Chapter 5 Protein Function
Multiple Choice Questions
1. Reversible binding of a protein to a ligand: oxygen-binding proteins
The interactions of ligands with proteins:
A) are relatively nonspecific.
B) are relatively rare in biological systems.
C) are usually irreversible.
D) are usually transient.
E) usually result in the inactivation of the proteins.
2. Reversible binding of a protein to a ligand: oxygen-binding proteins
A prosthetic group of a protein is a non-protein structure that is:
A) a ligand of the protein.
B) a part of the secondary structure of the protein.
C) a substrate of the protein.
D) permanently associated with the protein.
E) transiently bound to the protein.
3. Reversible binding of a protein to a ligand: oxygen-binding proteins
When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are
occupied by:
A) one O atom and one amino acid atom.
B) one O2 molecule and one amino acid atom.
C) one O2 molecule and one heme atom.
D) two O atoms.
E) two O2 molecules.
4. Reversible binding of a protein to a ligand: oxygen-binding proteins
In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the
fraction of binding sites occupied can best be described as:
A) hyperbolic.
B) linear with a negative slope.
C) linear with a positive slope.
D) random.
E) sigmoidal.
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5. Reversible binding of a protein to a ligand: oxygen-binding proteins
Which of the following statements about protein-ligand binding is correct?
A) The Ka is equal to the concentration of ligand when all of the binding sites are occupied.
B) The Ka is independent of such conditions as salt concentration and pH.
C) The larger the Ka (association constant), the weaker the affinity.
D) The larger the Ka, the faster is the binding.
E) The larger the Ka, the smaller the Kd (dissociation constant).
6. Reversible binding of a protein to a ligand: oxygen-binding proteins
Myoglobin and the subunits of hemoglobin have:
A) no obvious structural relationship.
B) very different primary and tertiary structures.
C) very similar primary and tertiary structures.
D) very similar primary structures, but different tertiary structures.
E) very similar tertiary structures, but different primary structures.
7. Reversible binding of a protein to a ligand: oxygen-binding proteins
An allosteric interaction between a ligand and a protein is one in which:
A) binding of a molecule to a binding site affects binding of additional molecules to the same site.
B) binding of a molecule to a binding site affects binding properties of another site on the protein.
C) binding of the ligand to the protein is covalent.
D) multiple molecules of the same ligand can bind to the same binding site.
E) two different ligands can bind to the same binding site.
8. Reversible binding of a protein to a ligand: oxygen-binding proteins
In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by:
A) Fe2+ binding.
B) heme binding.
C) oxygen binding.
D) subunit association.
E) subunit dissociation.
9. Reversible binding of a protein to a ligand: oxygen-binding proteins
Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?
A) It binds at a distance from the heme groups of hemoglobin.
B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.
C) It increases the affinity of hemoglobin for oxygen.
D) It is an allosteric modulator.
E) It is normally found associated with the hemoglobin extracted from red blood cells.
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10. Reversible binding of a protein to a ligand: oxygen-binding proteins
Which of the following is not correct concerning cooperative binding of a ligand to a protein?
A) It is usually a form of allosteric interaction.
B) It is usually associated with proteins with multiple subunits.
C) It rarely occurs in enzymes.
D) It results in a nonlinear Hill Plot.
E) It results in a sigmoidal binding curve.
11. Reversible binding of a protein to a ligand: oxygen-binding proteins
Carbon monoxide (CO) is toxic to humans because:
A) it binds to myoglobin and causes it to denature.
B) it is rapidly converted to toxic CO2.
C) it binds to the globin portion of hemoglobin and prevents the binding of O2.
D) it binds to the Fe in hemoglobin and prevents the binding of O2.
E) it binds to the heme portion of hemoglobin and causes heme to unbind from hemoglobin.
12. Reversible binding of a protein to a ligand: oxygen-binding proteins
The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein
because of ___________ interactions between molecules.
A) covalent
B) disulfide
C) hydrogen bonding
D) hydrophobic
E) ionic
13. Reversible binding of a protein to a ligand: oxygen-binding proteins
The fundamental cause of sickle-cell disease is a change in the structure of:
A) blood.
B) capillaries.
C) hemoglobin.
D) red cells.
E) the heart.
14. Reversible binding of a protein to a ligand: oxygen-binding proteins
Neuroglobin is a member of the globin family found in neurons. It is a monomeric protein that helps
protect the brain from hypoxia (low O2). Identify the correct statement(s) about neuroglobin below.
a) It binds O2 with a hyperbolic binding curve.
b) It binds O2 with a sigmoidal binding curve.
c) It binds O2 with higher affinity than hemoglobin.
d) It binds O2 with lower affinity than hemoglobin.
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A) a and c
B) a and d
C) b and c
D) b and d
E) None of the above
15. Reversible binding of a protein to a ligand: oxygen-binding proteins
Patients with chronic hypoxia (low O2 levels) due to decreased lung function may adapt by increasing their
circulating BPG levels. Predict which of the following will be true for such a patient.
A) p50 for O2 will be decreased.
B) p50 for O2 will be increased.
C) The R-state of hemoglobin will be favored.
D) O2 binding to hemoglobin will be hyperbolic.
E) None of the above
16. Reversible binding of a protein to a ligand: oxygen-binding proteins
Identify the correct statements regarding the Bohr effect in hemoglobin.
a) The Bohr effect shifts the fractional O2 saturation curve to the right as pH decreases.
b) The Bohr effect shifts the fractional O2 saturation curve to the right as the pH increases.
c) The Bohr effect favors O2 release in respiring tissues.
d) O2 and H+ compete for binding to Hb.
A) a and c
B) a and d
C) b and c
D) b and d
E) b, c, and d
17. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
An individual molecular structure within an antigen to which an individual antibody binds is as a(n):
A) antigen.
B) epitope.
C) Fab region.
D) Fc region
E) MHC site.
18. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Which of the following parts of the IgG molecule are not involved in binding to an antigen?
A) Fab
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B) Fc
C) Heavy chain
D) Light chain
E) Variable domain
19. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies:
A) are labeled with chemicals that can be visualized.
B) are produced by cells from the same organism that produced the antigen.
C) are synthesized by a population of identical, or “cloned,” cells.
D) are synthesized only in living organisms.
E) have only a single polypeptide chain that can recognize an antigen.
20. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
Which of the following generalizations concerning motor proteins is correct?
A) They convert chemical energy into kinetic energy.
B) They convert chemical energy into potential energy.
C) They convert kinetic energy into chemical energy.
D) They convert kinetic energy into rotational energy.
E) They convert potential energy into chemical energy.
21. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
The predominant structural feature in myosin molecules is:
A) a structure.
B) an helix.
C) the Fab domain.
D) the light chain.
E) the meromyosin domain.
22. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
The energy that is released by the hydrolysis of ATP by actin is used for:
A) actin filament assembly.
B) actin filament disassembly.
C) actin-myosin assembly.
D) actin-myosin disassembly.
E) muscle contraction.
23. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
During muscle contraction, hydrolysis of ATP results in a change in the:
A) conformation of actin.
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B) conformation of myosin.
C) structure of the myofibrils.
D) structure of the sarcoplasmic reticulum.
E) structure of the Z disk.
Short Answer Questions
24. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 153 Difficulty: 1
Describe the concept of “induced fit” in ligand-protein binding.
25. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 154 Difficulty: 2
Explain why most multicellular organisms use an iron-containing protein for oxygen binding rather
than free Fe2+. Your answer should include an explanation of (a) the role of heme and (b) the role of
the protein itself.
26. Reversible binding of a protein to a ligand: oxygen-binding proteins
Pages: 155−157 Difficulty: 2
Describe how you would determine the Ka (association constant) for a ligand and a protein.
27. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 163−164 Difficulty: 1
Why is carbon monoxide (CO) toxic to aerobic organisms?
28. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 156 Difficulty: 2
For the binding of a ligand to a protein, what is the relationship between the Ka (association constant),
the Kd (dissociation constant), and the affinity of the protein for the ligand?
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29. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 156 Difficulty: 2
What fraction of ligand binding sites are occupied () when [ligand] = Kd? Show your work.
30. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 158 Difficulty: 2
Explain briefly why the relative affinity of heme for oxygen and carbon monoxide is changed by the
presence of the myoglobin protein.
31. Reversible binding of a protein to a ligand: oxygen-binding proteins
Pages: 156, 161 Difficulty: 3
Explain why the structure of myoglobin makes it function well as an oxygen-storage protein, whereas
the structure of hemoglobin makes it function well as an oxygen-transport protein.
Pages: 162−165 Difficulty: 2
Describe briefly the two principal models for the cooperative binding of ligands to proteins with
multiple binding sites.
33. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 167 Difficulty: 2
How does BPG binding to hemoglobin decrease its affinity for oxygen?
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34. Reversible binding of a protein to a ligand: oxygen-binding proteins
Page: 166 Difficulty: 2
(a) What is the effect of pH on the binding of oxygen to hemoglobin (the Bohr Effect)? (b) Briefly
describe the mechanism of this effect.
35. Reversible binding of a protein to a ligand: oxygen-binding proteins
Pages: 168−169 Difficulty: 2
Explain how the effects of sickle cell disease demonstrate that hemoblobin undergoes a
conformational change upon releasing oxygen.
36. Reversible binding of a protein to a ligand: oxygen-binding proteins
37. Pages: 171-172 Difficulty: 2
Fetal hemoglobin binds BPG with lower affinity than adult hemoglobin. How does this property
facilitate tranfers of O2 from mother to fetus?
38. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Page: 170 Difficulty: 1
Why is it likely that the immune system can produce a specific antibody that can recognize and bind
to any specific chemical structure?
39. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Page: 171 Difficulty: 2
Describe briefly the basic structure of an IgG protein molecule.
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40. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Page: 173 Difficulty: 2
What is the chemical basis for the specificity of binding of an immunoglobin antibody to a particular
antigen?
41. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Page: 173 Difficulty: 2
What is the concept of “induced fit” as it applies to antigen-antibody binding?
42. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Page: 173 Difficulty: 2
Describe how immunoaffinity chromatography is performed.
43. Complementary interactions between proteins and ligands: the immune system and
immunoglobulins
Pages: 173−175 Difficulty: 2
What properties of antibodies make them useful biochemical reagents? Describe one biochemical
application of antibodies (with more than just the name of the technique).
44. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
Page: 175 Difficulty: 2
Describe briefly the structure of myosin.
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45. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
Page: 176 Difficulty: 1
What is the relationship between G-actin and F-actin?
46. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
Page: 178 Difficulty: 2
What is the role of ATP and ATP hydrolysis in the cycle of actin-myosin association and
disassociation that leads to muscle contraction?
47. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
Page: 178 Difficulty: 2
Describe the cycle of actin-myosin association and disassociation that leads to muscle contraction.
48. Protein interactions modulated by chemical energy: actin, myosin, and molecular motors
Pages: 177−179 Difficulty: 2
Although the myosin molecule “walks” along actin in discrete steps, you are able to make smooth
motions using your muscles. Explain how this is possible.