Biochemistry: Hemoglobin Structure
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Questions and Answers

What is the quaternary structure of hemoglobin in adults?

  • A dimer of two identical alpha globin subunits
  • A dimer of a dimer (α1β1)(α2β2) (correct)
  • A monomer of a single alpha globin subunit
  • A tetramer of four identical beta globin subunits

    • What is the main difference between the structure of myoglobin and hemoglobin?

  • Hemoglobin is a monomer, while myoglobin is a tetramer
  • Myoglobin has a haem group, while hemoglobin does not
  • Myoglobin has a higher oxygen affinity than hemoglobin
  • Hemoglobin has a dimer of a dimer structure, while myoglobin is a monomer (correct)

    • What is the function of the hydrophobic pocket in globins?

  • To facilitate the binding of carbon dioxide
  • To bind oxygen molecules
  • To bury the haem group (correct)
  • To increase the oxygen affinity of the globin

    • What is the orientation of the hydrophilic side of the haem group in globins?

    <p>It faces the surface of the globin</p> Signup and view all the answers

    What is the length of the globin proteins?

    <p>Approximately 150 amino acids</p> Signup and view all the answers

    What is the secondary structure of the globin proteins?

    <p>Alpha helices only</p> Signup and view all the answers

    What is the primary mechanism by which carbon dioxide is transported in the blood?

    <p>Conversion to bicarbonate by carbonic anhydrase</p> Signup and view all the answers

    What percentage of carbon dioxide is dissolved in blood plasma?

    <p>10%</p> Signup and view all the answers

    What is the effect of an increase in [H+] on the binding of oxygen to haemoglobin?

    <p>Decreases oxygen binding</p> Signup and view all the answers

    At what pH is the 50% Hb saturation at pO2 ~27 mm Hg?

    <p>7.4</p> Signup and view all the answers

    What is the primary function of carbonic anhydrase in erythrocytes?

    <p>Converting carbon dioxide to bicarbonate</p> Signup and view all the answers

    What is the physiological importance of the Bohr effect?

    <p>To decrease oxygen binding to haemoglobin in the periphery</p> Signup and view all the answers

    What is the result of an increase in [H+] in peripheral tissues?

    <p>Decreased oxygen binding to haemoglobin</p> Signup and view all the answers

    What is the percentage of carbon dioxide that is transported bound to haemoglobin?

    <p>30%</p> Signup and view all the answers

    Why is haemoglobin monitored in type 1 diabetes?

    <p>To monitor the level of glucose maintained over a period of time</p> Signup and view all the answers

    What is the consequence of non-enzymatic glycosylation of plasma proteins?

    <p>Rapid degradation of the proteins</p> Signup and view all the answers

    What is the half-life of haemoglobin?

    <p>120 days</p> Signup and view all the answers

    What is the substitution in sickle cell anaemia?

    <p>Glu 6 val</p> Signup and view all the answers

    What is the effect of the substitution in sickle cell anaemia?

    <p>Creates a hydrophobic patch on the surface of β-globin</p> Signup and view all the answers

    What is the term for individuals with one copy of the mutant gene?

    <p>Sickle cell trait</p> Signup and view all the answers

    What is the term for individuals with two copies of the mutant gene?

    <p>Sickle cell disease</p> Signup and view all the answers

    What is the shape of the cells in sickle cell anaemia?

    <p>Sickle-shaped</p> Signup and view all the answers

    What is the result of a reduced level of carbon dioxide in the blood?

    <p>pH increases and H+ decreases</p> Signup and view all the answers

    Which type of hemoglobin has a higher affinity for oxygen?

    <p>HbF</p> Signup and view all the answers

    What is the function of 2,3-bisphosphoglycerate (BPG) in oxygen binding of hemoglobin?

    <p>Decreases the affinity of Hb for oxygen</p> Signup and view all the answers

    What is the ratio of HbA to HbF at birth?

    <p>20% HbA - 80% HbF</p> Signup and view all the answers

    What is the effect of the Bohr effect on oxygen release to tissues in the periphery?

    <p>Increases oxygen release</p> Signup and view all the answers

    Which type of hemoglobin is saturated in preference to HbA in the placenta?

    <p>HbF</p> Signup and view all the answers

    What is the pO2 at which 50% of HbA is saturated?

    <p>27 mm Hg</p> Signup and view all the answers

    What is the effect of BPG binding on HbF?

    <p>Increases the difference in affinities between HbF and HbA</p> Signup and view all the answers

    What is the main consequence of the conformation change in deoxyHbS?

    <p>Disruption of the erythrocyte membrane</p> Signup and view all the answers

    What is the role of hydrogen bonds in sickle cell disease?

    <p>Stabilizing glutamic acid in HbA</p> Signup and view all the answers

    What is the result of polymers of HbS forming in the erythrocyte?

    <p>Disruption of the erythrocyte membrane and prevention of deformability</p> Signup and view all the answers

    What is the consequence of low Fe2+ intake in the diet?

    <p>Anaemia</p> Signup and view all the answers

    What is the characteristic of α-thalassaemia?

    <p>Deficient α-globin production</p> Signup and view all the answers

    What is the characteristic of HbH?

    <p>Tetramer of β-globin (β4)</p> Signup and view all the answers

    Study Notes

    Structure of Hemoglobin and Myoglobin

    • Hemoglobin (Hb) is a tetramer composed of 2 identical beta globin subunits and 2 identical alpha globin subunits
    • Hb is a dimer of a dimer (α1β1)(α2β2)
    • In adults, Hb is HbA
    • Myoglobin (Mb) is a monomer
    • Both Mb and Hb have similar structures with alpha helices and a haem group buried within a hydrophobic pocket

    Transportation of Carbon Dioxide in Blood

    • Carbon dioxide is transported in the blood through three mechanisms:
      • Dissolved in blood plasma (10%)
      • Converted to bicarbonate (60%)
      • Bound to Hb (30%)

    Bohr Effect

    • The ability of hemoglobin to bind oxygen decreases as the [H+] increases or as the pH decreases
    • This effect is physiologically important in peripheral tissues, where oxygen is released from hemoglobin in response to increased carbon dioxide levels

    Fetal Hemoglobin

    • During development, different hemoglobins are expressed, including embryonic hemoglobins and fetal hemoglobin (HbF)
    • HbF has a higher affinity for oxygen than HbA
    • At birth, 20% of hemoglobin is HbA and 80% is HbF

    2, 3-Bisphosphoglycerate (BPG) and Oxygen Binding

    • BPG is an allosteric regulator of oxygen binding of hemoglobin
    • BPG binds to the internal position of Hb but only in the T-state (deoxyHb)
    • BPG lowers the affinity of Hb for oxygen
    • HbF has a variation in sequence that reduces BPG binding, increasing the difference in affinities between HbF and HbA

    Type 1 Diabetes and Hemoglobin

    • Diabetes results in elevated plasma glucose levels, which can cause non-enzymatic glycosylation of plasma proteins
    • Hemoglobin is not degraded after synthesis and has a half-life of 120 days
    • The level of glycosylated Hb (HbA1c) is used to monitor glucose levels over a three-month period

    Sickle Cell Anemia

    • Sickle cell anemia is a recessively inherited anemia characterized by the formation of sickle-shaped cells
    • The disease is caused by an inherited mutation of β-globin, resulting in a substitution of glutamic acid with valine at position 6
    • This substitution creates hydrophobic "sticky" patches on the surface of the β-globin
    • The sickle cell trait is characterized by one copy of the mutant gene, while sickle cell disease is characterized by two copies of the mutant gene

    HbS Aggregation

    • Conformation change in deoxyHb results in the alpha helix containing position 6 shifting to the surface
    • In HbA, glutamic acid is stabilized by hydrogen bonds with the aqueous environment
    • In HbS, the valine is not in an aqueous environment, leading to aggregation of two hemoglobins
    • This aggregation continues to form polymers

    Formation of Sickle-Shaped Cells

    • Polymers of HbS disrupt the erythrocyte membrane and prevent deformability, resulting in sickle-shaped cells
    • Sickle-shaped cells can be trapped in capillaries and lyse

    Hemoglobin and Other Diseases

    • Low Fe2+ intake in diet may lead to anemia
    • Hereditary hemolytic anemia can be caused by an imbalance of globin chain production
    • α-thalassaemia is characterized by deficient α-globin production, while β-thalassaemia is characterized by deficient β-globin production
    • Hereditary persistence of fetal hemoglobin (HPFH) is a condition where HbF is produced throughout adulthood

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    Description

    This quiz covers the structure of hemoglobin (Hb) and myoglobin (Mb), including their subunits and biochemical composition.

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