If hemoglobin is in the T state, what happens at one -subunit when the other -subunit binds oxygen?
-It maintains the T state until its ?-subunit binds oxygen.
-Its N-terminal becomes protonated.
-Its F-helix moves.
-It decreases its affinity for oxygen.
Its F-helix moves
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 binds oxygen more tig
The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen.
Which of the following statements about hemoglobin is TRUE?
-In the Bohr effect the binding of oxygen to hemoglobin is increased by the presence of H+ ions and CO2.
-Hemoglobin differs from myoglobin because it contains more ?-pleated sheet structure.
-Th
The affinity of fetal hemoglobin for -oxygen is higher than that of maternal hemoglobin
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
BPG stabilizes the T state conformation of hemoglobin.
Which of the following is a role of histidine in myoglobin?
-A histidine residue occupies the 6th coordination position of Fe2+.
-A histidine residue forms a hydrogen bond with oxygen.
-Histidine residues become protonated as part of the Bohr effect.
-Pro
A histidine residue forms a hydrogen bond with oxygen.
Protein X binds reversibly to ligand Y such that X + YXY, and the molar concentrations of X, Y and XY are known. Which of the following represents the dissociation constant (Kd) for this reaction?
-Kd = [X][Y]/[XY]
-Kd could not be determined with the inf
Kd = [X][Y]/[XY]
What happens when hemoglobin is converted from the deoxy (T) form to the oxy (R) form?
-The heme becomes slightly dome-shaped and the iron lies out of the plane of the heme.
-The central cavity becomes smaller.
-The iron in heme is oxidized from Fe2+ to F
The central cavity becomes smaller.
The binding of one O2 to a molecule of hemoglobin results in:
-A decrease in hemoglobin's ability to bind a second O2.
-An increased affinity for O2 in the remaining subunits (which have not yet bound O2).
-Dissociation of the hemoglobin subunits.
-The re
An increased affinity for O2 in the remaining subunits (which have not yet bound O2).
Which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function?
histidine
lysine
glycine
glutamate
tyrosine
histidine
Which of the following statements about the T and R states of hemoglobin is FALSE?
-In the R state, the Fe2+ ion lies in the plane of the heme.
-The R state has a smaller central cavity than the T state.
-The T state has a lower affinity for oxygen than t
The T state is less stable than the R state at lower pH.
Which term best describes the histidine F8 residue in myoglobin and hemoglobin?
-Conservatively substituted residue.
-Homologous residue.
-Catalytic residue.
-Variable residue.
-Invariant residue
Invariant residue
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 requires a binding site containing multiple posit
BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen.
Which of the following statements is FALSE with respect to hemoglobin's transition from the T state to the R state?
-Contacts between side chains in the different subunits of hemoglobin change upon binding of oxygen to one subunit.
-Helix F changes its se
Helix F changes its secondary structure in response to oxygen binding.
Which of the following statements about 2,3 bisphosphoglycerate (BPG) is TRUE?
-BPG lowers myoglobin's affinity for oxygen.
-BPG binds more tightly to fetal hemoglobin than to adult hemoglobin.
-BPG binds at a site which contains multiple negatively-charg
The affinity of BPG binding to Hb would be reduced if the N-terminal groups of the four subunits were modified to make them uncharged.
Which of the following statements correctly describes the interaction between an allosteric protein and an allosteric effector?
-The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation.
-The
The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation.
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?
-Oxygen binding would be less sensitive to pH.
-Oxygen binding would be more se
The T state would be less stable.
Which of the statements below about hemoglobin is INCORRECT:
-Hemoglobin is a tetramer made up of myoglobin-like subunits.
-It has been dubbed an "honorary enzyme" even though it functions in oxygen transport and does not catalyze a chemical reaction.
-Th
Subunit interfaces in hemoglobin are composed of predominantly salt bridges.
Which of the statements below about hemoglobin and myoglobin's oxygen binding is INCORRECT:
-Myoglobin has a higher affinity for oxygen than hemoglobin.
-The Hill coefficient (n) increases with the degree of cooperativity of a reaction: A Hill coefficient
Hemoglobin has a Hill coefficient > 1 whereas myoglobin has a Hill coefficient < 1.
Which of the statements below about hemoglobin's oxygen binding is INCORRECT:
-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 a
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.
Which of the following statements about factors relating to the Bohr effect and the effect on CO2 on oxygen transport is NOT true:
-CO2 modulates O2 binding to hemoglobin by combining reversibly with the N-terminal groups of other blood proteins to form c
CO2 modulates O2 binding to hemoglobin by combining reversibly with the N-terminal groups of other blood proteins to form carbonates. The protons released in this reaction promote further O2 release through the Bohr effect.
Which of the following statments about Sickle Cell anemia is INCORRECT?
-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 S has a lower affinity for oxygen than normal adult hemoglobin (hemoglobin A).
Which of the following statements about diseases of hemoglobin and the blood is not true:
-Mutations to that destabilize hemoglobin's tertiary or quaternary structure, alter its oxygen-binding affinity (p50) and reduce its cooperativity result in diseased
Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition.
What is the fractional saturation of myoglobin at pO2 = 2.8 torr, if p50 = 2.8 torr?
0.50
0.28
1.00
2.80
0.50
Noncooperative binding is characterized by a Hill coefficient of what value?
0 < n < 1
n > 1
n = 0
n = 1
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 towa
third
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 involvin
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 toward
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
fourth
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
second
What is the fractional saturation of myoglobin at pO2 = 7.2 torr, if P50 = 2.8 torr?
1.00
0.50
0.72
0.28
0.72
Which gas does not bind to the porphyrin ring Fe2+ ion in myoglobin?
H2S
NO
CO
CO2
O2
CO2
Which of the following statements does not apply to the K value in the equation for the oxygen binding curve of myoglobin?
-It is defined as that oxygen partial pressure at which half of the oxygen binding sites are occupied.
-It is the value of pO2 at wh
If Y > K, then myoglobin is less than 50% saturated with oxygen.
Myoglobin and a single chain of hemoglobin have similar ______ structures.
primary
secondary
tertiary
quaternary
none of the above
tertiary
Hemoglobin's p50 value is about ______ as great as myoglobin's p50 value.
twice
one-tenth
half
ten times
twenty times
ten times
The value of n in the Hill equation for hemoglobin is about ______ as great as the value for myoglobin.
three times
half
ten times
twice
five times
three times
Consider a hypothetical hemoglobin with a Hill coefficient of 1 and the same p50 value as normal hemoglobin. Choose the statement below that best describes the two proteins.
-The two hemoglobins would be able to deliver about the same amount of oxygen to
The oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for normal hemoglobin is sigmoidal.
Some abnormal hemoglobins have Hill coefficients that are ______ that of normal hemoglobin, indicating that their ability to bind oxygen cooperatively has been compromised.
-about equal to
-much greater than
-cannot be determined from the information give
less than
The Hill plot shows that the fourth oxygen binds to hemoglobin with ______-fold greater affinity than the first.
5
100
10
2
20
100
Myoglobin's secondary structure is primarily composed of ______________.
-alpha-helices
-parallel beta-sheets
-antiparallel beta-sheets
-alpha-bends
-beta-helices
-alpha-helices
Myoglobin's primary physiological role is to facilitate oxygen ________.
binding
storage
reduction
diffusion
metabolism
diffusion
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
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 a constant high affinity for the ligand.
-The protein has primary, secondary and ter
The protein binds the ligand cooperatively
What type of allosteric effector is BPG?
-A homoallosteric effector of myoglobin.
-A homoallosteric effector of hemoglobin.
-A heteroallosteric effector of myoglobin.
-A heteroallosteric effector of hemoglobin.
-Both C and D are correct
A heteroallosteric effector of hemoglobin
Which of the following is NOT a role of histidine in hemoglobin?
-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
The distal histidine occupies the 6th coordination position of Fe2+
Why is hemoglobin's affinity for oxygen sensitive to small changes in pH (the Bohr effect)?
-Histidine side chains in the central cavity of hemoglobin are charged at lower pH, decreasing BPG binding.
-The affinity of the proximal histidine for the heme Fe
Histidine side chains in hemoglobin become charged at lower pH forming salt bridges that stabilize the T state.
If the gene for myoglobin is knocked out in mice, the mice:
-respire extremely rapidly.
-have larger lungs.
-appear normal, with lighter colored muscle tissue.
-have their growth stunted.
-have dark brown muscle tissue
appear normal, with lighter colored muscle tissue.
Carbon monoxide binds to Heme:
-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 higher affinity than oxygen
with a higher affinity than oxygen.
In sickle-cell anemia, the negatively charged glutamic acid residue is replaced by the neutral amino acid ____________.
glycine
tyrosine
valine
adenosine
lysine
valine
The most rapid way that erythrocytes adapt to high altitudes is:
-by producing genetically altered hemoglobins that have higher O2--binding affinities.
-by increasing the intracellular concentration of BPG.
-by adopting the symmetry model of allosterism.
by increasing the intracellular concentration of BPG.
Hemerythrin and hemocyanin are:
-synthetic derivatives of hemoglobin's heme group used in artificial blood substitutes.
-oxygen transport proteins found in invertebrates.
-hemoglobin variants that are found in animals at high altitude.
-tetrameric hemoglo
oxygen transport proteins found in invertebrates
The rearrangement of T-form hemoglobin to the R-form:
-increases the ion pairing interactions of the C-terminal amino acids.
-opens a central cavity for BPG binding.
-occurs in each protein subunit independently when its heme binds oxygen.
-requires the b
involves the movement of the Fe(II) into the heme plane.
While the binding of O2 to myoglobin as a function of pO2 is described by a simple __________ curve, thebinding to hemoglobin is described by a more complex ______ curve.
-exponential; hyperbolic
-hyperbolic; sigmoidal
-sigmoidal; bell-shaped
-hyperbolic;
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 _________.
cyanosis
AIDS
poly
malaria
BPG stands for:
bisphenylglycerol
betapropylglutamine
boronylphenylglutamate
bisphosphoglycerate
biphenylglycine
bisphosphoglycerate
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 availab
Decreased BPG binding biases the fetal hemoglobin toward the R state.
The reaction of carbonic anhydrase catalyzes:
-the hydration of bicarbonate, resulting in the formation of carbonic acid
-the hydrolysis of carbamates with the concomitant consumption of protons
-the hydration of carbon dioxide, forming bicarbonate and pr
the hydration of carbon dioxide, forming bicarbonate and protons
During the T to R conformational shift, Fe(II) drags the F-helix via a bond to the side chain of ________.
His F8
Leu FG3
Val FG5
Leu F7
Leu F4
His F8
If the binding of O2 to hemoglobin was characterized by a Hill constant of -1:
-the sequential model of allosterism would be eliminated as a reasonable model.
-the binding of the first O2 would increase the affinity of the hemoglobin for O2.
-hemoglobin w
the binding of the first O2 would decrease the affinity of the hemoglobin for O2.
______ of the world's human population carry a variant hemoglobin.
75%
90%
25%
5%
50%
5%