Ch. 7 Wiley Plus
Hemoglobin's subunits bind oxygen in a ___________ manner.
positively cooperative
CO2 binds at the N-terminal amino groups of blood proteins to form carbamates and release ________________.
protons
Sigmoidal binding curves are diagnostic of _______________ interactions between binding sites.
cooperative
Mutations that favor the oxidation of the heme iron(II) to iron(III) can cause _________________.
cyanosis
When oxygen binds to heme, the oxygen forms a hydrogen bond with ____________________.
His E7
Hemoglobin's affinity for oxygen is sensitive to small changes in pH (the Bohr effect). Which of the following amino acid(s) is/are primarily responsible for this? Option A :Histidine residues in the protein's central cavity. Option B :Lysine residues in the protein's central cavity. Option C :The distal histidine.
Option A :Histidine residues in the protein's central cavity.
Which of the following triggers the transition from T state to R state (low to high affinity) in hemoglobin? Option A: oxygen binding. Option B: oxygen dissociation. Option C: movement of the proximal histidine. Option D: heme binding. Option E: subunit dissociation.
Option A: oxygen binding.
If a Lys residue that interacts with 2,3-bisphosphoglycerate (BPG) in the central cavity of hemoglobin is changed to a Ser residue, how would this affect hemoglobin behaviour? Option A :The T state would be less stable. Option B :Oxygen binding would be more sensitive to pH. Option C :Oxygen binding would be less sensitive to pH. Option D :The T state would be more stable.
Option A :The T state would be less stable.
______of the world's human population carries an inherited variant hemoglobin gene. Option A: 5% Option B: 25% Option C: 50% Option D: 75% Option E: 90%
Option A: 5%
Which of the following statements about actin is not true? Option A: Actin is present only as monomers in nonmuscle cells. Option B: Actin is the most abundant cytoplasmic protein in many cell types. Option C: Actin filaments are dynamic, they grow at one end and they lose subunits at the other end. Option D: Actin plays an important role in endocytosis. Option E: Actin forms microfilaments in many cell types.
Option A: Actin is present only as monomers in nonmuscle cells.
Which gas does not bind to the porphyrin ring Fe(II) ion in myoglobin? Option A: CO2 Option B: NO Option C: O2 Option D: H2S Option E: CO
Option A: CO2
Which of the following occurs in hemoglobin when blood pH is lowered? Option A: Histidine side chains at the subunit interface are charged at lower pH, forming salt bridges that stabilize the T state. Option B: Hemoglobin binds BPG with reduced affinity because histidine side chains in the central cavity of hemoglobin are charged at lower pH. Option C: The distal histidine becomes charged at lower pH, resulting in a lower affinity of the heme. Option D: The proximal histidine becomes charged at lower pH, which weakens the binding of heme in its pocket.
Option A: Histidine side chains at the subunit interface are charged at lower pH, forming salt bridges that stabilize the T state.
Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin. Which of the following statements correctly outlines the mechanism behind this observation? Option A: In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity. Option B: In fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with lower affinity. Option C: In fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with greater affinity. Option D: In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with greater affinity.
Option A: In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity.
Which of the following is NOT one of the rules that defines the symmetry model of allosterism? Option A: Ligand binding induces a conformational change in the subunit to which it binds. Option B: An allosteric protein is an oligomer of symmetrically related subunits. Option C: Each subunit can exist in two conformational states, R and T, which are in equilibrium. Option D: The ligand can bind to a subunit in either conformation. Only the conformational change alters the affinity for ligand.
Option A: Ligand binding induces a conformational change in the subunit to which it binds.
Structurally, myoglobin and hemoglobin are very similar proteins. In which of the following levels of structure do they differ most? Option A: Quaternary structure. Option B: Primary structure. Option C: Tertiary structure. Option D: Secondary structure.
Option A: Quaternary structure.
Where are disulfide bonds found in immunoglobulins? Option A: They are found in all of the places listed above. Option B: They link the light chains to the heavy chains. Option C: They are found between the beta sheets in many of the domains. Option D: They link the heavy chains to each other.
Option A: They are found in all of the places listed above.
What is the primary role of nonmuscle actin in eukaryotic cells? Option A: They form microfilaments that are part of the cytoskeleton. Option B: They are stored in organelles, for future use in muscle function. Option C: They are stored to provide a source of energy. Option D: They form a protective barrier on the surface of the cell.
Option A: They form microfilaments that are part of the cytoskeleton.
Max Perutz's investigation of the structure of hemoglobin primarily utilized_____. Option A: X-ray crystallography Option B: genetic engineering Option C: NMR spectroscopy Option D: genomics Option E: mass spectrometry
Option A: X-ray crystallography
Which of the following statements is FALSE? In its interaction with hemoglobin, oxygen is: Option A: a prosthetic group. Option B: a ligand. Option C: reversibly bound. Option D: bound at the 6th coordination position of the Fe(II) ion in the heme. Option E: homoallosteric effector.
Option A: a prosthetic group.
Myoglobin's primary physiological role is to facilitate oxygen ________. Option A: diffusion Option B: reduction Option C: binding Option D: storage Option E: metabolism
Option A: diffusion
Which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function? Option A: histidine Option B: tyrosine Option C: lysine Option D: glutamate Option E: glycine
Option A: histidine
What are the main bonds or forces that stabilize the dimer formed by two myosin heavy chains? Option A: hydrophobic interactions Option B: hydrogen-bonds Option C: ionic interactions Option D: isopeptide bonds Option E: disulfide bonds
Option A: hydrophobic interactions
While the binding of O2 to myoglobin as a function of pO2 is described by a simple __________ curve, the binding to hemoglobin is described by a more complex ______ curve. Option A: hyperbolic; sigmoidal Option B: sigmoidal; hyperbolic Option C: sigmoidal; bell-shaped Option D: hyperbolic; concave Option E: exponential; hyperbolic
Option A: hyperbolic; sigmoidal
Hemoglobin S, the variant responsible for the misshapen red blood cells characteristic of the disease sickle-cell anemia, is potentially advantageous to heterozygotes because it confers some level of resistance to the disease _________. Option A: malaria Option B: polycythemia Option C: AIDS Option D: rickets Option E: cyanosis
Option A: malaria
Noncooperative binding is characterized by a Hill coefficient of what value? Option A: n = 1 Option B: 0 < n < 1 Option C: n = 0 Option D: n > 1
Option A: n = 1
Within the sequence of steps in the Perutz mechanism explaining Hb's cooperative binding of O2, listed following in no particular order, select the position in the order in which the step "His F8 is pulled towards the heme" occurs: - His F8 is pulled towards the heme. - Residues at the α - β interfaces move, and ion pairs involving the C-terminal residues are broken. - Oxygen binds to deoxyhemoglobin. - Helix F tilts and is translated by about 1 Angstrom. - Fe(II) is pulled into the plane of the porphyrin. Option A: third Option B: fourth Option C: fifth Option D: first Option E: second
Option A: third
In sickle-cell anemia, the negatively charged glutamic acid residue is replaced by the neutral amino acid ____________. Option A: valine Option B: adenosine Option C: glycine Option D: lysine Option E: tyrosine
Option A: valine
Carbon monoxide binds to heme: Option A: with a higher affinity than oxygen. Option B: from the side opposite oxygen, resulting in a brown colored heme. Option C: with a lower affinity than oxygen. Option D: resulting in the oxidation of the Fe(II) to Fe(III). Option E: in a manner that displaces carbon dioxide, causing CO2 poisoning.
Option A: with a higher affinity than oxygen.
Hydroxyurea is a treatment for sickle cell anemia that increases the percentage of erythrocytes that contain fetal hemoglobin. Option A:True Option B:False
Option A:True
In mollusks, O2 is transported by hemocyanin. Option A:True Option B:False
Option A:True
In myoglobin, the protein prevents the oxidation of Fe(II) to Fe(III) by oxygen. Option A:True Option B:False
Option A:True
The sequential model of allosterism states that ligand binding induces a conformational change in the subunit to which it binds. Option A:True Option B:False
Option A:True
Which class of antibodies has been implicated in allergic reactions? Option A: IgA Option B: IgE Option C: IgG Option D: IgD Option E: IgM
Option B: IgE
Which of the following statements correctly describes the interaction between an allosteric protein and an allosteric effector? Option A: The effector binds non-specifically to one subunit and through induced fit initiates cooperativity between the subunits. Option B: The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation. Option C: The effector activates the protein by causing it to switch from its T (low affinity) to R (high affinity) form. Option D: The effector binds covalently at a specific site on the protein, causing a global change in shape.
Option B: The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation.
Which of the following statements about the symmetry model of allosterism is not true? Option A: the ligand can bind to a subunit in either conformation. Option B: none of the above. Option C: the oligomer can exist in two conformational states, which are in equilibrium. Option D: the molecular symmetry of the protein is conserved during the conformational change. Option E: the protein is an oligomer of symmetrically (or pseudosymmetrically) related subunits.
Option B: none of the above.
Hemerythrin and hemocyanin are: Option A: tetrameric hemoglobin derivatives containing only α-chains (α4 tetramers). Option B: oxygen transport proteins found in invertebrates. Option C: hemoglobin variants that are found in animals at high altitude. Option D: synthetic derivatives of hemoglobin's heme group used in artificial blood substitutes. Option E: human mutant hemoglobins with decreased oxygen affinity.
Option B: oxygen transport proteins found in invertebrates.
Oxygen is highly soluble in aqueous solution. Option A:True Option B:False
Option B:False
Humoral immunity is mediated by soluble molecules. Which cell type produces the soluble molecules that carry out the humoral immunity? Option A: T cells Option B: monocytes Option C: B cells Option D: macrophages Option E: neutrophils
Option C: B cells
Why is the decreased affinity of fetal hemoglobin for BPG advantageous? Option A: With fewer BPG molecules bound there are more heme residues available for O2 binding. Option B: None of the above. Option C: Decreased BPG binding biases the fetal hemoglobin toward the R state. Option D: BPG is available to bind to fetal myoglobin, helping to release O2 in fetal muscle tissue. Option E: More free BPG is available to bind to adult hemoglobin, resulting in a shift to the R state.
Option C: Decreased BPG binding biases the fetal hemoglobin toward the R state.
During vigorous exercise, the pH of blood passing through skeletal muscle decreases. How does this decrease affect the behaviour of hemoglobin? Option A: It increases O2 binding to hemoglobin, because it decreases the binding of BPG. Option B: It increases O2 binding to hemoglobin, because it increases the binding of BPG. Option C: It decreases O2 binding to hemoglobin, because it increases the binding of BPG. Option D: It decreases O2 binding to hemoglobin, because it decreases the binding of BPG.
Option C: It decreases O2 binding to hemoglobin, because it increases the binding of BPG.
Consider a hypothetical hemoglobin-like molecule with a Hill coefficient (constant) of 1 and the same p50 value as normal hemoglobin. Choose the statement below that best describes the two proteins. Option A: There is a cooperative interaction between oxygen-binding sites in both the hypothetical and normal hemoglobins. Option B: At pO2 less than p50, normal hemoglobin has a greater YO2 value. Option C: The oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for normal hemoglobin is sigmoidal. Option D: The two hemoglobins would be able to deliver about the same amount of oxygen to the tissues. Option E: The hypothetical hemoglobin has a greater oxygen affinity than normal hemoglobin.
Option C: The oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for normal hemoglobin is sigmoidal.
Which of the following statements about the T and R states of hemoglobin is FALSE? Option A: In the R state, the Fe2+ ion lies in the plane of the heme. Option B: The T state has a lower affinity for oxygen than the R state. Option C: The R state has a smaller central cavity than the T state. Option D: The T state is less stable than the R state at lower pH.
Option D: The T state is less stable than the R state at lower pH.
A newly-identified protein shows a sigmoidally-shaped curve in a graph of fractional saturation versus ligand concentration. Which of the following statements about that protein is TRUE? Option A: The ligand binds irreversibly at a specific site on the protein, causing a global change in shape. Option B: When the ligand binds to one subunit, the affinity of the other subunits for the same ligand remains the same. Option C: The protein undergoes conformational changes in quaternary structure when the ligand binds. Option D: The protein does NOT bind the ligand cooperatively.
Option C: The protein undergoes conformational changes in quaternary structure when the ligand binds.
The oxygen binding by hemocyanins is mediated by Option A: a copper atom Option B: an iron ion Option C: a pair of copper atoms Option D: a heme group Option E: a pair of iron ions
Option C: a pair of copper atoms
Muscle contraction is triggered Option A: in response to a decrease in the cytoplasmic cAMP concentration. Option B: in response to an increase in the cytoplasmic cAMP concentration. Option C: in response to an increase in the cytoplasmic Ca2+ concentration. Option D: in response to an increase in the cytoplasmic titin concentration. Option E: in response to a decrease in the cytoplasmic Ca2+ concentration.
Option C: in response to an increase in the cytoplasmic Ca2+ concentration.
Some abnormal hemoglobins have Hill coefficients that are ______ that of normal hemoglobin, indicating that their ability to bind oxygen cooperatively has been compromised. Option A: much greater than Option B: about equal to Option C: less than Option D: greater than Option E: The correct answer cannot be determined from the information given.
Option C: less than
During muscle contraction Option A: actin pulls myosin toward the Z disk. Option B: actin pushes myosin toward the M disk. Option C: myosin pulls actin filaments toward the M disk. Option D: myosin pushes actin filaments toward the Z disk. Option E: All of the answers above are correct.
Option C: myosin pulls actin filaments toward the M disk.
The Bohr effect refers to Option A: the decrease in affinity of Hb for O2 when the BPG concentration goes down Option B: the decrease in affinity of Hb for O2 when the pH goes up Option C: the decrease in affinity of Hb for O2 when the pH goes down Option D: the increase in the affinity of Hb for O2 when the O2 concentration goes up Option E: the decrease in affinity of Hb for O2 when the BPG concentration goes up
Option C: the decrease in affinity of Hb for O2 when the pH goes down
The reaction of carbonic anhydrase catalyzes Option A: the hydration of bicarbonate, resulting in the formation of carbonic acid. Option B: the hydrolysis of carbamates with the concomitant consumption of protons. Option C: the hydration of carbon dioxide, forming bicarbonate and protons. Option D: the formation of carbamates with the concomitant release of protons. Option E: the reduction of carbon dioxide with the concomitant consumption of protons.
Option C: the hydration of carbon dioxide, forming bicarbonate and protons.
During muscle contraction myosin heads Option A: walk along thin filaments toward the M disk. Option B: walk along thick filaments toward the M disk. Option C: walk along the thin filaments toward the Z disk. Option D: walk along thick filaments toward the Z disk. Option E: walk along the thin filaments toward the H zone.
Option C: walk along the thin filaments toward the Z disk.
Myoglobin's secondary structure is primarily composed of ______________. Option A: parallel β-sheets Option B: antiparallel β-sheets Option C: α-helices Option D: polyproline helices Option E: Ω-loops
Option C: α-helices
The Hill plot shows that the fourth oxygen binds to hemoglobin with a ______-fold greater affinity than the first. Option A: 2 Option B: 5 Option C: 10 Option D: 100 Option E: 20
Option D: 100
Hemoglobin is a heterotetramer. How many protomers are present in hemoglobin? Option A: 0 Option B: 1 Option C: 4 Option D: 2 Option E: 3
Option D: 2
he graph shows several oxygen binding curves obtained for hemoglobin (Hb) under different experimental conditions. If curve 3 represents the oxygen binding behaviour of normal adult Hb, which curve represents the oxygen binding behaviour of fetal Hb? Option A: None of the above Option B: 4 Option C: 3 Option D: 2 Option E: 1
Option D: 2
Which of the statements about muscle contraction is correct? Option A: During muscle contraction the I band becomes shorter. Option B: During muscle contraction the H zone becomes shorter. Option C: During muscle contraction the sarcomere becomes shorter. Option D: All of the answers above are correct. Option E: During muscle contraction the distance between the Z disk and the M disk becomes short.
Option D: All of the answers above are correct.
The binding of one O2 to a molecule of hemoglobin results in: Option A: A decrease in hemoglobin's ability to bind a second O2. Option B: Dissociation of the hemoglobin subunits. Option C: The release of any other O2 that may have bound earlier. Option D: An increased affinity for O2 in the remaining subunits (which have not yet bound O2). Option E: The movement of hemoglobin to an organism's muscle tissue.
Option D: An increased affinity for O2 in the remaining subunits (which have not yet bound O2).
How are IgG molecules able to recognize a wide variety of different antigens? Option A: The Fc portion has hypervariable sequences that form the antigen binding site. Option B: Each heavy chain has hypervariable sequences that form the antigen binding site, while the light chains do not vary. Option C: Each light chain has hypervariable sequences that form the antigen binding site, while the heavy chains do not vary. Option D: Both light and heavy chains have hypervariable sequences that form the antigen binding
Option D: Both light and heavy chains have hypervariable sequences that form the antigen binding
Which of the following is not a ligand to the porphyrin ring Fe(II) ion in oxymyoglobin? Option A: Oxygen. Option B: Nitrogen atoms in the porphyrin ring. Option C: All are ligands. Option D: His E7. Option E: His F8.
Option D: His E7.
Protein X binds reversibly to ligand Y such that X + Y ⇄ XY, and the molar concentrations of X, Y and XY are known. Which of the following represents the dissociation constant (K) for this reaction? Option A: K could not be determined with the information provided. Option B: K = [XY]/[X][Y] Option C: K = [XY]/[Y] Option D: K = [X][Y]/[XY] Option E: K = [X] + [Y]/[X + Y]
Option D: K = [X][Y]/[XY]
The Ig fold can be described as a Option A: globular fold composed of α helices. Option B: a coiled-coil. Option C: a globular fold composed of β barrel. Option D: a globular fold composed of a β sandwich. Option E: a globular fold composed of a four helix bundle.
Option D: a globular fold composed of a β sandwich.
Myoglobin and a single chain of hemoglobin have similar ______ structures. Option A: quaternary Option B: secondary Option C: primary Option D: tertiary Option E: none of the above
Option D: tertiary
How many antigen-binding sites are present on an IgM molecule? Option A: 25 Option B: 4 Option C: 2 Option D: 16 Option E: 10
Option E: 10
IgG is one of five classes of antibodies that can be produced by our immune system. IgGs have a molecular mass of approximately 150 kDa, what is their subunit composition? Option A: 4 light chains, 4 heavy chains, and a J chain Option B: 2 light chains, 2 heavy chains, and a J chain Option C: 10 light chains, 10 heavy chains , and a J chain. Option D: 6 light chains, 6 heavy chains, and a J chain Option E: 2 light chains and 2 heavy chains
Option E: 2 light chains and 2 heavy chains
How many different classes of antibodies are produced by the human immune system? Option A: 4 Option B: 3 Option C: 1 Option D: 2 Option E: 5
Option E: 5
Which statement about antigen-binding sites in antibodies is false? Option A: An antigen-binding site on an IgG is formed by the variable region of a light chain and the variable region of a heavy chain. Option B: The antigen-binding site is composed of two Ig folds. Option C: An antigen-binding site on an IgG is formed by the amino-terminal ~110 amino acids of a light chain and the amino terminal ~110 amino acids of a heavy chain. Option D: Antigen-binding specificity is determined by the sequences of the hypervariable sequences in both the light chain and the heavy chain. Option E: Antigen binding specificity is determined exclusively by the sequences in the carboxy-terminal ~110 amino acids in the light chain and the heavy chain.
Option E: Antigen binding specificity is determined exclusively by the sequences in the carboxy-terminal ~110 amino acids in the light chain and the heavy chain.
During the T to R conformational shift, Fe(II) drags the F helix via a bond to the side chain of ________. Option A: Val FG5 Option B: Leu FG3 Option C: Leu F4 Option D: Leu F7 Option E: His F8
Option E: His F8
Which of the following increases the affinity of hemoglobin for O2? Option A: the formation of N-terminal carbamates Option B: an increase in BPG concentration Option C: an increase in CO2 concentration Option D: a decrease in pH Option E: an increase in pH
Option E: an increase in pH
Humoral immunity refers to that part of the immune response that is mediated by Option A: the skin. Option B: antigens. Option C: T lymphocytes. Option D: the thymus. Option E: antibodies.
Option E: antibodies.
Fab fragments can be generated by Option A: reduction of IgG molecules. Option B: oxidation of IgG molecules. Option C: combining two light chains. Option D: combining two heavy chains. Option E: limited digestion of IgG molecules with papain.
Option E: limited digestion of IgG molecules with papain.
The repeating functional unit in a myofibril is called Option A: the H zone. Option B: the A band. Option C: the M disk. Option D: the I band. Option E: the sarcomere.
Option E: the sarcomere.
Sickle cell hemoglobin does not form fibers in the __________ form.
R
In the _____________ state of hemoglobin, the iron ion is out of the plane of the porphyrin ring.
T
An increase in pCO2 causes hemoglobin's affinity for oxygen to _____________.
decrease
The affinity of hemoglobin for the 4th oxygen is about 100 times greater than for the _____________ oxygen.
first
When unstable hemoglobin is degraded; degradation products often cause cell lysis, leading to a condition called _______________.
hemolytic anemia
Most of the amino acid variation among antibodies occurs in three short segments called ________________ sequences.
hypervariable
The absence of 2,3-BPG causes hemoglobin's affinity for oxygen to ____________.
increase
The conversion of hemoglobin from the T to the R state requires breaking of ________________ involving C-terminal residues.
ion pairs
The _____________ model of allosterism requires subunits to change conformation simultaneously.
symmetry