Deck 7: Hemoglobin: a Portrait of a Protein in Action

Question 1

The ability of myoglobin to bind oxygen depends on the presence of a bound prosthetic group called _____________.

Answer 1

heme

Question 2

What is the organic portion of the heme group in hemoglobin?

A) protoporphyrinogen
B) protoporphyrin
C) uroporphyrinogen
D) coproporphyrinogen
E) protoheme

Answer 2

B

Question 3

The binding of 2-3-bisphosphogycerate to hemoglobin ____________ (increases, decreases) its affinity of oxygen binding.

Answer 3

decreases

Question 4

Which of the following is the immediate product of the reaction between carbon dioxide and water?

A) HCO₂H
B) HCO₃^-
C) CO₃^2-
D) H₂CO₃^-
E) None of the answers is correct.

Question 5

In normal adult hemoglobin, HbA, the β6 position is a glutamate residue, whereas in sickle-cell hemoglobin, HbS, it is a ____________ residue.

Question 6

In hemoglobin, the iron of the heme is bonded to the four nitrogens of porphyrin and to the proximal ______________ residue of the globin chain.

Question 7

What type of binding is indicated by a sigmoidal-shaped binding curve?

A) competitive
B) noncompetitive
C) uncooperative
D) cooperative
E) None of the answers is correct.

Question 8

What oxidized heme protein does not reversibly bind oxygen?

A) metmyoglobin
B) oxyhemoglobin
C) carboxyhemoglobin
D) leghemoglobin
E) None of the answers is correct.

Question 9

What is the composition of fetal hemoglobin?

A) two $\alpha$ chains and two $\beta$ chains
B) two $\alpha$ chains and two $\gamma$ chains
C) two $\gamma$ chains and two $\beta$ chains
D) two $\alpha$ chains and two $\delta$ chains
E) four $\beta$ chains

Question 10

What is formed when carbon dioxide reacts with the amino terminal group of deoxyhemoglobin?

A) amide
B) imine
C) carbonate
D) carbamate
E) None of the answers is correct.

Question 11

Another reason why hemoglobin is sensitive to changes in pH is that the T-state of hemoglobin is stabilized by a salt bridge between β₁ Asp 94 and the C-terminal ___________________ of the β1 chain.

Question 12

Which of the following represents the most predominant form for the transfer of carbon dioxide in the blood?

A) CO₂
B) H₂CO₃
C) HCO₃^-
D) CO₃^2-
E) None of the answers is correct.

Question 13

Under normal conditions, the heme iron in myoglobin and hemoglobin is in the ____________ oxidation state.

Question 14

What condition results from a single point mutation of the hemoglobin $\beta$ chain, producing the HbS variant?

A) $\alpha$ -thalassemia
B) $\beta$ -thalassemia
C) hemoglobin SC disease
D) hemolytic anemia
E) sickle-cell anemia

Question 15

Which of the following is a genetic disease that results from a decreased production of one of the subunits of hemoglobin?

A) thalassemia
B) pernicious anemia
C) megaloblastic hereditary anemia
D) acanthocytosis
E) aplastic anemia

Question 16

What factor(s) influence(s) the binding of oxygen to myoglobin?

A) the concentration of bicarbonate ion, HCO₃^-
B) the partial pressure of oxygen, pO₂
C) the concentration of hemoglobin present
D) the concentration of 2,3-BPG
E) both the partial pressure of oxygen, pO₂and the concentration of 2,3-BPG

Question 17

What molecule stores oxygen in muscle cells?

A) individual $\alpha$ subunits of hemoglobin
B) individual $\beta$ subunits of hemoglobin
C) myoglobin
D) metmyoglobin
E) carboxyhemoglobin

Question 18

The effect of pH on oxygen-binding of hemoglobin is referred to as the _____________.

Question 19

As the partial pressure of carbon dioxide increases, the affinity of oxygen binding to hemoglobin ______________.

Question 20

The T-state structure of deoxyhemoglobin is stabilized through ___________________ interactions between the carbamates and positively charged amino acids at the interface between αβ dimers.

Question 21

Carbon dioxide forms carbamate groups in proteins by reaction with

A) aspartate residues.
B) cysteine residues.
C) N-terminal amino groups.
D) tyrosine residues.
E) heme groups.

Question 22

The structure of normal adult hemoglobin can be described as a tetramer composed of

A) four myoglobin molecules.
B) two αβ dimers.
C) two α₂ and two β₂ dimers.
D) two α₂ and two γ₂ dimers.
E) None of these accurately describe hemoglobin.

Question 23

Which of the following describes the Bohr effect?

A) Lowering the pH results in the release of O₂ from oxyhemoglobin.
B) Increasing the concentration of HCO₃^- results in the release of O₂ from oxyhemoglobin.
C) Increasing the pH increases the prevalence of the T-form of hemoglobin.
D) All of the answers are correct.
E) Lowering the pH and increasing the concentration of HCO₃^- results in the release of O₂ from oxyhemoglobin .

Question 24

Which of the following is correct concerning the differences between hemoglobin and myoglobin?

A) Both hemoglobin and myoglobin are tetrameric proteins.
B) Hemoglobin exhibits a hyperbolic O₂ saturation curve while myoglobin exhibits a sigmoid shaped curve.
C) Hemoglobin exhibits cooperative binding of O₂ while myoglobin does not.
D) Hemoglobin exhibits a higher degree of O₂ saturation at all physiologically relevant partial pressures of O₂ than does myoglobin.
E) All of the answers are correct.

Question 25

Which of the following is correct concerning the oxygenation plot of proteins X and Y shown below?

A) Protein Y exhibits tighter oxygen binding than protein X.
B) Protein Y would function as a better oxygen-transport protein than protein X.
C) Protein X exhibits cooperative binding, whereas Y does not.
D) Protein Y corresponds to myoglobin, and protein X corresponds to hemoglobin.
E) Protein X contains multiple binding sites.

Question 26

Consider the oxygen-binding profile at three different pH values of 7.6, 7.4, and 7.2. Which statement is most correct?

A) Curve X most likely corresponds to pH 7.2.
B) Curve Z most likely corresponds to pH 7.6.
C) Hb has a higher affinity for oxygen at the pH of curve Z.
D) Curve Y most likely corresponds to pH 7.4.
E) pH has no effect on the oxygenation of hemoglobin.

Question 27

What is the Bohr effect?

A) the ability of hemoglobin to retain oxygen when in competition with myoglobin
B) the regulation of hemoglobin-binding by hydrogen ions and carbon dioxide
C) the alteration of hemoglobin conformation during low oxygen stress
D) All of the answers are correct.
E) None of the answers is correct.

Question 28

Which of the following is NOT correct concerning myoglobin?

A) The globin chain contains an extensive α-helix structure.
B) The heme group is bound to the globin chain by two disulfide bonds to cysteine residues.
C) The iron of the heme group is in the Fe²⁺ oxidation state.
D) The diameter of the iron ion decreases upon binding to oxygen.
E) The function of myoglobin is oxygen storage in muscle.

Question 29

Hemoglobin-binding of oxygen is best described as a

A) concerted model.
B) Michaelis-Menten model.
C) sequential model.
D) combination of sequential and concerted models.
E) None of the answers is correct.

Question 30

Which of the following is correct concerning fetal hemoglobin?

A) Fetal hemoglobin is composed of two α and two γ subunits.
B) Fetal hemoglobin binds 2,3-BPG more tightly than normal adult hemoglobin.
C) Fetal hemoglobin binds oxygen less than HbA at all pO₂.
D) Fetal hemoglobin does not exist in the T-form.
E) None of the answers is correct.

Question 31

Sickle-cell anemia is caused by

A) a decreased production of α chains of hemoglobin.
B) a substitution of a Glu residue for a Phe residue at the β6 position.
C) the loss of the heme group because the proximal His is oxidized.
D) a substitution of a Val residue for a Glu residue at the β6 position.
E) a substitution of Glu residue for His at the C-terminal of the α chain.

Question 32

2,3-bisphosphoglycerate

A) binds in the central cavity in the T-form of hemoglobin.
B) preferentially binds to oxyhemoglobin and stabilizes it.
C) binds to positively charged groups on the $\beta$ subunits.
D) All of the answers are correct.
E) binds in the central cavity in the T-form of hemoglobin and binds to positively charged groups on the $\beta$ subunits.

Question 33

Which of the following is correct concerning the following equilibrium? CO₂ + H₂O H₂CO₃

A) An increase in the pressure of CO₂ will result in a decrease of pH.
B) This reaction is catalyzed by carbonic anhydrase.
C) The H₂CO₃ dissociates to H⁺ and bicarbonate ion, HCO₃^-.
D) The majority of CO₂ is transported to the lungs in the form of HCO₃^-.
E) All of the answers are correct.

Question 34

Why is the HbS mutation so prevalent in Africa and other tropical regions?

A) The oxygen binds with greater affinity to the proximal histidine residue of HbS.
B) Bonding of carbon dioxide to HbS molecules increases the binding of oxygen.
C) Hemoglobin binds more oxygen with the reduction of the hemoglobin S chain.
D) Hemoglobin binds more oxygen with aggregations of α chains found in sickle-cell hemoglobin.
E) People with sickle-cell trait are resistant to malaria, increasing the prevalence of the HbS allele.

Question 35

Which of the following is correct concerning the oxygenation plot of proteins X and Y shown below?

A) Protein Y exhibits tighter oxygen-binding than protein X.
B) Protein Y corresponds to fetal hemoglobin, and protein X corresponds to normal adult hemoglobin.
C) Protein X corresponds to fetal hemoglobin, and protein Y corresponds to normal adult hemoglobin.
D) Protein X corresponds to myoglobin, and protein Y corresponds to hemoglobin.
E) None of the answers is correct.

Question 36

Which is NOT correct concerning the accepted models that describe cooperative binding?

A) In the sequential model, the binding of a ligand changes the conformation of the subunit to which it binds, in turn inducing a change in neighboring subunits.
B) All known allosteric proteins exhibit either the concerted or sequential model exclusive of the other.
C) Both models incorporate a low affinity T-state and a higher affinity R-state.
D) Both models explain the sigmoid-shaped binding curve.
E) In the concerted model, all molecules exist either in the T-state or the R-state.

Question 37

What is metmyoglobin?

Question 38

What is fetal hemoglobin? How does it differ from adult hemoglobin?

Question 39

What would be the expected result of a Lys residue being replaced by a Ser residue in the BPG binding site of hemoglobin?

A) BPG would bind tighter because of the loss of a positive charge.
B) BPG would bind tighter because of the gain of a positive charge.
C) BPG would bind less tightly because of the loss of a positive charge
D) BPG would bind less tightly because of the gain of a positive charge.
E) This substitution would have no effect on the binding of BPG.

Question 40

Why is it advantageous for hemoglobin to have allosteric properties?

Question 41

Draw the oxygen-binding curve of myoglobin and that of hemoglobin. Indicate the partial pressure of oxygen in the lungs and the range of pressure in tissue.

Question 42

Briefly describe the cause of sickle-cell anemia.

Question 43

What is thalassemia?

Question 44

Describe how carbon dioxide affects the oxygenation of hemoglobin.

Question 45

Describe the structure of normal adult hemoglobin.

Question 46

Describe the chemical basis of the Bohr effect.

Question 47

Describe the recurring structure called the globin fold.

Question 48

What functional role does the "distal histidine" play in the function of myoglobin and hemoglobin?

Question 49

What is neuroglobin, and what is its suspected role?

Question 50

Describe the role of 2,3-bisphosphoglycerate in the function of hemoglobin.

Question 51

What is the role of α-hemoglobin stabilizing protein?

Question 52

Describe the concerted model to explain allosteric cooperative binding.