mcq in heamoglobin & myoglobin

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moglobin & myoblobin

1. Which ligand increases the affinity of hemoglobin
for O2?

a. BGP
b. CO2
c. O2
d. H+
e. H2O
Ans:C
2. The effect of H+ on hemoglobin (Bohr effect) is to

a.
stabilize the oxy form.
b.
stabilize the deoxy form.
c.
destabilize the deoxy form.
d.
enhance the oxidation of the Fe2+.
e.
sterically block the O2 binding sites
Ans:bB
3. Sickle cell disease most likely results from an
increase in the

a.
ionic interactions between the hemoglobin molecules.
b.
hydrophobic interactions between the hemoglobin molecules.
c.
oxygen affinity of the hemoglobin molecule.
d.
molecular weight of the hemoglobin molecule.
e.
synthesis of hemoglobin.

Ans:B
4. In myoglobin and hemoglobin, oxygen binds directly
to

a. Fe2+
in the heme.
b. Fe3+
in the heme.
c. the
proximal histidine.
d. the
distal histidine.
e.
protoporphyrin IX.
Ans:A
5. All of the following statements about myoglobin
structure are correct EXCEPT:

a.
Myoglobin has a high a-helical content.
b. Most
of the charged residues are located on the inside of the molecule.
c. The
interior part of the molecule contains mainly the non-polar amino acids.

d.
Proline terminates some of the a-helical regions.
e.
Myoglobin contains a single polypeptide chain.
Ans:B

6. Which of the following increases hemoglobin's
oxygen binding?

a. A
decrease in pH
b. An
increase in BPG level
c. An
increase in CO2 level
d.
Binding of oxygen at one or more heme sites
e. A
decrease in the partial pressure of oxygen
Ans:dD
7. Comparing the oxygen dissociation curves of
hemoglobin and myoglobin, which of the following is correct:

a. In
the lung, much less oxygen is loaded to hemoglobin than to myoglobin.
b.
Myoglobin and hemoglobin unload the same amount of oxygen in response to
a small decrease in oxygen partial pressure.
c.
Myoglobin unloads more oxygen in response to a small decrease in oxygen
partial pressure.
d.
Hemoglobin unloads more oxygen in response to a small decrease in oxygen
partial pressure.
e.
Hemoglobin has a higher oxygen affinity than myoglobin.
Ans:D
8. Sickle cell anemia is caused by a mutation in
hemoglobin that causes:

a. a
change from a non-charged amino acid to a charged amino acid.
b. a
change from a charged amino acid to a hydrophobic amino acid.
c. loss
of a post-translational modification of an amino acid.
d. a
failure to reduce Fe3+ to Fe2+.
e.
dissociation of hemoglobin to dimers.
Ans:B
9. The concentration of 2,3-bisphosphoglycerate (BPG)
in human erythocytes increases by 50 percent within 2 days upon
reaching an altitude of 4000m. How is hemoglobin (Hb) affected by this
increase in BPG?

a.
Oxygen binding increases due to heterotropic allosteric interactions.
b.
Oxygen binding increases due to homotropic allosteric interactions.
c. Hb
has a greater tendency to polymerize.
d. Less
carbon dioxide is bound to the alpha chain amino groups of Hb.
e. The
relative amount of deoxy Hb increases.
Ans:E
10. How does fetal hemoglobin (Hb F) differ from
normal adult hemoglobin (Hb A)?

a. A
histidine residue in Hb A is replaced with a neutral amino acid in Hb F.
b. An
alpha chain lysine residue in Hb A is replaced with a neutral amino acid
in Hb F.
c. Hb F
has a greater tendency to associate in the deoxygenated state.
d. Hb F
has a greater affinity for CO.
e. Hb F
exhibits enhanced oxygen unloading versus Hb A at the same pO2
Ans:A
11. What are the differences between the quaternary
structural characteristics of deoxyhemoglobin (deoxy-Hb) versus
oxyhemoglobin (oxy-Hb)?

a.
Oxy-Hb has a less compact structure than deoxy-Hb.
b.
Deoxy-Hb has a smaller central cavity than oxy-Hb.
c.
Deoxy-Hb subunit contacts are oriented differently than oxy-Hb.
d.
Oxy-Hb has the same but more condensed subunit contacts as deoxy-Hb.
e.
Deoxy-Hb has a greater tendency to aggregate than oxy-Hb
Ans:C
12. The O2 binding affinity of hemoglobin decreases
when there is a decrease in

a.
ionic strength.
b.
2,3-bisphosphoglycerate concentration.
c.
carbon dioxide concentration.
d. pH.
Ans:D
13. Allosteric interactions in hemoglobin (Hb) cause
O2 to bind

a. to
all four heme groups of Hb with the same binding affinity.
b. with
increasing affinity as the number of heme groups with O2 already bound increases.
c. with
decreasing affinity as the number of heme groups with O2 already bound increases.
d. to
one subunit of all molecules before binding to the second heme subunit.
e. to
beta subunits prior to binding to alpha subunits.
Ans:B
14. What is the important difference between
hemoglobin (Hb) and myoglobin (Mb)?

a. Hb
is a heterotetramer containing 2 alpha and 2 beta chains.
b. Hb
binds oxygen more tightly than Mb.
c. Each
chain in Hb contains a heme prosthetic group.
d. Hb
does not bind CO.
e. The
polypeptide chains of Hb are folded mostly into alpha-helices.
Ans:A
15. How does sickle cell hemoglobin (Hb S) differ
from normal adult hemoglobin (Hb A)?

a. Hb S
shows a reduced affinity for carbon dioxide.
b. Hb S
shows a reduced ability to bind oxygen at the same pO2
c. Hb S
binds BPG more avidly.
d. Hb S
tends to polymerize in the deoxy-form.
e. Hb S
shows a loss of allosteric effects.
Ans:D
16. The increased metabolic activity that occurs in
muscle tissue during exercise causes hemoglobin to release more oxygen
to the tissue for all of the following reasons EXCEPT:

a.Muscle
produces higher levels of H+.
b.Muscle
produces higher levels of CO2.
c.The
partial pressure of oxygen in the muscle is reduced.
d. BPG
dissociates from hemoglobin.
Ans:D

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