Myoglobin and hemoglobin each have different numbers of subunits and this affects their respective
oxygen storage and delivery capabilities. How many subunits do myoglobin and hemoglobin each have?
Select one:
a. Two,
...
Myoglobin and hemoglobin each have different numbers of subunits and this affects their respective
oxygen storage and delivery capabilities. How many subunits do myoglobin and hemoglobin each have?
Select one:
a. Two, Three
b. One, Two
c. One, Four Correct! Myoglobin consist of one and hemoglobin consists of four subunits. The number
of subunits affects their respective oxygen storage and delivery capabilities.
d. Four, One
Addition of ______________________alters the shape of the iron–heme complex, and therefore its
absorption of light as indicated by its color change from dark purple (the color of hemoglobin in venous
blood) to brilliant scarlet (the color of hemoglobin in arterial blood).
Select one:
a. iron
b. oxygen Correct!
c. globin subunit
d. porphyrin
Oxygen binding alters the structure of an entire hemoglobin tetramer, so the structures of oxyhemoglobin
and deoxyhemoglobin are noticeably different. The oxyhemoglobin conformation is specifically referred
to as the __________ state, whereas the deoxyhemoglobin conformation is referred to as the __________
state.
Select one:
a. O and D
b. Oxygenated and Deoxygenated
c. Relaxed or R and Tense or T Correct! Oxygen binding causes a marked change in hemoglobin
structure. In the presence of oxygen, hemoglobin is in the Relaxed state or R state. In the absence of
oxygen, hemoglobin is in the Tense state or T state.
d. There is no difference between the two states
Patients with sickle cell anemia have atypical hemoglobin, which will distort the red blood cells into
sickle shape during oxygen delivery. The substitution of a hydrophilic amino acid with a
____________amino acid in hemoglobin subunits results in the polymerization of hemoglobin, leading to
the sickling of red blood cells.
Select one:
a. hydrophobic Correct! In case of sickle cell anemia, a hydrophilic amino acid-glutamate is replaced by
a non polar-hydrophobic amino acid-valine, leading to polymerization of hemoglobin, fibril formation
and eventually sickling of the red blood cells.
b. cysteine
c. polar
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d. hydrophilic
Hemglobin consists of four proteins subunits. Each subunit contains a heme group that holds an iron
atom, which can bind to an oxygen molecule.
When binding hemoglobin or myoglobin, CO binds in place of _________.
Select one:
a. Iron
b. Oxygen Correct! CO binds in place of oxygen.
c. Histidine
d. Heme
Structurally, hemoglobin can bind ___ molecules of oxygen, all of which could potentially be replaced by
carbon monoxide.
Select one:
a. 4 Correct!
b. 2
c. 1
d. 3
Carbon monoxide outcompetes oxygen for attachment to the __________ group of hemoglobin where it
is permanently, covalently attached.
Select one:
a. histidine
b. sulfide
c. ligand
d. heme Correct
As carbon monoxide binds to hemoglobin, the protein subunits change conformation to allow carbon
monoxide to bind faster. This process is called __________.
Select one:
a. positive cooperativity Correct! Binding of one carbon monoxide molecule changes the conformation
of the hemoglobin in a fashion such that more molecules of carbon monoxide can bind to the same
protein.
b. competitive inhibition
c. non-competitive inhibition
d. allosteric binding
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Carbon monoxide shifts the Oxygen-Hemoglobin Dissociation Curve to the left, while carbon dioxide
shifts this curve to the right. Based on your knowledge of the Bohr Effect, which of the following
statements is true?
Select one:
a. Carbon dioxide and carbon monoxide decrease hemoglobin’s affinity for oxygen. Incorrect.
b. Carbon dioxide and carbon monoxide have no impact on hemoglobin’s affinity for oxygen.
c. Carbon dioxide increases hemoglobin’s affinity for oxygen, while carbon monoxide decreases it.
d. Carbon dioxide decreases hemoglobin’s affinity for oxygen, while carbon monoxide increases it
Carbon dioxide, released by the respiring cells, combines with the water molecules of plasma to form
carbonic acid. Carbonic acid increases the H+ ion concentration (low or acidic pH). H+ ions stabilize the
deoxy-conformation (T state) of hemoglobin and allow oxygen release and delivery to the tissues. On the
other hand, carbon monoxide, which has a very high affinity for hemoglobin than oxygen, binds and
maintains hemoglobin in oxy-conformation (R state). Oxy-conformation of HB is amenable to further
binding of carbon monoxide and shifts the Oxygen-Hemoglobin Dissociation Curve to the left.
Hemoglobin’s cooperative binding behavior is key to its physiological function. The binding of which of
the following molecules influences this behavior?
Select one:
a. Heme
b. None of these
c. Oxygen Correct!
d. Iron
Carbonic anhydrase is an important __________ present in the red blood cells that aids in efficient
transportation of carbon dioxide in the form of _________, from tissues to lungs.
Select one:
a. enzyme, carbon dioxide
b. chemical, carbon monoxide
c. substrate, bicarbonate ions
d. enzyme, bicarbonate ions Correct! Carbonic anhydrase is an enzyme which catalyzes the conversion
of carbon dioxide to bicarbonate ions. This mechanism enables efficient transport of carbon dioxide by
warding off bubble formation in the blood.
Hemoglobin’s ability to bind or release oxygen depends on the pH of the environment. This behavior is
known as the Bohr effect. Considering this, which of the following statements is true?
Select one:
a. At high pH hemoglobin is able to bind and release oxygen. IncorrectIncorrect.
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b. Hemoglobin binds to the oxygen at low pH and releases oxygen at high pH.
c. At low pH hemoglobin is able to bind and release oxygen.
d. Hemoglobin binds to the oxygen at high pH and releases oxygen at low pH.
pH is a measure of H+ ion concentration. High pH indicates a more basic environment in which the
H+ ion concentration is low, as seen in the lungs. Under these conditions, hemoglobin binds more
oxygen. Low pH indicates an acidic environment in which the H+ ion concentration is high. Such
conditions encourage the binding of H+ ions to hemoglobin and stabilizing a form of hemoglobin
which decreases the affinity for oxygen, resulting in release of oxygen.
Hemoglobin acts as a buffer and controls the pH of the blood by binding to __________.
Select one:
a. H+ ions Correct! A high concentration of H+ ions, if left unbound, will result in an acidic environment
(low pH value). Hemoglobin by binding
b. oxygen
c. bicarbonate ion
d. carbon dioxide
In the lungs, the CO2 concentration is low and the pH is high, while in the tissues, the CO2 concentration
is high and the pH is low.
In locations where the pH is low, hemoglobin will be in the T state, allowing it to release oxygen more
effectively.
Increased levels of 2,3-BPG will decrease the affinity for oxygen by binding to and stabilizing the T
state of hemoglobin. The action of 2,3-BPG allows hemoglobin to release oxygen more effectively, which
is similar to the effect of low pH on the action of hemoglobin.
In comparison to adult hemoglobin, fetal hemoglobin has a higher affinity for oxygen because it doesn’t
bind 2-3BPG well.
Which statement about hemoglobin binding to carbon monoxide (CO) is true?
Select one:
a. Hb binds to CO with a lower affinity than oxygen and stabilizes the R state.
b. Hb binds to CO with a higher affinity than oxygen and stabilizes the T state. Incorrect. CO has a higher
affinity for hemoglobin than oxygen, and this binding stabilizes the R state. This means that any oxygen
that does bind to hemoglobin remains bound and is therefore unavailable to the body's cells.
c. Hb binds to CO with a higher affinity than oxygen and stabilizes the R state.
d. Hb binds to CO with a lower affinity than oxygen and stabilizes the T state.
When hemoglobin changes from T to R, it has ________ affinity for oxygen.
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Select one:
a. zero
b. low Incorrect. The R state has a higher affinity for oxygen than the T state.
c. high
d. none of these are correct
When hemoglobin changes from R to T, it has _______________ affinity for oxygen.
Select one:
a. low
b. high Incorrect. The T state has a lower affinity for oxygen than the R state.
c. zero
d. none of these are correct
Cooperativity refers to _____.
Select one:
a. the exchange of oxygen that happens in the placenta between maternal and fetal blood
b. The ability of hemoglobin to supply the RBC with oxygen for ATP production
c. hemoglobin structural changes that increase its affinity for oxygen. Correct! The four subunits of
hemoglobin, along with the heme groups, communicate or "cooperate" with each other to increase
hemoglobin's affinity for oxygen. When oxygen binds to the iron atom in a heme group, the heme
changes from a bent to a planar state. The change in the heme shape also "tugs" on the protein chain
holding the heme group, causing a conformational shift in the protein subunit. Once one subunit has
undergone the conformational shift, it influences the conformations of the neighboring subunits such that
oxygen binding occurs more easily.
d. The increased affinity for oxygen that myoglobin has when oxygen concentration is low
When the oxygen concentration is high, the heme shape is _____________. When the oxygen
concentration is low, the heme shape is ______________shape.
Select one:
a. bent (non-planar), bent (non-planar)
b. planar, planar
c. bent (non-planar) , planar Incorrect. When oxygen concentration is high, the oxygen binds to iron
which pulls the iron and brings heme into a planar position. When oxygen is low, the iron is
deoxygenated and the heme is then bent.
d. planar, bent (non-planar)
The Bohr effect is a relationship between hemoglobin's oxygen binding behavior in conjunction with the
pH of the surroundings. When the pH is low, hemoglobin has _____________ affinity for oxygen and
________ oxygen.
Select one:
a. low, releases
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b. low, binds
c. high, releases
d. high, binds Incorrect. Low pH induces the T state which decreases hemoglobin affinity for oxygen;
hemoglobin releases oxygen .
Bohr effect is a relationship between hemoglobin's oxygen binding behavior in conjunction with the pH
of the surroundings. When the pH is high, hemoglobin has _____________ affinity for oxygen and
________ oxygen.
Select one:
a. low, binds
b. high, releases
c. high, binds
d. low, releases Incorrect. High pH induces the R state which increases hemoglobin's affinity for oxygen
so oxygen would remain bound.
Relative to the lungs, the pH in the peripheral tissues is _______ because __________________.
Select one:
a. lower, the CO2 generated by metabolism is converted to bicarbonate, which releases protons
(H+).
b. higher, the concentration of CO2 decreases. Incorrect. The pH of the tissue is lower than in the lungs
because the concentration of CO2 increases. This CO2 is converted to bicarbonate by the enzyme
carbonic anhydrase. Bicarbonate releases H+ which causes the pH to decrease.
c. lower, the concentration of oxygen decreases.
d. lower, carbonic anhydrase sequesters protons (H+).
The Bohr effect is a relationship between hemoglobin's oxygen binding behavior in conjunction with the
pH of the surroundings. When the H+ ion concentration increases, the pH of the solution
_________________.
Select one:
a. decreases
b.changes only if the oxygen concentration increases
c. increases Incorrect. pH is a measure of H+ ion concentration. Since the number calculated for pH is the
d. negative of a base 10 logarithm, the more H+ ions present in solution, the lower the pH.
does not change
Myoglobin stores oxygen, whereas hemoglobin transports oxygen. Which one of the following statements
is true?
Select one:
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a. Myoglobin has a higher affinity for oxygen compared to hemoglobin Correct! At lower oxygen
concentrations, a much higher fraction of myoglobin would be saturated with oxygen compared to
hemoglobin.
b. Hemoglobin and myoglobin both have the same affinity for oxygen
c. Hemoglobin has a higher affinity for oxygen compared to myoglobin
d. Myoglobin has exactly one-quarter of the affinity for oxygen because it has only one subunit
Hemoglobin is an oxygen transport protein, whereas myoglobin is an oxygen storage protein. They
exhibit different binding curves when plotted on a graph with total partial pressure of the oxygen (x-axis)
plotted against the percentage saturation of hemoglobin (y-axis). Which pattern of binding curves do
these proteins exhibit?
Select one:
a. Myoglobin has a sigmoidal curve whereas the hemoglobin has a hyperbolic curve
b. Both have a sigmoidal binding curve
c. Hemoglobin has a sigmoidal curve whereas the myoglobin has a hyperbolic curve Correct!
Myoglobin has a much higher affinity for oxygen with percent saturation increasing rapidly in low
oxygen concentrations; this is demonstrated by a hyperbolic curve. Hemoglobin initially binds to oxygen
at a slower rate at low oxygen concentrations, demonstrated by a sigmoidal curve.
d. Both have a hyperbolic binding curve
Hemoglobin and myoglobin proteins bind to molecular oxygen. However, the protein part of the
hemoglobin does not bind directly to the oxygen. Instead, a specific atom helps bind the oxygen. Which
one of the following will help hemoglobin directly bind to the oxygen?
Select one:
a. Heme
b. Iron Correct! Iron is the atom that binds directly with oxygen.
c. Carbon monoxide
d. Histidine
The symptoms of sickle cell anemia are primarily because red blood cells are misshaped. This is due to
____.
Select one:
a. a mutation in the alpha hemoglobin gene which leads to the insertion of valine into the hydrophobic
patches on oxygenated hemoglobin.
b. a mutation in the beta hemoglobin gene which leads to the insertion of valine into the
hydrophobic patches on deoxygenated hemoglobin.
c. a mutation in the beta hemoglobin gene which leads to insertion of glutamate into the hydrophobic
patches on oxygenated hemoglobin. Incorrect.Glutamate is a charged amino acid; its R group will not
interact with a hydrophobic pocket.
d. a mutation in the alpha hemoglobin gene which leads to the insertion of valine into the hydrophobic
patches on deoxygenated hemoglobin.
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Relative to the peripheral tissues, the pH in the lungs is _______ because __________________.
Select one:
a. higher, the protons (H+) that were combined with hemoglobin quickly bind to bicarbonate
(HCO3-) to form CO2; the CO2 is then exhaled.
b. higher, there is more oxygen in the lungs
c. lower, there is more CO2 present.
d. lower, the protons (H+) that were combined with hemoglobin quickly bind to bicarbonate (HCO3-) to
form CO2; the CO2 is then exhaled. Incorrect. Relative to the tissues, the lung tissue has a higher pH
because there are fewer protons (H+) in solution.
Carbon monoxide is poisonous because
Select one:
a. it binds hemoglobin 20 times less than oxygen.
b. it binds hemoglobin 200 times better than oxygen. Correct! Carbon monoxide has an affinity for
hemoglobin that is 200 times stronger than that of oxygen.
c. it binds hemoglobin 200 times less than oxygen.
d. None of the options are correct.
2,3 BPG stabilizes the _____ state(s) of hemoglobin.
Select one:
a. R
b. R and T
c. T Correct! 2,3 BPG stabilizes the T state of hemoglobin. This reduces hemoglobin's affinity for O2 and
promotes O2 release to the tissues, in much the same way as low pH.
d. None of the options are correct
Even though the amino acid sequence between subunits of hemoglobin and myoglobin are not exactly the
same, there are other similarities between the two proteins. Which level of protein structure is not found
in both molecules?
Select one:
a. Tertiary
b. Quaternary Correct! Myoglobin consists of a single subunit, while hemoglobin has four. Myoglobin
has primary, secondary, and tertiary levels of protein structure, however, it does not have a quaternary
structure. Any protein composed of only one subunit does not have quaternary structure.
c. Primary
d. Secondary
In the deoxygenated state the heme is ____________, where as in the oxygenated state, the heme is
_____________________.
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Select one:
a. planar, planar
b. bent (non-planar), planar
c. planar, bent (non-planar) Incorrect. In the deoxygenated state the heme is bent (non-planar), where as in
the oxygenated state, the heme is planar. When oxygen binds, the iron is pulled toward the oxygen the the
heme flattens to the planar shape. In the absence of oxygen, the histidine residue that binds to the Fe atom
will pull on the Fe and distort, or slightly bend, the heme plane.
d. bent (non-planar), bent (non-planar)
Fetal hemoglobin _____.
Select one:
a. is never in the R state.
b. has the exact same polypeptide chains as adult hemoglobin.
c. binds to oxygen tightly at lower oxygen concentrations since its R state is the preferred structure.
Correct! Fetal hemoglobin binds oxygen tightly at lower oxygen concentrations since its R state is the
preferred structure.
d. exhibits an oxygen binding curve that is the same shape as myoglobin oxygen binding curve
When the blood pH is low, the heme is in_______________ shape. When the blood pH is high, the heme
is in ______________shape.
Select one:
a. planar, bent (non-planar) Incorrect. When the blood pH is low, the heme is in bent (non-planar) shape
because hemoglobin has been deoxygenated. The T state of hemoglobin is favored by low pH and induces
the release of oxygen, while the R state is favored by higher pH and stimulates hemoglobin to bind more
O2 by increasing its affinity for oxygen.
b. planar, planar
c. bent (non-planar), planar
d. bent (non-planar), bent (non-planar)
In which of the following patients is the planar conformation of the heme group in hemoglobin favored?
Select one:
a. In a firefighter who is brought to the emergency room after entering a burning building Correct!
The oxygen concentration is higher in the emergency room than in the burning building. This would favor
the R state of the hemoglobin protein, and planar conformation of the heme group.
b. In an older woman with pneumonia and sepsis who has a blood pH of 7.1
c. In a girl with diabetic ketoacidosis
d. In the muscle capillaries of a patient who is on a treadmill for a cardiac stress test
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