Chapter 7 Part 1

Max Perutz's investigation of the structure of hemoglobin primarily utilized_____. X-ray crystallography NMR spectroscopy genomics mass spectrometry genetic engineering

X-ray crystallography

Carbon monoxide binds to heme: with a higher affinity than oxygen. resulting in the oxidation of the Fe(II) to Fe(III). in a manner that displaces carbon dioxide, causing CO2 poisoning. from the side opposite oxygen, resulting in a brown colored heme. with a lower affinity than oxygen.

with a higher affinity than oxygen.

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 "Fe(II) is pulled into the plane of the porphyrin" occurs: - His F8 is pulled towards the heme. - Residues at the - 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. second third fourth fifth first

second

In sickle-cell anemia, the negatively charged glutamic acid residue is replaced by the neutral amino acid ____________. tyrosine lysine valine adenosine glycine

valine

What is the fractional saturation of myoglobin at pO2 = 7.2 torr, if P50 = 2.8 torr? 0.28 0.50 1.00 0.72

.72

What is the fractional saturation of myoglobin at pO2 = 2.8 torr, if p50 = 2.8 torr? 0.28 0.50 1.00 2.80

0.50 Y = pO2 / (p50 + pO2) = 2.8 / (2.8 + 2.8) = 0.5

The Hill plot shows that the fourth oxygen binds to hemoglobin with a ______-fold greater affinity than the first. 2 5 10 20 100

100

Hemoglobin is a heterotetramer. How many protomers are present in hemoglobin? 0 1 2 3 4

2

______of the world's human population carries an inherited variant hemoglobin gene. 5% 25% 50% 75% 90%

5%

Which of the following statements about 2,3-bisphosphoglycerate (BPG) binding is FALSE? BPG binds less tightly to fetal hemoglobin than to adult hemoglobin, thereby aiding oxygen transfer to a fetus. BPG binds to hemoglobin at one site and lowers hemoglobin's affinity for oxygen at another site. BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen. BPG requires a binding site containing multiple positively charged groups.

BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen. This statement is false. BPG does not affect the affinity of myoglobin for oxygen.

Why is BPG essential for the delivery of O2 to the tissues? BPG stabilizes the R state conformation of hemoglobin. BPG stabilizes O2 binding to hemoglobin. BPG stabilizes the association of hemoglobin subunits. BPG stabilizes the T state conformation of hemoglobin.

BPG stabilizes the T state conformation of hemoglobin. The T state of hemoglobin has lower affinity for oxygen and this enables release of oxygen in the tissues.

What is the type of symmetry that relates the protomers in hemoglobin with respect to each other? C2 C4 D2 D4 Tetrahedral symmetry

C2

Which gas does not bind to the porphyrin ring Fe(II) ion in myoglobin? NO CO CO2 O2 H2S

CO2

Which of the following statements is FALSE with respect to hemoglobin's transition from the T state to the R state? BPG is not required to stabilize the R state. The Fe2+ ion is pulled into the plane of the heme prosthetic group when oxygen binds to hemoglobin in the T state. Helix F changes its secondary structure in response to oxygen binding. Contacts between side chains in the different subunits of hemoglobin change upon binding of oxygen to one subunit.

Helix F changes its secondary structure in response to oxygen binding. This statement is false. While the relative position of Helix F does change in response to oxygen binding, the secondary structure of the helix is unaltered.

Which of the statements below about hemoglobin and myoglobin's oxygen binding is INCORRECT: The p50 of hemoglobin is nearly 10 times higher than that of myoglobin. 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. 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. Myoglobin has a higher affinity for oxygen than hemoglobin. Hemoglobin has a Hill coefficient > 1 whereas myoglobin has a Hill coefficient < 1. 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.

Hemoglobin has a Hill coefficient > 1 whereas myoglobin has a Hill coefficient < 1

Which of the following diseases is not caused by a mutation in hemoglobin? Polycythemia Sickle-cell anemia Hemolytic anemia Hemophilia

Hemophilia

Which of the following is not a ligand to the porphyrin ring Fe(II) ion in oxymyoglobin? His E7. His F8. Nitrogen atoms in the porphyrin ring. Oxygen. All are ligands.

His E7.

During the T to R conformational shift, Fe(II) drags the F helix via a bond to the side chain of ________. Leu F7 Leu F4 His F8 Leu FG3 Val FG5

His F8

Which of the following occurs in hemoglobin when blood pH is lowered? The proximal histidine becomes charged at lower pH, which weakens the binding of heme in its pocket. Histidine side chains at the subunit interface are charged at lower pH, forming salt bridges that stabilize the T state. The distal histidine becomes charged at lower pH, resulting in a lower affinity of the heme. Hemoglobin binds BPG with reduced affinity because histidine side chains in the central cavity of hemoglobin are charged at lower pH.

Histidine side chains at the subunit interface are charged at lower pH, forming salt bridges that stabilize the T state.

What typer of binding curve is represented by oxygen binding to Myoglobin?

Hyperbolic curve

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? K = [X][Y]/[XY] K = [XY]/[X][Y] K = [X] + [Y]/[X + Y] K = [XY]/[Y] K could not be determined with the information provided

K = [X][Y]/[XY]

Which of the following is NOT one of the rules that defines the symmetry model of allosterism? An allosteric protein is an oligomer of symmetrically related subunits. Each subunit can exist in two conformational states, R and T, which are in equilibrium. The ligand can bind to a subunit in either conformation. Only the conformational change alters the affinity for ligand. Ligand binding induces a conformational change in the subunit to which it binds.

Ligand binding induces a conformational change in the subunit to which it binds.

Which of the following statements most accurately explains why hemoglobin is able to deliver oxygen to myoglobin in the tissues? The iron in the heme group of myoglobin is Fe3+, which has a higher affinity for oxygen. Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve. The presence of BPG in the red blood cells shifts the equilibrium towards the R state of hemoglobin. The pH of tissue/muscle is always higher than that of blood, which aids hemoglobin in giving up its oxygen.

Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve. The sigmoidal binding curve illustrates hemoglobin's ability to adopt a low affinity state. This enables it to transfer oxygen to myoglobin which always binds oxygen with high affinit

Which of the following statements is FALSE regarding the interaction of oxygen with myoglobin? Oxygen is a homoallosteric effector of myoglobin. Oxygen binds at the 6th coordination position of the Fe2+ ion in the heme. Oxygen is a ligand of myoglobin. Oxygen binds reversibly and with high affinity to the heme prosthetic group.

Oxygen is a homoallosteric effector of myoglobin. This statement is false. Myoglobin is not an allosteric protein

Structurally, myoglobin and hemoglobin are very similar proteins. In which of the following levels of structure do they differ most? Tertiary structure. Quaternary structure. Primary structure. Secondary structure.

Quaternary structure. Myoglobin does not have quaternary structure whereas hemoglobin does.

Which of the following statements about hemoglobin is TRUE? The affinity of fetal hemoglobin for oxygen is higher than that of maternal hemoglobin. Hemoglobin differs from myoglobin because it contains more β-pleated sheet structure. In the Bohr effect the binding of oxygen to hemoglobin is increased by the presence of H+ ions and CO2. Variations in the primary structure of hemoglobin always result in genetic diseases.

The affinity of fetal hemoglobin for oxygen is higher than that of maternal hemoglobin.

BPG stands for biphenylglycine. boronylphenylglutamate. bisphosphoglycerate. bisphenylglycerol. betapropylglutamine.

bisphosphoglycerate.

The most rapid way that erythrocytes adapt to high altitudes is by producing genetically altered hemoglobins that have higher O2-binding affinities. by adopting the symmetry model of allosterism. by increasing the concentration of hemoglobin. by relying upon the simpler protein myoglobin. by increasing the intracellular concentration of BPG.

by increasing the intracellular concentration of BPG.

Myoglobin's primary physiological role is to facilitate oxygen ________. storage metabolism binding reduction diffusion

diffusion

Which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function? glycine tyrosine histidine lysine glutamate

histidine Histidine residues play several critical roles in hemoglobin function. For example, think of the proximal histidine, the distal histidine, and the histidine residues involved in the binding of 2,3-bisphosphoglycerate (BPG).

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 _________. rickets AIDS cyanosis polycythemia malaria

malaria

Noncooperative binding is characterized by a Hill coefficient of what value? Entry field with correct answer n = 0 n = 1 n > 1 0 < n < 1

n = 1

Which of the following statements about the symmetry model of allosterism is not true? the protein is an oligomer of symmetrically (or pseudosymmetrically) related subunits. the oligomer can exist in two conformational states, which are in equilibrium. the ligand can bind to a subunit in either conformation. the molecular symmetry of the protein is conserved during the conformational change. none of the above.

none of the above.

Hemoglobin's p50 value is about ______ as great as myoglobin's p50 value. Entry field with correct answer one-tenth half twice ten times twenty times

ten times

When the partial pressure of O2 in venous blood is 30 torr, the saturation of myoglobin with O2 is ______ while the saturation of hemoglobin with O2 is ______. 0.55, 0.91 0.91, 0.55 2.8 torr, 26 torr 0.91, 0.97 none of the above

0.91, 0.55

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. sigmoidal; hyperbolic hyperbolic; sigmoidal exponential; hyperbolic sigmoidal; bell-shaped hyperbolic; concave

hyperbolic; sigmoidal

In what direction does the sigmoidal curve shift due to an increase in pH?

The sigmoidal curve is shifted to the left.

Why does the concentration of BPG in red blood cells increase when humans are exposed to high altitudes? To allow hemoglobin to bind more oxygen at lower partial pressures of oxygen. To induce the production of more red blood cells. To neutralize the increased concentration of hydrogen ions produced when muscle works harder at high altitudes. To allow hemoglobin to release more oxygen at lower partial pressures of oxygen.

To allow hemoglobin to release more oxygen at lower partial pressures of oxygen. When the partial pressure of oxygen in the lungs is low, the oxygen-saturation of hemoglobin is reduced. This means that there is less total oxygen available for release in the tissues. One way to compensate for this shortfall is to ensure that hemoglobin releases relatively more oxygen in the tissues than usual and this is achieved by increasing the concentration of BPG in the red blood cells.

The Bohr effect refers to the decrease in affinity of Hb for O2 when the pH goes down the decrease in affinity of Hb for O2 when the pH goes up the increase in the affinity of Hb for O2 when the O2 concentration goes up the decrease in affinity of Hb for O2 when the BPG concentration goes up the decrease in affinity of Hb for O2 when the BPG concentration goes down

the decrease in affinity of Hb for O2 when the pH goes down

The binding of one O2 to a molecule of hemoglobin results in: A decrease in hemoglobin's ability to bind a second O2. The release of any other O2 that may have bound earlier. Dissociation of the hemoglobin subunits. The movement of hemoglobin to an organism's muscle tissue. An increased affinity for O2 in the remaining subunits (which have not yet bound O2).

An increased affinity for O2 in the remaining subunits (which have not yet bound O2). When hemoglobin is in the T state, binding of oxygen to one subunit triggers a global change in conformation. This increases the affinity of the remaining subunits for oxygen

Why is the decreased affinity of fetal hemoglobin for BPG advantageous? With fewer BPG molecules bound there are more heme residues available for O2 binding. Decreased BPG binding biases the fetal hemoglobin toward the R state. More free BPG is available to bind to adult hemoglobin, resulting in a shift to the R state. BPG is available to bind to fetal myoglobin, helping to release O2 in fetal muscle tissue. None of the above.

Decreased BPG binding biases the fetal hemoglobin toward the R state.

Which of the following statements is FALSE? As pH decreases, the O2 binding curve of hemoglobin shifts to the right, because a greater proportion of hemoglobin molecules exist in the T-state at a given pO2. Actively respiring tissues have a relatively low pH and low pO2, which favors the T-state of hemoglobin. In fetal hemoglobin the central cavity is lined with more histidines than in adult hemoglobin, which results in preferential stabilization of the R-state. Fetal hemoglobin has a weaker affinity for BPG than maternal hemoglobin, resulting in a shift of the oxygen-binding curve to the left.

In fetal hemoglobin the central cavity is lined with more histidines than in adult hemoglobin, which results in preferential stabilization of the R-state This statement is false. Fetal hemoglobin has fewer histidine residues positioned in the central cavity than adult hemoglobin and this results in preferential stabilization of the R-state

Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin. Which of the following statements correctly outlines the mechanism behind this observation? In fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with lower affinity. In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity. In fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with greater affinity. In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with greater affinity.

In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity. The mutation of His143 to Ser143 reduces the number of positively charged groups available to form salt bridges with BPG. This reduces the affinity of hemoglobin for BPG and thus the T (low-affinity) state of hemoglobin is less stable.

Which term best describes the histidine F8 residue in myoglobin and hemoglobin? Variable residue. Conservatively substituted residue. Catalytic residue. Invariant residue. Homologous residue.

Invariant residue.

During vigorous exercise, the pH of blood passing through skeletal muscle decreases. How does this decrease affect the behaviour of hemoglobin? It decreases O2 binding to hemoglobin, because it decreases the binding of BPG. It increases O2 binding to hemoglobin, because it increases the binding of BPG. It decreases O2 binding to hemoglobin, because it increases the binding of BPG. It increases O2 binding to hemoglobin, because it decreases the binding of BPG.

It decreases O2 binding to hemoglobin, because it increases the binding of BPG. As pH decreases, certain histidine side chains become positively charged and hemoglobin binds more BPG. This stabilizes the T state of the protein and decreases O2 binding (% saturation).

Which of the following is TRUE about the distal histidine of hemoglobin? It is not conserved in myoglobin. It forms a strong covalent bond with the Fe2+ atom coordinated by heme. It prevents helix F from moving in response to oxygen binding. It forms a hydrogen bond with bound oxygen. It covalently bonds heme into the hemoglobin subunit.

It forms a hydrogen bond with bound oxygen. The distal histidine (His E7) has no affect on helix F. It is the proximal histidine that forms the coordination bond with the iron in the heme.

Shown below are statements matching scientists with their accomplishments. Which of the statements below is INCORRECT: Entry field with correct answer Joseph Barcroft: In 1921 he anticipated the existence of BPG as a factor that decreased the oxygen affinity of hemoglobin. Christian Bohr: In 1904 he reported the release of protons upon oxygen binding by hemoglobin. 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. Daniel Koshland: Proposed the sequential model of allosterism. Jacques Monod: Formulated the symmetry model of allosterism along with Jeffries Wyman and Jean-Pierre Changeux.

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. Linus Pauling did this

Which of the following statements about the structure of myoglobin is FALSE? A heme prosthetic group is tightly bound to myoglobin via a coordination bond. Myoglobin contains all three types of secondary structure. Myoglobin contains a heme prosthetic group that is slotted into a hydrophobic pocket between -helix E and -helix F. The tertiary structure of myogobin is a compact, roughly spherical shape

Myoglobin contains all three types of secondary structure. Myoglobin contains only two types of secondary structure, -helices and loops. It contains no β-sheet

Which of the following statements about sickle cell anemia is FALSE? In sickle cell anemia, hemoglobin molecules aggregate to form long fibers that distort the shape of the red blood cell. The mutation in sickle cell anemia replaces a hydrophilic surface residue with a non-polar residue. Sickle cell anemia is a consequence of a conservative mutation in the β-globin gene. Sickle cell anemia is a genetic disease.

Sickle cell anemia is a consequence of a conservative mutation in the β-globin gene. A mutation that significantly affects the folding or function of a protein cannot be considered conservative

What are the two conformations of hemoglobin? The T state (the conformation of deoxyhemoglobin) and the R state (the conformation of oxyhemoglobin). The R state (the conformation of deoxyhemoglobin) and the T state (the conformation of oxyhemoglobin). The T state (the conformation of dideoxyhemoglobin) and the R state (the conformation of deoxyhemoglobin). The T state (the conformation of myoglobin) and the R state (the conformation of deoxyhemoglobin).

The T state (the conformation of deoxyhemoglobin) and the R state (the conformation of oxyhemoglobin).

Which of the following statements about the T and R states of hemoglobin is FALSE? The R state has a smaller central cavity than the T state. In the R state, the Fe2+ ion lies in the plane of the heme. The T state is less stable than the R state at lower pH. The T state has a lower affinity for oxygen than the R state.

The T state is less stable than the R state at lower pH. This statement is false. Lower pH reflects an increased concentration of H+ ions, and the T state of hemoglobin is stabilized under these conditions.

In what direction does an increase in BPG push the binding curve of oxygen to hemoglobin?

The curve is shifted to the right Red blood cells will produce more BPG so that they can release more oxygen at higher partial pressures of oxygen.

One of the adaptations to high altitude is an increase in the concentration of BPG in red blood cells. What effect does this have on the oxygen binding curve of hemoglobin and why? The curve is shifted to the left because hemoglobin has a lower K (dissociation constant). The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen. The curve is shifted to the right, because hemoglobin has tighter oxygen binding. The curve is shifted to the left because hemoglobin binds oxygen more tightly.

The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen.

Which of the following is NOT a role of histidine in hemoglobin? Protonated histidine residues aid in BPG binding. The distal histidine occupies the 6th coordination position of Fe2+. Histidine residues become protonated as part of the Bohr effect. The proximal histidine occupies the 5th coordination position of Fe2+

The distal histidine occupies the 6th coordination position of Fe2+ This statement does not describe a role for histidine in hemoglobin. The 6th coordination position of the Fe(II) ion is occupied reversibly by oxygen.

Which of the following statements correctly describes the interaction between an allosteric protein and an allosteric effector? The effector binds non-specifically to one subunit and through induced fit initiates cooperativity between the subunits. The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation. The effector activates the protein by causing it to switch from its T (low affinity) to R (high affinity) form. The effector binds covalently at a specific site on the protein, causing a global change in shape.

The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation.

Which of the statements below about hemoglobin's oxygen binding is INCORRECT: Entry field with correct answer 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. 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. 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. 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. 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. The T --> R transition in hemoglobin subunits explains the difference in the oxygen affinities of oxy- and deoxyhemoglobin. 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.

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. The false statement is "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." In fact, because of the beneficial effects of positive cooperativity, the fourth O2 molecule binds with 100-fold greater affinity than the first.

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. There is a cooperative interaction between oxygen-binding sites in both the hypothetical and normal hemoglobins. The hypothetical hemoglobin has a greater oxygen affinity than normal hemoglobin. The oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for normal hemoglobin is sigmoidal. The two hemoglobins would be able to deliver about the same amount of oxygen to the tissues. At pO2 less than p50, normal hemoglobin has a greater YO2 value.

The oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for normal hemoglobin is sigmoidal.

A newly-identified protein has a sigmoidal curve in a graph of fractional saturation versus ligand concentration. What can be deduced about this protein? The protein has primary, secondary and tertiary structure, but not quaternary. The protein binds the ligand cooperatively. The protein has a constant high affinity for the ligand. The dissociation constant (K) of the ligand is low.

The protein binds the ligand cooperatively. A sigmoidal-shaped binding curve typically indicates cooperative binding behaviour

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? Entry field with correct answer The protein does NOT bind the ligand cooperatively. The protein undergoes conformational changes in quaternary structure when the ligand binds. When the ligand binds to one subunit, the affinity of the other subunits for the same ligand remains the same. The ligand binds irreversibly at a specific site on the protein, causing a global change in shape.

The protein undergoes conformational changes in quaternary structure when the ligand binds.

If hemoglobin is in the 'T' state, what is the first component of the peptide chain that moves in response to oxygen binding? The heme group The Fe2+ ion The proximal histidine The distal histidine

The proximal histidine

The oxygen binding by hemocyanins is mediated by an iron ion a pair of iron ions a heme group a copper atom a pair of copper atoms

a pair of copper atoms

Which of the following statements is FALSE? In its interaction with hemoglobin, oxygen is: reversibly bound. homoallosteric effector. a prosthetic group. bound at the 6th coordination position of the Fe(II) ion in the heme. a ligand.

a prosthetic group.

Myoglobin's secondary structure is primarily composed of ______________. parallel β-sheets antiparallel β-sheets a-helices Ω-loops polyproline helices

a-helices

Which of the following increases the affinity of hemoglobin for O2? an increase in BPG concentration the formation of N-terminal carbamates an increase in pH a decrease in pH an increase in CO2 concentration

an increase in pH

If the gene for myoglobin is "knocked out" in mice, the mice: have larger lungs. respire extremely rapidly have dark brown muscle tissue. appear normal, with lighter colored muscle tissue. have their growth stunted.

appear normal, with lighter colored muscle tissue. have their growth stunted.

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 "Residues at the alpha-beta interfaces move, and ion pairs involving the C-terminal residues are broken" occurs: - His F8 is pulled towards the heme. - Residues at the - 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. fourth third fifth second first

fifth

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 "Oxygen binds to deoxyhemoglobin" occurs: - His F8 is pulled towards the heme. - Residues at the - 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. Entry field with correct answer second third fourth fifth first

first

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 "Helix F tilts and is translated by about 1 Angstrom" occurs: - His F8 is pulled towards the heme. - Residues at the - 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. first fourth fifth second third

fourth

The rearrangement of T state hemoglobin to the R state occurs in each protein subunit independently when its heme binds oxygen. requires the binding of at least three oxygen molecules. increases the ion pairing interactions of the C-terminal amino acids. involves the movement of the Fe(II) into the heme plane. opens a central cavity for BPG binding.

involves the movement of the Fe(II) into the heme plane.

Which of the following triggers the transition from T state to R state (low to high affinity) in hemoglobin? oxygen binding. oxygen dissociation. subunit dissociation. movement of the proximal histidine. heme binding.

oxygen binding. When oxygen binds to the Fe(II) ion in the heme ring, at its 6th coordination position, the Fe(II) ion is pulled into the plane of the heme ring. It is this binding interaction that initiates the transition from T to R state.

Hemerythrin and hemocyanin are: human mutant hemoglobins with decreased oxygen affinity. hemoglobin variants that are found in animals at high altitude. synthetic derivatives of hemoglobin's heme group used in artificial blood substitutes. oxygen transport proteins found in invertebrates. tetrameric hemoglobin derivatives containing only -chains (4 tetramers).

oxygen transport proteins found in invertebrates.

Myoglobin and a single chain of hemoglobin have similar ______ structures. primary secondary tertiary quaternary none of the above

tertiary

The reaction of carbonic anhydrase catalyzes the formation of carbamates with the concomitant release of protons. the hydration of bicarbonate, resulting in the formation of carbonic acid. the reduction of carbon dioxide with the concomitant consumption of protons. the hydration of carbon dioxide, forming bicarbonate and protons. the hydrolysis of carbamates with the concomitant consumption of protons.

the hydration of carbon dioxide, forming bicarbonate and protons.

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 - 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. third fifth first second fourth

third

The value of n, the Hill constant (coefficient), for hemoglobin is about ______ as great as the value for myoglobin. half twice three times five times ten times

three times