Chapter 7 - Protein Function Myoglobin and Hemoglobin, Muscle Contraction, and Antibodies Practice Quiz PDF

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This is the chapter 7 assignment of biochem I. Contains questions and answers. ...

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1/15 Biochemistry I Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contraction, and Antibodies Textbook: Fundamentals of Biochemistry: Life at the Molecular Level, 5th Edition. Donald Voet; Judith G. Voet Practice Quiz (WileyPLUS) 1. In myoglobin, the amino acid His F8 is the only ligand for the heme that is supplied by the protein. 2. The secondary structure of myoglobin consists of eight α-helices and the connecting loops. 3. True or false. Myoglobin increases the effective solubility of oxygen in muscle cells. True. 4. True or false. p50, or oxygen tension, is the oxygen pressure (pO2) at which hemoglobin or myoglobin is 50% saturated with oxygen. True. 5. What is the fractional saturation of myoglobin at pO2 = 2.8 torr, if p50= 2.8 torr? A. 1.00 B. 0.28 C. 2.80 D. 0.50 NOTE: Y = pO2 / (p50 + pO2) = 2.8 / (2.8 + 2.8) = 0.5 6. Shown below are statements matching scientists with their accomplishments. Which of the statements below is INCORRECT: A. Max Perutz: In 1968 he reported the structure of hemoglobin at near atomic resolution. B. Archibald Hill: In 1910 he analyzed the sigmoidal oxygen dissociation curve of hemoglobin. C. John Kendrew: A colleague of Perutz who was also awarded the 1962 Nobel Prize in Chemistry.

2/15 D. J. D. Bernal: Placed a crystal of the protein pepsin in an electron beam and obtained a diffraction pattern along with Dorothy Crowfoot Hodgkin. NOTE: J. D. Bernal: Placed a crystal of the protein pepsin in an X-ray beam and obtained a diffraction pattern along with Dorothy Crowfoot Hodgkin. 7. Which of the following represents the true protomer of hemoglobin? A. α B. α β C. β D. {α}2 β2 8. Shown below are statements matching scientists with their accomplishments. Which of the statements below is INCORRECT: A. Daniel Koshland: Proposed the sequential model of allosterism. B. Christian Bohr: In 1904 he reported the release of protons upon oxygen binding by hemoglobin. C. Max Perutz: In 1945 hypothesized and in 1949 proved that sickle-cell anemia was the result of a mutant hemoglobin that had a less negative ionic charge than normal adult hemoglobin. This was the first evidence that a disease could result from an alteration in the molecular structure of a protein. NOTE: Linus Pauling did this. D. Joseph Barcroft: In 1921 he anticipated the existence of BPG as a factor that decreased the oxygen affinity of hemoglobin. E. Jacques Monod: Formulated the symmetry model of allosterism along with Jeffries Wyman and Jean-Pierre Changeux.

3/15 9. Which of the following is not a rule of the symmetry model of allosterism? A. Each oligomer can exist in two conformational states, designated R and T; these states are in equilibrium. B. The molecular symmetry of the protein is conserved during the conformational change. C. An allosteric protein is an oligomer of symmetrically related subunits. D. Conformational changes occur sequentially as more ligand-binding sites are occupied. 10. Which of the following diseases is not caused by a mutation in hemoglobin? A. Hemophilia B. Sickle-cell anemia C. Polycythemia D. Hemolytic anemia 11. Which of the statements below about hemoglobin is INCORRECT: A. Subunit interfaces in hemoglobin are composed of predominantly salt bridges. NOTE: These interfaces are predominantly hydrophobic. B. Hemoglobin is a tetramer made up of myoglobin-like subunits. C. It has been dubbed an "honorary enzyme" even though it functions in oxygen transport and does not catalyze a chemical reaction. D. Hemoglobin gives red blood cells their color. E. Hemoglobin is part of an oxygen delivery system that is needed for animals that are too large for oxygen to be delivered by simple diffusion. F. The quaternary structure of hemoglobin consists of 4 polypeptide chains.

4/15 12. Which of the statements below about hemoglobin and myoglobin's oxygen binding is INCORRECT: A. In any binding system, a sigmoidal curve is diagnostic of a cooperative interaction between binding sites whereas a hyperbolic binding curve is an indication of a lack of cooperativity. B. The p50 of hemoglobin is nearly 10 times higher than that of myoglobin. C. The Hill coefficient (n) increases with the degree of cooperativity of a reaction: A Hill coefficient of 1 (n = 1) indicates no cooperativity, a Hill coefficient < 1 (n < 1) indicates negative cooperativity and a Hill coefficient > 1 (n > 1) indicates positive cooperativity. D. The reason hemoglobin has a sigmoidal or S-shaped oxygen binding curve whereas myoglobin has a hyperbolic oxygen binding curve is because hemoglobin is a tetramer whereas myoglobin is a monomer. E. Hemoglobin has a Hill coefficient > 1 whereas myoglobin has a Hill coefficient < 1. NOTE: Myoglobin exhibits no cooperativity and so has a Hill coefficient of 1 (n = 1). F. Myoglobin has a higher affinity for oxygen than hemoglobin. 13. Which of the statements below about hemoglobin's oxygen binding is INCORRECT: A. The cooperative binding of O2 by hemoglobin is an example of an allosteric effect (Greek: allos, other stereos, solid or space). Allosteric effects, in which the binding of a ligand at one site affects the binding of another ligand at another site, generally require interactions among subunits of oligomeric proteins.

5/15 B. The binding of oxygen to hemoglobin in an example of positive cooperativity: Oxygen binding favors the T --> R transition switching hemoglobin from the low affinity for oxygen T-state to the high affinity for oxygen R-state. C. Oxygen binding causes a change in the quaternary structure of hemoglobin where hemoglobin changes quaternary structure from the T (tense) state that has a low affinity of oxygen to the R (relaxed) state that has a higher affinity of oxygen. D. In any binding system, a sigmoidal ligand binding curve (like hemoglobin's for O2) indicates an allosteric effect where there is cooperative interaction between binding sites and generally indicates that a protein has more than one subunit. E. Hemoglobin's sigmoidal oxygen binding curve is due to the T --> R transition: The sigmoidal curve results because of the switch from a low affinity oxygen binding hyperbolic curve in the T-state to a high affinity oxygen binding hyperbolic curve in the R-state. F. The T --> R transition in hemoglobin subunits explains the difference in the oxygen affinities of oxy- and deoxyhemoglobin. G. The hemoglobin tetramer can bind 4 molecules of oxygen and because of its positive cooperativity, the fourth O2 molecule binds with 4-fold greater affinity than the first. NOTE: In fact, because of the beneficial effects of positive cooperativity, the fourth O2 molecule binds with 100-fold greater affinity than the first. 14. True or false. The R-state represents the conformation of deoxyhemoglobin and the T-state represents the conformation of oxyhemoglobin. False. NOTE: The opposite is true. 15. Which of the following statements about factors relating to the Bohr effect and the effect on CO2 on oxygen transport is NOT true:

6/15 A. Dissolved CO2 is converted to bicarbonate by the enzyme carbonic anhydrase. A proton (H+) is released in the reaction: Thus, the release of CO2 by actively respiring cells causes the release of protons causing hemoglobin to release the oxygen needed by these cells via the Bohr effect. B. Under physiological conditions, hemoglobin releases ~ 0.6 protons for each bound O2. C. The Bohr effect involves the O2 affinity of hemoglobin increasing with increasing pH. Thus increasing the pH stimulates hemoglobin to bind more oxygen. D. CO2 also modulates O2 binding to hemoglobin by allosterically binding the T state but not the R state: Thus when the CO2 concentration is high, as it is in the capillaries, it stabilizes T state, stimulating hemoglobin to release its bound O2. E. The reason for the Bohr effect on the molecular level is because in hemoglobin's Tstate, the formation of ion pairs increases the pK values of certain groups whereas these ion pairings are absent in its R-state and the pK’s of the groups decrease (making them more acidic and more likely to give up protons). F. CO2 modulates O2 binding to hemoglobin by combining reversibly with the Nterminal groups of other blood proteins to form carbonates. The protons released in this reaction promote further O2 release through the Bohr effect. NOTE: The correct statement is: "CO2 modulates O2 binding to hemoglobin by combining reversibly with the N-terminal groups of other blood proteins to form carbamates."

16. Which of the following statments about Sickle Cell anemia is INCORRECT? A. The administration of hydroxyurea is an effective treatment for sickle-cell anemia.

7/15 B. Individuals who are heterozygous carriers of hemoglobin S in an area where malaria is prevalent are more likely to survive to maturity than individuals who are homozygous for normal hemoglobin. C. Hemoglobin S has a lower affinity for oxygen than normal adult hemoglobin (hemoglobin A). NOTE: In fact, their affinities for oxygen are the same. D. The mutation causing sickle cell anemia is that hemoglobin S contains Val rather than Glu at the sixth position of each beta chain. E. Sickle-cell anemia is caused from deoxyhemoglobin S forming insoluble filaments. 17. Which of the following statements about BPG and its effect on oxygen transport is NOT true: A. An initial response in adapting to a higher altitude is increased BPG synthesis in erythrocytes. This increase in BPG causes the O2-binding curve of hemoglobin to shift from its sea-level position to a higher affinity position facilitating better O2 absorption and transport at the elavated altitude. NOTE: The false statement involves the explanation of how BPG helps altitude adaptation. BPG plays a role in high-altitude adaptation. An intial response to moving to a higher altitude is increased BPG synthesis in erythrocytes. This increase in BPG causes the O2-binding curve of hemoglobin to shift from its sea-level position to a lower affinity position - this is actually favorable because it has a steeper slope and delivers more oxygen between the reduced atmospheric pO2 of the elevated altidude and veinous pO2 (see Box 7-3 in the text). B. BPG binds in hemoglobin’s central cavity in the T state but not in the R state. Thus because it binds (and thus stablizes) the T state, BPG has a negative allosteric effect on hemoglobin's binding of oxygen.

8/15 C. The effects of BPG also help supply the fetus with oxygen. A fetus obtains its O2 from the maternal circulation via the placenta. BPG binds more tightly to adult hemoglobin than to fetal hemoglobin thus facilitating the transfer of O2 to the fetus. D. BPG stands for D-2,3 bisphosphoglycerate, shown below:

E. The presence of BPG in mammalian erythrocytes decreases hemoglobin's affinity for oxygen. 18. Which of the following statements about diseases of hemoglobin and the blood is not true: A. Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition. NOTE: Not all hemoglobin variants produce clinical symptoms, but some abnormal hemoglobin molecules do cause debilitating diseases. B. Most of the variant hemoglobins identified result from a single amino acid substitution in a globin polypeptide chain. C. Mutations to that destabilize hemoglobin’s tertiary or quaternary structure, alter its oxygen-binding affinity (p50) and reduce its cooperativity result in diseased states. D. Cyanosis is caused by mutations that favor the oxidation of Fe(II) to Fe(III).

9/15 E. Mutations that increase hemoglobin’s oxygen affinity lead to increased numbers of erythrocytes in order to compensate for the less than normal amount of oxygen released in the tissues - a condition named polycythemia. F. Hemolytic anemia results from the lysis of erythrocytes. G. The bluish skin color associated with cyanosis is due to the presence of methemoglobin in the arterial blood. 19. Shown below is a general diagram of the oxygen binding site as it occurs hemoglobin and myoglobin. Which item in the diagram is incorrectly labeled?

A. B NOTE: B is His E7. The unlabeled His on the bottom is His F8.

10/15 B. D C. A D. C 20. Which of the following statements about blood diseases is not true: A. The bluish skin color associated with cyanosis is due to the presence of methemoglobin in the arterial blood. B. Cyanosis is caused by mutations that favor the oxidation of Fe(II) to Fe(III). C. Mutations that destabilize hemoglobin’s tertiary or quaternary structure, alter its oxygen-binding affinity (p50) and reduce its cooperativity result in diseased states. D. Mutations that increase hemoglobin’s O2 affinity lead to increased numbers of erythrocytes in order to compensate for the less than normal amount of O2 released in the tissues - a condition named polycythemia. E. Hemolytic anemia results from the lysis of erythrocytes. F. Most of the variant hemoglobins identified result from a single amino acid substitution in a globin polypeptide chain. G. Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition. NOTE: Not all hemoglobin variants produce clinical symptoms, but some abnormal hemoglobin molecules do cause debilitating diseases. 21. Select the statement that best matches the following: Myosin A. Functional unit of the myofibril. B. Major component of the thick filament of the myofibril. C. Major component of the thin filament of the myofibril. D. Calcium binding protein.

11/15 E. Chemical energy source for muscle contraction. 22. Select the statement that best matches the following: Actin A. Major component of the thin filament of the myofibril. B. Chemical energy source for muscle contraction. C. Major component of the thick filament of the myofibril. D. Calcium binding protein. E. Functional unit of the myofibril. 23. Select the statement that best matches the following: Troponin C A. Chemical energy source for muscle contraction. B. Major component of the thick filament of the myofibril. C. Functional unit of the myofibril. D. Major component of the thin filament of the myofibril. E. Calcium binding protein. 24. Select the statement the best matches that following: ATP A. Major component of the thick filament of the myofibril. B. Calcium binding protein. C. Chemical energy source for muscle contraction. D. Functional unit of the myofibril. E. Major component of the thin filament of the myofibril. 25. Select the statement that best matches the following: Sarcomere A. Calcium binding protein. B. Major component of the thin filament of the myofibril. C. Major component of the thick filament of the myofibril.

12/15 D. Functional unit of the myofibril. E. Chemical energy source for muscle contraction. 26. Muscle fibers are composed of parallel bundles of myofibrils. 27. In striated muscle, the longitudinal axis of the fiber is perpendicular to the striations. 28. Thick filaments in vertebrates are composed mostly of a single protein called myosin. 29. The removal of actin monomers at one end of a microfilament, and their addition at the other end is known as treadmilling. 30. True or false. Actin monomers spontaneously assemble into microfilaments. False. 31. True or false. Calcium modulates muscle activity through binding to the thin filament protein troponin C. True. 32. How is muscle contraction stimulated by calcium ions? A. Calcium ions are released from the sarcoplasmic reticulum and bind to troponin C, promoting the binding of myosin to actin. NOTE: The binding of calcium ions by troponin C inititates a series of conformational changes. B. Calcium ions are released from the sarcoplasmic reticulum and bind to tropomyosin, stimulating its ATPase activity. C. Calcium ions are released from the sarcoplasmic reticulum and bind to actin, promoting its binding to myosin. D. Calcium ions are released from the sarcoplasmic reticulum and bind to myosin, stimulating ATPase activity. 33. Select the statement that best matches the following: T lymphocytes, or T cells A. Cells that mediate cellular immunity. B. Antibodies produced by hybridoma cells.

13/15 C. Fragments of proteolyzed IgG that have antigen-binding sites. D. Cells that mediate humoral immunity. E. Diverse group of proteins also known as antibodies. 34. Select the statement that best matches the following: B lymphocytes, or B cells A. Antibodies produced by hybridoma cells. B. Diverse group of proteins also known as antibodies. C. Cells that mediate cellular immunity. D. Fragments of proteolyzed IgG that have antigen-binding sites. E. Cells that mediate humoral immunity. 35. Select the statement that best matches the following: Immunoglobulins A. Fragments of proteolyzed IgG that have antigen-binding sites. B. Cells that mediate humoral immunity. C. Cells that mediate cellular immunity. D. Antibodies produced by hybridoma cells. E. Diverse group of proteins also known as antibodies. 36. Select the statement that best matches the following: Fab fragments A. Fragments of proteolyzed IgG that have antigen-binding sites. B. Cells that mediate cellular immunity. C. Antibodies produced by hybridoma cells. D. Cells that mediate humoral immunity. E. Diverse group of proteins also known as antibodies. 37. Select the statement that best matches the following: Monoclonal antibodies A. Fragments of proteolyzed IgG that have antigen-binding sites.

14/15 B. Cells that mediate cellular immunity. C. Cells that mediate humoral immunity. D. Diverse group of proteins also known as antibodies. E. Antibodies produced by hybridoma cells. 38. The immune response is triggered by the presence of foreign macromolecules, called antigens. 39. IgG is the most common class of immunoglobulins. 40. Autoimmune diseases involve the loss of self-tolerance. 41. True or false. A secondary immune response is less intense than a primary response. False. NOTE: A secondary response is more intense than a primary response. 42. What is the basic subunit structure of immunoglobulins? A. Two identical light chains and two identical heavy chains. NOTE: Some immunoglobulins contain multiple copies of this basic unit. B. Two identical light chains. C. One light chain and one heavy chain. D. Two identical heavy chains. 43. Which of the following statements is not true about IgG? A. The antigen binding sites have an immunoglobulin fold motif (a sandwich composed of three- and four-stranded antiparallel sheets that are linked by a disulfide bond). B. The antigen-binding site is located at the tip of each Fab fragment in a crevice between its VL and VH domains C. The heavy chain of an IgG molecule is composed of four similar domains made of beta sheets.

15/15 D. Has a Y-shaped general structure. E. Has two antigen binding sites that can recognize and bind different antigens. NOTE: The antigen binding sites are identical and bind the same antigen. 44. True or false. The ability of an antibody to recognize antigens resides in three loops in the variable domain of the immunoglobulin fold. The basic immunoglobulin structure must accommodate an enormous variety of antigens. Most of the amino acid variation among antibodies is concentrated in these three short segments, called hypervariable sequences that line an immunoglobulin’s antigen-binding site, so that their amino acids determine its binding specificity. True....