
C) 200 kJ/mol.
Ans:  B     Section:  1.3


22. What two properties of water are important for biological interactions?
A) the polarity of water D) a and c
B) the density of water E) b and c
C) the cohesive properties of water
Ans:  D     Section:  1.3


23. The First Law of Thermodynamics states
A) diversity is the result of gradual evolution.
B) the total entropy of a system and its surroundings always increase for a spontaneous process.
C) the total energy of a system and its surroundings are constant.
D) light is both particle and wave.
E) None of the above.
Ans:  C     Section:  1.3


24. The Second Law of Thermodynamics states
A) the total entropy of a system and its surroundings always increase for a spontaneous process.
B) temperatures will always decrease.
C) the total energy of a system and its surroundings are constant.
D) diversity is the result of gradual evolution.
E) None of the above.
Ans:  A     Section:  1.3


25. List atoms commonly found in biological molecules that are often hydrogen-bond donors.
A) carbon     B) oxygen     C) nitrogen     D) b and c     E) All of the above.
Ans:  D     Section:  1.3


26. Entropy is defined as
A) a spontaneous reaction. D) All of the above.
B) the enthalpy of the system. E) None of the above.
C) the measure of randomness of a system.
Ans:  C     Section:  1.3


27. If a particular reaction has a negative DG, is it likely to occur?
A) Not unless energy is added to the system.
B) Yes, if it is coupled to another reaction.
C) Yes, it is spontaneous.
D) No, it is not spontaneous.
E) Yes, if it takes place within a constrained area.
Ans:  C     Section:  1.3


28. What happens to nonpolar molecules in water?
A) They dissolve independently. D) All of the above.
B) They aggregate together. E) None of the above.
C) They precipitate.
Ans:  B     Section:  1.3


29. What is the [A]/[HA] ratio when the weak acid is in a solution one pH unit below its pKa?
A) 1:1 D) 2:1
B) 1:10 E) None of the above.
C) 10:1
Ans:  B     Section 1.3


30. Why does DNA denature when the pH is raised above 9?
A) Protons dissociate from guanine bases disrupting the hydrogen bonding to the other strand.
B) Protons bind to guanine residues giving them additional positive charges which disrupt the hydrogen bonding to the other strand.
C) Protons bind to functional groups that serve as hydrogen-bond acceptors, thus disrupting the hydrgogen bonding to the other strand.
D) Protons dissociate from the phosphate groups in the backbone, which disrupts the hydrogen-bonding pattern between strands.
E) None of the above.
Ans:  A     Section 1.3


31. Stereochemistry can be easily depicted in a simple form using
A) ball-and-stick models. D) Fisher projections.
B) ribbon diagrams. E) None of the above.
C) space-filling models.
Ans:  D     Section:  Appendix


32. Using the Henderson–Hasselbach equation, calculate the pH of a buffer solution made from 0.20 M HC2H3O2 and 0.050 M C2H3O2 that has  pKa= 4.7.
A) 4.3 D) 0.4
B) 5.1 E) None of the above.
C) 2.5
Ans:  B     Section 1.3


33. What are the primary chemical components present in a phosphate buffer at pH 7.4?
A) H3PO4 and PO4-3 D) H2PO4 and HPO4-2
B) H2PO4 and PO4-3 E) H3PO4 and HPO4-2
C) HPO4-2 and PO4-3
Ans:  D     Section 1.3



Short-Answer Questions


33. What are some of the medical implications of the human genome project?
Ans: The obvious use is in diagnosing disease and in developing methods to treat and cure diseases. Physicians will be able to account for individual genetic differences in determining the best medical treatment.
Section:  Introduction


34. What is the significance of hydrogen bonding in biochemical structures such as DNA?
Ans: The bonds are weak enough to be easily disrupted; yet when many are present, they provide the stabilization necessary for larger structures such as DNA.
Section:  1.2


35. What adaptation affected evolutionary diversity?
Ans: Alteration of biochemical molecules and components to new roles is key to diversity and evolution.
Section:  1.1


36. Describe resonance structures.
Ans: Resonance structures are ways of writing covalent bonds in which two or more alternate bonding patterns can be achieved. This is due to the sharing of electrons over several atoms. Common examples are found in peptide bonds, and in some of the bases. Benzene is shown in the text.
Section:  1.3


37. What is significant about the fact that metabolic processes are common to many organisms?
Ans: These metabolic processes are extremely old, geologically, originating in a common ancestor.
Section:  1.1


38. How is water able to be a solvent for so many biological molecules?
Ans: Many biological molecules have polar characteristics. Water is extremely polar and is capable of competing with other polar molecules by weakening their electrostatic and hydrogen bonds. The oxygen can act as a hydrogen-bond acceptor, and the hydrogen can act as a donor.
Section:  1.3


39. What is the net effect of many van der Waals interactions?
Ans: At the interface of two large molecules, the numerous van der Waals interactions can substantially affect and stabilize the interaction.
Section:  1.3


40. If most proteins are found surrounded by water in the cell, what type of functional groups would you expect to find on the surface of a water-soluble protein?
Ans: Polar and charged amino-acid residues would be present on the surface of the protein.
Section:  1.3


41. How are electrostatic forces used in protein folding?
Ans: The attraction of two oppositely charged functional groups would be one of the forces helping to form the three-dimensional shape of the protein.
Section:  1.3


42. If the First Law of Thermodynamics is true, how can biological processes be carried out?
Ans: Although energy cannot be created or destroyed, it can take on different forms, such as heat or chemical energy. Thus, the energy can be stored as chemical bond energy, which can be used to do work.
Section:  1.3


43. How can a cell exist if the Second Law of Thermodynamics is true?
Ans: Entropy in a local area can be decreased, but only at the expense of increased entropy in the larger area, or universe.
Section:  1.3


44. Provide a simple example of entropy processes.
Ans: Several examples can be provided, including the random mixture of atoms when two different gases are mixed, or the creation of water molecules from energy gained following the mixture of oxygen and hydrogen under certain conditions.
Section:  1.3


45. When solutions containing complementary single strands of DNA are mixed, a loss of entropy occurs. How is it that the Second Law of Thermodynamics is not violated?
Ans: Heat must be released to the surroundings.
Section:  1.3


46. What is the significance of using DG in biochemistry?
Ans: Gibbs-free energy, also called the free-energy change, is used to describe the energetics of a reaction. This symbol is used to determine if particular reactions will be spontaneous or biologically feasible.
Section:  1.3


47. What thermodynamic and free-energy changes participate in protein folding?
Ans: A combination of hydrogen bonds and van der Waals forces affect enthalpy and the entropy associated with hydrophobic interactions.
Section:  1.3


48. How do hydrophobic interactions aid in protein folding?
Ans: Hydrophobic interaction causes some nonpolar amino acids to aggregate and form the interior of the protein. This results in a net release of heat and a favorable change in the system enthalpy.
Section:  1.4


49. What are the enthalpy and entropy changes that accompany the formation of DNA double helixes from complementary single strands of DNA?
Ans: There is a loss of entropy from the system because there are fewer degrees of freedom in the double helix as compared to the single strands.  Therefore, heat must be released when the two strands combine to form the double helix so as not to violate the Second Law of Thermodynamics.
Section: 1.3


50. Describe the shape of methane.
Ans: Methane is tetrahedral and sp3 hybridized, with bond angles of about 109°.
Section:  Appendix


Chapter 2   Protein Composition and Structure



Matching Questions

Use the following to answer questions 1-10:


Choose the correct answer from the list below. Not all of the answers will be used.

  1. a) l-amino acids
  2. b) water
  3. c) protons
  4. d) Zwitterions
  5. e) secondary structure
  6. f) tertiary structure
  7. g) Ramachandran
  8. h) cysteine
  9. i) extracellular
  10. j) histidine
  11. k) proline
  12. l) Sanger
  13. m) d-amino acids


1. ____________ Chiral type of amino acids found in proteins.


Ans: a
Section:  2.1


2. ____________ Another name for dipolar molecules.


Ans: d
Section:  2.1


3. ____________ Disulfide bonds are formed by pairs of which amino acid?


Ans: h
Section:  2.1


4. ____________ The amino acid with a pKa near neutral pH.


Ans: j
Section:  2.1


5. ____________ When a peptide bond is formed, what molecule is also made?


Ans: b
Section:  2.2


6. ____________ Where are proteins with extensive disulfide links likely to be found?


Ans: i
Section:  2.2


7. ____________ This amino acid residue frequently found in β-turns.


Ans: k
Section:  2.1



8. ____________ Name of the plot that allows one to investigate the likely orientation of certain amino acid pairs.


Ans: g
Section:  2.2


9. ____________ The type of structure to which α  helices, β sheets, and turns are referred.


Ans: e
Section:  2.3


10. ____________ The overall three-dimensional structure of a protein is referred to as


Ans: f
Section:  2.4



Fill-in-the-Blank Questions


11. The amino acid that contains a sulfur atom and is consider hydrophobic  is _________________.
Ans:  methionine     Section: 2.1


12. _______________ is a fibrous protein and is the primary component of wool and hair.
Ans:  Α keratin     Section: 2.3


13. Every third residue in the protein collagen is ____________________.
Ans:  glycine     Section: 2.3


14. Disulfide bonds in proteins can be reduced to free sulfhydryl groups by reagents such as _____________________.
Ans:  β mecaptoethanol     Section: 2.6


15. A protein is considered to be __________________ when it is converted into a randomly coiled structure without its normal activity.
Ans:  denatured     Section: 2.6


16. ______________________ is the major fibrous protein present in skin, bone, tendon, cartilage, and teeth.
Ans:  Collagen     Section: 2.3


17. Collagen contains _____________________, a modified amino acid.
Ans:  hydroxyproline     Section: 2.6


18. Agents such as ______________________ and guanidine hydrochloride denature proteins by disrupting the noncovalent interactions.
Ans:  urea     Section: 2.6


19. _____________________________ refers to the spatial arrangement of subunits and the nature of their interactions
Ans:  Quaternary structure     Section: 2.5


20. The ________________________ β-sheet structure occurs when the two strands are oriented in same directions (N → C).
Ans:  antiparallel     Section:  2.3



Multiple-Choice Questions


21. Proteins function as
A) energy stores. D) None of the above.
B) catalysts. E) All of the above.
C) storage of genetic information.
Ans:  B     Section:  Introduction


22. Key properties of proteins include
A) a wide range of functional groups.
B) an ability to possess either rigid or flexible structures as dictated by functional requirements.
C) the ability to interact with other proteins.
D) a and b.
E) All of the above.
Ans:  E     Section:  Introduction


23. What charged group(s) are present in glycine at a pH of 7?
A) –NH3+     B) –COO      C) –NH2+     D) a and b     E) a, b, and c
Ans:  D     Section:  2.1


24. At a pH of 12, what charged group(s) are present in glycine?
A) -NH3+     B) -COO     C) -NH2+     D) a and b     E) a, b, and c
Ans:  B     Section:  2.1


25. What do the amino acids tyr, asn and thr have in common?
A) have aromatic rings D) contain double bonds in side chains
B) are negatively charged at pH 7.0 E) are polar
C) are positively charged at pH 7.0
Ans:  E     Section 2.1


26. Which amino acids contain a sulfur atom?
A) serine and methionine D) cysteine and methionine
B) serine and threonine E) cysteine and threonine
C) methionine and threonine
Ans:  D     Section:  2.1


27. Name three amino acids that can be positively charged at a neutral pH.
A) lys, arg, and his D) lys, arg, and pro
B) his, arg, and cys E) arg, glu, and his
C) cys, arg, and met
Ans:  A     Section:  2.1


28. In the following peptide, which amino acid is the N-terminus?


A) Ala     B) Phe     C) Phe and Arg     D) Arg     E) None of the above.
Ans:  B     Section:  2.2


29. What is the approximate mass of a protein containing 200 amino acids? (Assume there are no other protein modifications.)
A) 20,000     B) 11,000     C) 22,000     D) 222,000     E) None of the above.
Ans:  C     Section:  2.2


30. Which individual won a Nobel Prize for his landmark work in sequencing the protein insulin?
A) Pauling     B) McClintock     C) Gilbert     D) Maxam     E) Sanger
Ans:  E     Section:  2.2


31. Why is the peptide bond planar?
A) Bulky side chains prevent free rotation around the bond.
B) It contains partial double-bond character, preventing rotation.
C) Hydrogen bonding between the NH and C=O groups limits movement.
D) None of the above.
E) All of the above.
Ans:  B     Section:  2.2


32. The configuration of most α-carbon atoms of amino acids linked in a peptide bond is
A) cis.     B) circular.     C) parallel.     D) trans.     E) perpendicular.
Ans:  D     Section:  2.2



33. What structure(s) did Pauling and Corey predict in 1951?
A) α helix     B) β sheet     C) β turns     D) a, b, and c     E) a and b
Ans:  E     Section:  2.4


34. The term “quaternary” with respect to protein structure means
A) a repeating structure stabilized by intrachain hydrogen bonds.

B) the ability to form all four kinds of noncovalent bonds.

C) a multisubunit structure.

D) a linear sequence of four amino acids.

E) None of the above.

Ans:  C     Section:  2.5


35. Where are Ω and β turns and loops often found?
A) in a hydrophobic pocket D) on the surface of proteins
B) on the interior cleft E) None of the above.
C) at the protein interface with ligand
Ans:  D     Section:  2.3


36. What are some of the modifications that proteins acquire?
A) cleavage and trimming of the protein D) a, b, and c
B) addition of carbohydrate groups E) b and c
C) phosphorylation of certain groups
Ans:  D     Section:  2.6


37. Which of the following amino acid residues would most likely be buried in the interior of a water-soluble, globular protein?
A) Asp D) Lys
B) Ser E) Gln
C) Phe
Ans:  C     Section 2.5



Short-Answer Questions


38. How does a protein’s amino acid sequence influence the tertiary structure?
Ans: A protein will spontaneously fold into a three-dimensional structure determined by the amino acid sequence.
Section:  Introduction


39. What is the advantage of having 20 different amino acids available to form proteins?
Ans: The amino acids provide a rich diversity of functional groups, which can independently contribute to protein structure and function. In addition, many can be modified, increasing the diversity of functional groups.
Section:  Introduction


40. What is the advantage of protein interaction and assembly with other proteins?
Ans: When proteins interact or assemble, new functions and specificity become available. Protein interactions allow new binding sites at the assembly interface, as well as providing multifunctional activity and specificity, such as found in polymerases and signal transduction.
Section:  Introduction


41. What are the three aromatic amino acids?
Ans: phenylalanine, tyrosine, and tryptophan
Section:  2.1


42. Which amino acid side chains are capable of ionization?
Ans: The amino acids are: Asp, Glu, His, Cys, Tyr, Lys, and Arg.
Section:  2.1


43. How does the protein backbone add to structural stability?
Ans: The protein backbone contains the peptide bond, which has NH molecules and C=O (ketone) groups. Hydrogen-bond formation between the hydrogen on the nitrogen and the oxygen support the protein conformation.
Section:  2.2


44. Why are all the theoretical combinations of phi and psi not possible?
Ans: Steric hindrances of the side chains make certain combinations and angles impossible.
Section:  2.2


45. Describe some of the features of an α helix.
Ans: The α helix is coil stabilized by intrachain hydrogen bonds between the carbonyl oxygen of a residue and the amide hydrogen of the fourth residue away. There are 3.6 amino acids per turn. The hydrogen bonds are between amino acid residues that have two intervening residues.  Thus, these amino acid residues are found on the same side of the coil.  The helix is almost always right-handed, although left-handed helices are, in theory, possible.
Section:  2.3


46. What is the “hydrophobic effect” as it relates to protein structure?
Ans: The three-dimensional structure of a water-soluble protein is stabilized by the tendency of hydrophobic groups to assemble in the interior of the molecule.
Section:  2.1


47. Α Keratin is referred to as a coiled-coil protein. Describe this protein structure.
Ans: Two or more α helices can entwine to form a very stable structure of approximately 100 nm.
Section:  2.3


48. What are prions?
Ans: Prions are proteins that can assume (after infection or by other causes) a new protein structure, which is self-propagating. The disease has several variants, and at least one is fatal to humans.
Section:  2.6


49. What does the modification involving the attachment of acetyl groups to the amino termini of a protein do?
   Ans: The acetylation of the amino termini of proteins is to make these proteins more resistant to degradation.
Section:  2.6


50. In the ribonuclease experiments performed by Anfinson, what was the significance of the presence of the reducing agent β mercaptoethanol?
Ans: The reducing agent reduced incorrectly paired disulfide bonds, allowing them to reform with the correct pairing until the most stable conformation of the protein had been obtained.
Section:  2.6


51. What is the advantage of having certain regions of partially correct folded regions?
Ans: If some regions interact preferentially, lending stability to certain conformations as the protein folds, they can impact the overall structure of the protein.
Section:  2.6

Chapter 7   Hemoglobin: A Portrait of a Protein in Action



Matching Questions

Use the following to answer questions 1-10:


Choose the correct answer from the list below. Not all of the answers will be used.

  1. a) cooperative
  2. b) Bohr effect
  3. c) thalassemia
  4. d) carbamate
  5. e) metmyoglobin
  6. f) superoxide
  7. g) myoglobin
  8. h) bicarbonate ion
  9. i) sickle-cell anemia
  10. j) protoporphyrin
  11. k) fetal
  12. l) carbonic acid


1. Carbon dioxide reacts with the amino terminal groups of deoxyhemoglobin to form __________ groups.


Ans:  d
Section:  7.3



2. ____________ This is the organic portion of the heme group in hemoglobin.


Ans:  j
Section:  7.1


3. ____________ This is a genetic disease due to the decreased production of one of the subunits of hemoglobin.


Ans:  c
Section:  7.4


4. ____________ This is the chemical form in which most of the carbon dioxide is transported in the blood.


Ans:  h
Section:  7.3


5. ____________ This substance is produced when carbon dioxide reacts with water.


Ans:  l
Section:  7.3


6. ____________ This type of hemoglobin is composed of two α chains and two γ chains.


Ans:  k
Section:  7.2


7. ____________ This is the molecule whose function is to store oxygen in muscle cells.


Ans:  g
Section:  Introduction


8. ____________ This oxidized hemeprotein does not reversibly bind oxygen.


Ans:  e
Section:  7.1


9. ____________ This type of binding is indicated by a sigmoidal-shaped binding curve.


Ans:  a
Section:  7.2


10. ____________ This condition is a result of a single point mutation in the β chain of hemoglobin.


Ans:  i
Section:  7.4



Fill-in-the-Blank Questions


11. Under normal conditions, the heme iron in myoglobin and hemoglobin is in the ____________ oxidation state.
Ans:  ferrous, or Fe+2     Section:  7.1


12. The ability of myoglobin to bind oxygen depends on the presence of a bound prosthetic group called _____________.
Ans:  heme     Section:  7.1


13. In hemoglobin, the iron of the heme is bonded to the four nitrogens of porphyrin and to the proximal ______________ residue of the globin chain.
Ans:  histidine     Section:  7.1


14. The binding of 2-3-bisphosphogycerate to hemoglobin ____________ (increases, decreases) its affinity of oxygen binding.
Ans:  decreases     Section:  7.2


15. The effect of pH on oxygen-binding of hemoglobin is referred to as the _____________.
Ans:  Bohr effect     Section:  7.3


16. Deoxyhemoglobin is stabilized through ___________________ interactions between the carbamates and positively charged amino acids at the interface between αβ dimmers.
Ans:  salt-bridge     Section:  7.3


17. The T-state of hemoglobin is stabilized by a salt bridge between β1 Asp 94 and the C-terminal ___________________ of the β1 chain.
Ans:  histidine     Section:  7.3


18. In normal adult hemoglobin, HbA, the β6 position is a glutamate residue, whereas in sickle-cell hemoglobin, HbS, it is a ____________ residue.
Ans:  valine     Section:  7.4


19. As the partial pressure of carbon dioxide increases, the affinity of oxygen binding to hemoglobin ______________.
Ans:  decreases     Section:  7.3


20. 2,3-Bisphosphoglycerate binds only to the __________________ form of hemoglobin.
Ans:  T-, or deoxy     Section:  7.2



Multiple-Choice Questions


21. What factor(s) influence(s) the binding of oxygen to myoglobin?
A) The concentration of bicarbonate ion, HCO3
B) The partial pressure of oxygen, pO2
C) The concentration of hemoglobin present
D) The concentration of 2,3-BPG
E) Both b and d
Ans:  B     Section:  7.2


22. Which of the following is correct concerning the differences between hemoglobin and myoglobin?
A) Both hemoglobin and myoglobin are tetrameric proteins.
B) Hemoglobin exhibits a hyperbolic O2 saturation curve while myoglobin exhibits a sigmoid shaped curve.
C) Hemoglobin exhibits cooperative binding of O2 while myoglobin does not.
D) Hemoglobin exhibits a higher degree of O2 saturation at all physiologically relevant partial pressures of O2 than does myoglobin.
E) All of the above.
Ans:  C     Section:  7.2


23. Which of the following is not correct concerning myoglobin?
A) The globin chain contains an extensive α-helix structure.
B) The heme group is bound to the globin chain by two disulfide bonds to cysteine residues.
C) The iron of the heme group is in the Fe+2 oxidation state.
D) The diameter of the iron ion decreases upon binding to oxygen.
E) The function of myoglobin is oxygen storage in muscle.
Ans:  B     Section:  7.1


24. The structure of normal adult hemoglobin can be described as
A) a tetramer composed of four myoglobin molecules.
B) a tetramer composed of two αβ dimers.
C) a tetramer composed of two α2 and two β2 dimers.
D) a tetramer composed of two α2 and two γ2 dimers.
E) None of these accurately describe hemoglobin.
Ans:  B     Section:  7.1


25. Which of the following is correct concerning fetal hemoglobin?
A) Fetal hemoglobin is composed of two α and two γ subunits.
B) Fetal hemoglobin binds 2,3-BPG more tightly than normal adult hemoglobin.
C) Fetal hemoglobin binds oxygen less than HbA at all pO2.
D) Fetal hemoglobin does not exist in the T-form.
E) None of the above.
Ans:  A     Section:  7.2


26. Hemoglobin-binding of oxygen is best described as a
A) concerted model.
B) Michaelis-Menten model.
C) sequential model.
D) combination of sequential and concerted models.
E) None of the above.
Ans:  D     Section:  7.2


27. 2-3 Bisphosphoglycerate
A) binds in the central cavity in the T-form of hemoglobin.
B) preferentially binds to deoxyhemoglobin and stabilizes it.
C) is present in the red blood cells.
D) All of the above.
E) None of the above.
Ans:  D     Section:  7.2


28. What is the Bohr effect?
A) the ability of hemoglobin to retain oxygen when in competition with myoglobin
B) the regulation of hemoglobin-binding by hydrogen ions and carbon dioxide
C) the alteration of hemoglobin conformation during low oxygen stress
D) All of the above.
E) None of the above.
Ans:  B     Section:  7.3


29. Why is the HbS mutation so prevalent in Africa and other tropical regions?
A) The oxygen binds with greater affinity to the proximal histidine residue of HbS.
B) Bonding of carbon dioxide to HbS molecules increases the binding of oxygen.
C) Hemoglobin binds more oxygen with the reduction of the hemoglobin S chain.
D) Hemoglobin binds more oxygen with aggregations of α chains found in sickle-cell hemoglobin.
E) People with sickle-cell trait are resistant to malaria, increasing the prevalence of the HbS allele.
Ans:  E     Section:  7.4


30. Which of the following describes the Bohr effect?
A) Lowering the pH results in the release of O2 from oxyhemoglobin.
B) Increasing the pressure of CO2 results in the release of O2 from oxyhemoglobin.
C) Increasing the pH increases the T-form of hemoglobin.
D) All of the above.
E) a and b.
Ans:  E     Section:  7.3


31. Which of the following is correct concerning the following equilibria?

CO2  +  H2O    H2CO3

A) An increase in the pressure of CO2 will result in a decrease of pH.
B) This reaction is catalyzed by carbonic anhydrase.
C) The H2CO3 dissociates to H+ and bicarbonate ion, HCO3.
D) The majority of CO2 is transported to the lungs in the form of HCO3.
E) All of the above.
Ans:  E     Section:  7.3


32. Carbon dioxide forms carbamate groups in proteins by reaction with
A) aspartate residues.
B) cysteine residues.
C) N-terminal amino groups.
D) tyrosine residues.
E) heme groups.
Ans:  C     Section:  7.3


33. Sickle-cell anemia is caused by
A) a decreased production of α chains of hemoglobin.
B) a substitution of a Glu residue for a Phe residue at the β6 position.
C) the loss of the heme group because the proximal His is oxidized.
D) a substitution of a Val residue for a Glu residue at the β6 position.
E) a substitution of Glu residue for His at the C-terminal of the α chain.
Ans:  D     Section:  7.4



34. Which of the following is correct concerning the oxygenation plot of proteins X and Y shown below?
A) Protein Y exhibits tighter oxygen-binding than protein X.
B) Protein Y corresponds to fetal hemoglobin, and protein X corresponds to normal adult hemoglobin.
C) Protein X corresponds to fetal hemoglobin, and protein Y corresponds to normal adult hemoglobin.
D) Protein X corresponds to myoglobin, and protein Y corresponds to hemoglobin.
E) None of the above.
Ans:  C     Section:  7.2


35. Which of the following is not correct concerning the oxygenation plot of proteins X and Y shown below?
A) Protein X exhibits tighter oxygen binding than protein Y.
B) Protein Y would function as a better transport protein than protein X.
C) Protein X exhibits cooperative binding, whereas Y does not.
D) Protein X corresponds to myoglobin, and protein Y corresponds to hemoglobin.
E) Protein Y contains multiple binding sites.
Ans:  C     Section:  7.2


36. Which is not correct concerning the models that are accepted to describe cooperative binding?
A) In the sequential model, the binding of a ligand changes the conformation of the subunit to which it binds, which in turn induces a change in neighboring subunits.
B) All known allosteric proteins exhibit either the concerted or sequential model exclusive of the other.
C) Both models incorporate a low affinity T-state and a higher affinity R-state.
D) Both models explain the sigmoid-shaped binding curve.
E) In the concerted model, all molecules exist either in the T-state or the R-state.
Ans:  B     Section:  7.2


37. Consider the oxygen-binding profile at three different pH values of 7.6, 7.4, and 7.2.  Which statement is most correct?


A) Curve X most likely corresponds to pH 7.2.
B) Curve Z most likely corresponds to pH 7.6.
C) Hb has a higher affinity for oxygen at the pH of curve Z.
D) Curve Y most likely corresponds to pH 7.4.
E) pH has no effect on the oxygenation of hemoglobin.
Ans:  D     Section:  7.3


38. What would be the expected result of a Lys residue being substituted with a Ser residue in the BPG binding site of hemoglobin?
A) BPG would bind tighter because of the loss of a positive charge.
B) BPG would bind tighter because of the gain of a positive charge.
C) BPG would bind less tightly because of the loss of a positive charge
D) BPG would bind less tightly because of the gain of a positive charge.
E) This substitution would have no effect on the binding of BPG.
Ans:  C     Section:  7.2



Short-Answer Questions


39. Why is it advantageous for hemoglobin to have allosteric properties?
Ans: Hemoglobin binds oxygen in a positive cooperative manner. This allows it to become saturated in the lungs, where oxygen pressure is high. When the hemoglobin moves to tissues, the lower oxygen pressure induces it to release oxygen and thus deliver oxygen where it is needed.
Section:  7.2


40. What is fetal hemoglobin? How does it differ from adult hemoglobin?
Ans: Fetal hemoglobin contains two a and two g chains, in contrast to adult hemoglobin with two a and two b chains. The fetal hemoglobin g chain is probably a result of gene duplication and divergence. The difference in the chains results in a lower binding affinity of 2-3 BPG to fetal hemoglobin. Thus, the fetal hemoglobin has a higher affinity for oxygen, and the oxygen is effectively transferred from the mother’s hemoglobin to fetal hemoglobin.
Section:  7.2


41. What is metmyoglobin?
Ans: Metmyoglobin is formed when the heme iron ion, which is normally in the +2 oxidation state, is oxidized to the +3 oxidation state.  This oxidized form of myoglobin does not bind molecular oxygen and is not functional.
Section:  7.1


42. Describe the recurring structure called the globin fold.
Ans: Each of the four subunits of hemoglobin consists of a set of α helices in the same arrangement as the α helices of myoglobin. The arrangement is known as the globin fold.
Section:  7.1


43. What functional role does the “distal histidine” play in the function of myoglobin and hemoglobin?
Ans: The bonding between the iron and oxygen can be described as a combination of resonance structures, one with Fe2+ and dioxygen and another with Fe3+ and superoxide.  The “distal histidine” donates a hydrogen bond to this complex, stabilizing the complex, and inhibits the oxidation of the iron to the ferric state.
Section:  7.1


44. Draw the oxygen-binding curve of myoglobin and that of hemoglobin.  Indicate the partial pressure of oxygen in the lungs and the range of pressure in tissue.




20 – 40 torr



Section:  7.2 and Figure 7.8


45. Describe the structure of normal adult hemoglobin.
Ans: Normal adult hemoglobin, HbA, is a tetramer.  It is composed of two α subunits and two β subunits.  Each subunit has a structure very similar to myoglobin.  It can be best described as a pair of identical αβ dimers.  Each subunit contains a heme group.  So, each molecule of hemoglobin can bind up to four molecules of oxygen.
Section:  7.2


46. What is neuroglobin and what is its suspected role?
Ans: Neuroglobin is expressed in the brain, and at especially high levels in the retina. It may play a role in protecting neural tissues from hypoxia.
Section:  7.4


47. Describe the concerted model to explain allosteric cooperative binding.
Ans: The protein exists in two conformations: a T-state (for tense) that has a lower affinity for the ligand and an R-state (for relaxed) that has a higher affinity for the ligand.  In the concerted model, all of the molecules exist either in the T-state or in the R-state.  At each ligand concentration, there is an equilibrium between the two states.  An increase in the ligand concentration shifts the equilibrium from the T- to the R-state.
Section:  7.2


48. Describe the role of 2,3-bisphosphoglycerate in the function of hemoglobin.
Ans: 2,3-bisphosphoglycerate, 2,3-BPG, is a relatively small, highly anionic molecule found in the RBC.  2,3-BPG only binds to the center cavity of deoxyhemoglobin (T-state).  The size of the center cavity decreases upon the change to the R-form so that it cannot bind to the R-state.  Thus, the presence of 2,3-BPG shifts the equilibrium toward the T-state. The  T-state is unstable, and without BPG, the equilibrium shifts so far toward the R-state that little oxygen would be released under physiological conditions.
Section:  7.2


49. Describe the chemical basis of the Bohr effect.
Ans: The effect observed by Christian Bohr is that hemoglobin becomes deoxygenated as the pH decreases.  In deoxyhemoglobin, three amino acid residues form two salt bridges that stabilize the T-state.  One of these is formed between the C-terminal His β146 and an Asp residue (β94).  As the pH increases, this stabilizing salt bridge is broken because His becomes deprotonated and loses its positive charge.  At lower pH values, this His is positively charged.  The formation of the salt bridge shifts the equilibrium from the R-state to the T-state, thus releasing oxygen.
Section:  7.3


50. Describe how carbon dioxide affects the oxygenation of hemoglobin.
Ans: Increased levels of carbon dioxide cause hemoglobin to release oxygen.  The more active the tissue, the more fuel is burned and the more CO2 is produced.  These active tissue cells have the greatest need for oxygen to produce more energy.  The CO2 combines with the N-terminal amino groups to form negatively charged carbamate groups.  The negatively charged carbamate groups form salt bridges that stabilize the T-state.  Thus, the increase of carbon dioxide causes the conversion of the R-state to the T-state, releasing the bound oxygen to the tissues producing the most CO2.
Section:  7.3


51. Briefly describe the cause of sickle-cell anemia.
Ans: Sickle-cell anemia is a genetic disorder that is the result of a single substitution of β6 Glu with a Val.  This changes a negatively charged side chain to a nonpolar, hydrophobic side chain.  This Val binds into a hydrophobic pocket on the β chain of an adjacent molecule whose β6 Val binds to another molecule, thus hemoglobin aggregates.  These aggregates form long fibers that strain the RBC and force into a sickled shape.  The distorted red blood cells clog capillaries and impair blood flow, resulting in the sickle-cell crisis.  The sickled cells are then destroyed, resulting in the anemia.
Section:  7.4


52. What is thalassemia?
Ans: Thalassemia is caused by the substantial decreased production of one of the subunits of hemoglobin.  In α-thalassemia, the decreased production of the α chain results in the formation of tetramers of only the β chain.  This β4 binds oxygen more tightly than HbA and does not exhibit cooperative binding.  In β-thalassemia, the α chains form insoluble aggregates in the immature red blood cells.
Section:  7.4


53. What is the role of α-hemoglobin stabilizing protein?
Ans: Four genes express the α chains, and only two genes express the β chain.  Thus, there is an excess of α chains, which if allowed, would aggregate and become insoluble.  Red blood cells produce α-hemoglobin stabilizing protein (AHSP), which binds to the α chain monomers to from a soluble complex.  This prevents the aggregation of the α subunits.
Section:  7.4

Chapter 27   The Integration of Metabolism



Matching Questions

Use the following to answer Questions 1–10:


Choose the correct answer from the list below. Not all of the answers will be used.

  1. a) brain
  2. b) leptin
  3. c) cholecystokinin
  4. d) fatty acids
  5. e) glucose
  6. f) glycerol
  7. g) muscle
  8. h) alanine
  9. i) ketone bodies
  10. j) leucine
  11. k) glucagon
  12. l) liver


1. ____________ This hormone is released by cells of the small intestine and generates a sense of satiation and inhibits the appetite.


Ans:  c
Section:  27.2


2. ____________ Glucose is virtually the sole energy source for this organ.


Ans:  a
Section:  27.5


3. ____________ Most of the body’s glycogen is stored this organ.


Ans:  g
Section:  27.5


4. ____________ This molecule is needed by adipose tissue to synthesize triacylglycerols.


Ans:  e
Section:  27.5


5. ____________ After a day of starvation, the muscles rely exclusively on this fuel.


Ans:  d
Section:  27.5


6. ____________ This organ is considered to be the metabolic “hub” of the body.


Ans:  l
Section:  27.2


7. ____________ After days or weeks of starvation, this becomes the major metabolic fuel of the brain.


Ans:  i
Section:  27.5


8. ____________ This hormone is released by adipose tissue and generates a sense of satiation and inhibits the appetite.


Ans:  b
Section:  27.2


9. ____________ This metabolite is produced by the adipose cells but can only be metabolized in the liver.


Ans:  f
Section:  27.5


10. ____________ This hormone stimulates glycogen breakdown and gluconeogenesis.


Ans:  k
Section:     Introduction



Fill-in-the-Blank Questions


11. Glycolysis and gluconeogenesis are usually _________________ regulated.
Ans:  reciprocally     Section:  Introduction


12. When levels of ketone bodies are high, the _________________ can no longer maintain acid-base balance in the blood
Ans:  kidney     Section:  27.3


13. ____________________ results when insulin is absent due to autoimmune destruction of the β cells of the pancreas.
Ans:  Type 1 diabetes     Section:  27.3


14. When running a marathon, fuel sources from ___________________, muscle, and adipose are used.
Ans:  the liver     Section:  27.4


15. Obesity is defined as a BMI of greater than________________________.
Ans:  30 kg m-2      Section:  27.1


16. The “fed state” leads to the release of the hormone ____________________.
Ans:  insulin     Section:  27.5


17. The primary target organ of glucagon is the ___________________.
Ans:  liver     Section:  27.5


18. ATP production from ___________________ is essential for long-distance running.
Ans:  fatty acids     Section: 27.4


19. The dehydrogenase metabolism of ethanol leads to an excess production of ________________.
Ans:  NADH     Section:  27.6


20. The microsomal ethanol-oxidizing system (MEOS) consumes ______________, which leads to oxidative stress.
Ans:  NADPH     Section:  27.6



Multiple-Choice Questions


21. Excess alcohol consumption can lead to Wernicke-Korsaff syndrome due to the lack of the vitamin thiamine.  Which of the following metabolic conversions cannot occur in the absence of thiamine?
A) Pyruvate  + CO®  oxaloacetate
B) Pyruvate  ®  acetyl-CoA + CO2
C) a-ketoglutarate  ®  succinyl-CoA +  CO2
D) Phosphoenolpyruvate  +  CO®  oxaloacetate
E) B and C
Ans:  E     Section:  27.6


22. All of the following occur in the pancreatic β cell when blood glucose levels increase.
A) Insulin is secreted by receptor-mediated endocytosis.

B) Intracellular ATP/ADP levels increase.

C) K+ channels close, altering the membrane potential.

D) A Ca2+ channel opens.

E) All of the above.

Ans:  A     Section:  27.2


23. The key regulatory enzyme in glycolysis is
A) phosphofructokinase. D) triose phosphate isomerase.
B) glucokinase. E) None of the above.
C) hexokinase.
Ans:  A     Section:  27.3


24. The function(s) of aerobic glycolysis include(s)
A) degrading glucose to provide ATP.
B) providing carbon skeletons for biosynthesis.
C) providing NADH for lactate reduction.
D) A and B.
E) A, B, and C.
Ans:  D     Section:  27.4


25. What are the fuels used in a long distance run?
A) Creatine phosphate
B) Anaerobic glycolysis
C) Muscle glycogen
D) A and B
E) A, B, and C
Ans:  C     Section:  27.4


26. The Second Law of Thermodynamics translated into dietary terms can be stated as
A) energy expended = energy consumed + energy stored. D) kinetic energy = Energy consumed + energy stored.
B) potential energy = energy consumed + energy expended. E) None of these really state the Second Law of Thermodynamics.
C) energy consumed = energy expended + energy stored.
Ans:  C     Section:  27.1


27. Health consequences of obesity include
A) coronary heart disease. D) sleep apnea.
B) hpertension. E) abnormal menses.
C) stroke. F) All of the above.
Ans:  F     Section:  27.1


28. GLP-1 triggers which of the following in the brain?
A) Decreased satiety D) All of the above
B) Decreased food intake E) B and C
C) Decreased body weight
Ans:  E     Section:  27.2


29. Which of the following is the fuel used by the brain during starvation?
A) Ketone bodies D) Branched chain amino acids
B) Glycogen E) Fatty acids
C) Amino acids
Ans:  A     Section:  27.5


30. In a typical human male, what is the energy content (in kcal) of triacylglycerols stored in adipose tissue?
A) 13,500 kcal D) 13,500 cal
B) 135,000 kcal E) None of the above
C) 1,350,000 kcal
Ans:  B     Section:  27.5


31. The ___________ is an important source of metabolites for gluconeogenesis during starvation.
A) kidney     B) brain     C) intestine     D) muscle     E) red blood cells
Ans:  D     Section:  27.5


32. What is the primary source of energy used by the muscle during starvation?
A) Glucose D) Ketone bodies
B) Lactate E) Branched chain amino acids
C) Fatty acids
Ans: C     Section:  27.5


33. Maintenance of a constant blood-glucose level is called
A) glucose tolerance. D) cholecystokinin.
B) glucose adjustment. E) None of the above.
C) glucose homeostasis.
Ans:  C     Section:  27.4


34. Insulin signals the ______ state, and glucagon signals the _______ state.
A) fed; starved D) maintenance; fed
B) starved; fed E) starved; maintenance
C) fed; maintenance
Ans:  A     Section:  27.4


35. Which of the following molecules or metabolic conversions provides the maximum rate of ATP production (mmol/sec) for muscle contraction?
A) Conversion of muscle glycogen to CO2
B) Conversion of muscle glycogen to lactate
C) Creatine phosphate
D) Conversion of fatty acid to CO2
E) Conversion of liver glycogen to CO2
Ans:  C     Section:  27.4



Short-Answer Questions


36. What are the two factors that have led to a propensity to gain weight in humans and how they can be negated?
Ans: Evolutionarily, our bodies are programmed to rapidly store fat in times of plenty in case there is not enough tomorrow. The second factor is that we are no long susceptible to predation and can survive a more sedentary life style.  Weight gain can be negated behaviorally, that is, by eating less and exercising more.
Section:  27.1


37. What are the two signals from the gastrointestinal tract that induce feelings of satiety?
Ans: CCK is secreted into the blood by cells in the duodenum and jejunum and binds to receptors in the peripheral nervous system. The signal is relayed to the brain and generates a feeling of satiety. GLP-1 is secreted by intestinal L cells and acts through a G-protein-coupled receptor to induce feelings that inhibit further eating.
Section:  27.1


38. What are the sources of glucose 6-phosphate in liver cells?
Ans: Glucose 6-phosphate is produced from free glucose after it enters the cell.  Two other common sources of glucose 6-phosphate are from the breakdown of glycogen and from gluconeogenesis.
Section:  27.5


39. Show how the metabolism of the liver with skeletal muscle is interconnected by blood glucose and alanine during strenuous exercise.
Ans: See Figures 27.1 and 27.6.


Section:  27.3


40. What is the advantage of converting pyruvate to lactate in skeletal muscle?
Ans: One advantage is that NAD+ is regenerated, so energy can continue to be extracted from glucose during strenuous exercise. The conversion buys the system time and shifts the metabolic burden to other tissues during stress.
Section:  27.4


41. What are some of the primary metabolic fates of acetyl CoA?
Ans: Acetyl CoA can enter the citric acid cycle where it is oxidized to carbon dioxide.  It can also be exported as citrate to the cytosol where it can be converted into fatty acids. It can be used in the synthesis of molecules such as 3-hydroxy-3-methylglutaryl CoA, which are precursors of the steroids.
Section:  27.1


42. What are the plasma concentrations of glucose in the normal fasting and starvation states?
Ans: Typical fasting glucose level in the plasma is 4.7 mM (~85 mg dl-1), and the typical glucose concentration during starvation is 2.2 mM (~40 mg dl-1).
Section:  27.5 and Figure 27.12


43. What is the major fuel for resting muscle and what it the major fuel for muscle under strenuous work conditions?
Ans: Fatty acids are the major fuel for resting muscle cells.  Glucose is the major fuel under strenuous exercise.
Section:  27.4


44. How do SOCS (suppressors of cytokine signaling) proteins inhibit receptor signaling?
Ans: SOCS proteins bind to phosphorylated tyrosine residues on receptors disrupting signal flow. Also, the binding of SOCS proteins to components of the signal-transduction pathway may enhance proteasome degradation of these components.  SOCS deleted in POMC-expressing neurons of mice display an enhanced sensitivity to leptin, and the mice are resistant to weight gain.
Section:  27.2


45. What are the two hypotheses supporting low-carbohydrate-high-protein diets as an effective weight losing strategy?
Ans: First, proteins seem to induce a feeling of satiation more effectively than do fats or carbohydrates. Second, proteins require more energy to digest than do fats or carbohydrates.
Section:  27.2


46. Describe how low glucose levels can decrease triacylglycerol synthesis in adipose tissue.
Ans: Triacylglycerols are produced from fatty acyl-CoA and glycerol 3-phosphate.  The glycerol 3-phosphate is produced by the reduction of dihydroxyacetone phosphate, a glycolytic intermediate.  Adipose tissue does not have glycerol kinase to form the glycerol 3-phosphate from free glycerol.  It must come from glucose.
Section:  27.4


47. Explain what is meant by the term the starved-fed cycle? What are the stages?
Ans: A starved-fed cycle is experienced in the hours after the evening meal, through night’s fast, culminating with breakfast the next morning.  There are three stages: postabsorptive after the evening meal, early fasting during the night, and the refed state after breakfast.
Section: 27.5


48. What metabolic changes occur during the early fasting state?
Ans: In the initial hours after a meal, the blood-glucose levels start to decrease, the insulin decreases, and glucagon is secreted by the α-cells of the pancreas. Glucagon stimulates the liver to mobilize glycogen stores, blocks glycogen synthesis, and inhibits fatty acid synthesis.  Glucagon also stimulates gluconeogenesis and blocks glycolysis.  These processes make glucose available to the other tissues of the body.
Section:  27.5


49. What is the cause of Type 1 diabetes?
Ans: This form appears to be caused by autoimmune response. The insulin-secreting cells in the pancreas are damaged and cannot properly supply insulin.
Section:  27.3


50. Describe the stages of ethanol consumption that affect liver damage and lead to death.
Ans: There are three stages. First, a fatty-liver state is formed due to the increased levels of NADH that inhibit fatty-acid oxidation and stimulate fatty-acid synthesis. In the next stage, alcoholic hepatitis begins due to oxidative damage, cells die, and inflammation begins. In the final stage, cirrhosis, fibrous tissues, and scars impair biochemical function. Ammonia cannot be converted to urea, and its toxicity leads to coma and death.
Section:  27.6