Hemoglobin and Myoglobin Structure and Function
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Questions and Answers

What is the quaternary structure of Hb?

  • A trimer of alpha, beta, and gamma globin subunits
  • A monomer
  • A tetramer of alpha and beta globin subunits
  • A dimer of a dimer (α1β1)(α2β2) (correct)

    • What is the approximate number of amino acids in the globin subunits?

  • 200
  • 100
  • 250
  • 150 (correct)

    • How do the haem groups bind oxygen?

  • Through the hydrophobic pocket
  • Through the alpha helices
  • Through the hydrophilic side of the haem group (correct)
  • Through the beta globin subunits

    • What is the difference between Hb and Mb?

    <p>Hb is a tetramer, while Mb is a monomer</p> Signup and view all the answers

    What is the structure of the globin subunits?

    <p>Consisting of alpha helices</p> Signup and view all the answers

    What is the location of the haem group within the globin?

    <p>Buried within a hydrophobic pocket</p> Signup and view all the answers

    What is the primary effect of allosteric binding of oxygen to one globin subunit?

    <p>Increase in the affinity of the other globin subunits for oxygen</p> Signup and view all the answers

    In which conformational state does the globin subunit have a high affinity for oxygen?

    <p>R (relaxed) conformation</p> Signup and view all the answers

    What is the effect of binding of oxygen to the α1 subunit on the β1 subunit?

    <p>Changes the conformation of β1 to R state</p> Signup and view all the answers

    What is the primary reason for cooperative binding of oxygen to hemoglobin in the lungs?

    <p>Allosteric binding of oxygen to Hb in the lungs</p> Signup and view all the answers

    What is the effect of increased site occupancy of Hb on its affinity for oxygen?

    <p>Increases its affinity for oxygen</p> Signup and view all the answers

    What is the primary consequence of the conformational change in the globin subunit upon binding of oxygen?

    <p>Increase in the affinity of the subunit for oxygen</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 primary mechanism by which carbon dioxide is converted to bicarbonate in erythrocytes?

    <p>Carbonic anhydrase</p> Signup and view all the answers

    What is the effect of increasing [H+] on the ability of haemoglobin to bind oxygen?

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

    What is the primary function of the Cl-/HCO3- channel in erythrocytes?

    <p>To export bicarbonate</p> Signup and view all the answers

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

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

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

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

    What is the primary product of the reaction between carbon dioxide and water in erythrocytes?

    <p>Carbonic acid</p> Signup and view all the answers

    What is the significance of the Bohr effect in peripheral tissues?

    <p>It allows for complete desaturation of haemoglobin</p> Signup and view all the answers

    What is the primary reason for the conformation change in deoxyHbS?

    <p>To prevent the valine from being in an aqueous environment</p> Signup and view all the answers

    What is the consequence of polymers of HbS on the erythrocyte membrane?

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

    What is the result 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 production of α-globin chains</p> Signup and view all the answers

    What is the name of the haemoglobin formed in α-thalassaemia in adults?

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

    What is the consequence of sickle-shaped cells in capillaries?

    <p>Trapping and lysis of sickle-shaped cells</p> Signup and view all the answers

    What is the primary reason behind monitoring haemoglobin levels in individuals with type 1 diabetes?

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

    What is the consequence of glucose reacting with plasma proteins in diabetic individuals?

    <p>Non-enzymatic glycosylation of proteins</p> Signup and view all the answers

    What is the characteristic of haemoglobin that makes it suitable for monitoring glucose levels?

    <p>Its long half-life of 120 days</p> Signup and view all the answers

    What is the genetic basis of sickle cell anaemia?

    <p>Recessively inherited mutation of β-globin</p> Signup and view all the answers

    What is the effect of the glutamic acid to valine substitution in sickle cell anaemia?

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

    What is the characteristic of haemoglobin in sickle cell anaemia?

    <p>HbS is a less efficient oxygen carrier than normal HbA</p> Signup and view all the answers

    What is the difference between sickle cell disease and sickle cell trait?

    <p>Sickle cell disease is caused by two copies of the mutant gene, while sickle cell trait is caused by one copy of the mutant gene</p> Signup and view all the answers

    What is the consequence of the formation of sickle-shaped cells in sickle cell anaemia?

    <p>Increased risk of blood clots and vascular occlusion</p> Signup and view all the answers

    Study Notes

    Structure of Hemoglobin and Myoglobin

    • Hemoglobin (Hb) is a tetramer, consisting of 2 identical beta globin subunits and 2 identical alpha globin subunits.
    • Hb is a dimer of a dimer, with the structure (α1β1)(α2β2).
    • In adults, Hb is primarily HbA.
    • Myoglobin (Mb) is a monomer.
    • Mb and Hb have similar structures, consisting of alpha helices and a hydrophobic pocket containing a haem group.

    Binding of Oxygen to Hemoglobin

    • Each haem group can bind oxygen.
    • Allostery occurs when the binding of oxygen to one globin changes the shape of the binding site of another globin.
    • The affinity of Hb for oxygen increases as the site occupancy increases.
    • When pO2 is high (in the lungs), cooperative binding allows Hb to be fully saturated.

    Tense and Relaxed Forms of Hemoglobin

    • Each globin subunit can exist in two forms: T (tense) conformation with low affinity for oxygen and R (relaxed) conformation with high affinity for oxygen.
    • Binding of oxygen to one subunit causes a conformational change in the subunit, leading to a conformational change of a second subunit to the R state.
    • For example, binding of oxygen to α1 changes the conformation of α1, which in turn changes β1 to the R state, increasing its affinity for oxygen.

    Transportation of Carbon Dioxide in Blood

    • A small amount of carbon dioxide is dissolved in blood plasma.
    • Carbon dioxide freely crosses the erythrocyte plasma membrane.
    • Most carbon dioxide is converted to carbonic acid by carbonic anhydrase in erythrocytes.
    • Carbonic acid dissociates to bicarbonate, which is exported via the Cl-/HCO3- channel.
    • Some carbon dioxide reversibly binds to Hb to form carbaminohaemoglobin.

    Bohr Effect

    • The ability of Hb to bind oxygen decreases as the [H+] increases.
    • The ability of Hb to bind oxygen decreases as the pH decreases.
    • This is a physiologically important biological adaptation, allowing Hb to release more oxygen in peripheral tissues.

    Impact of [H+] on Oxygen Binding of Hemoglobin in the Periphery

    • In peripheral tissues, Hb releases more oxygen due to the increased [H+] resulting from carbon dioxide production.
    • This is important for the delivery of oxygen to tissues.

    Type 1 Diabetes and Hemoglobin

    • Hemoglobin is monitored in type 1 dependent diabetes because glucose can cause non-enzymatic glycosylation of plasma proteins.
    • Glycosylated Hb (HbA1c) is used to monitor glucose levels over a three-month period.

    Sickle Cell Anaemia

    • Sickle cell anaemia is a recessively inherited anaemia characterised by the formation of sickle-shaped cells.
    • It is caused by an inherited mutation of β-globin, resulting in the substitution of glutamic acid with valine at position 6.
    • This creates hydrophobic "sticky" patches on the normally charged surface of the β-globin.

    HbS Aggregation

    • A conformation change in deoxyHb results in the alpha helix containing position 6 shifting to the surface.
    • In HbS, the valine at position 6 is not stabilised by hydrogen bonds with the aqueous environment, leading to aggregation of two haemoglobins.
    • This aggregation continues to form polymers.

    Formation of Sickle-Shaped Cells

    • The polymers of HbS disrupt the erythrocyte membrane and prevent deformability, resulting in sickle-shaped cells.
    • These cells can be trapped in capillaries and lyse.

    Haemoglobin and Other Diseases

    • Low Fe2+ intake in the diet can lead to anaemia.
    • Hereditary haemolytic anaemia can result from an imbalance of globin chain production.
    • α-thalassaemia is characterised by deficient α-globin production, leading to excess β chains.
    • β-thalassaemia is characterised by deficient β-globin production.
    • Hereditary Persistence of Fetal Haemoglobin (HPFH) is a rare condition in which fetal haemoglobin is persistently produced in adults.

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    Description

    Learn about the structures of Hemoglobin and Myoglobin, including their subunits, binding of oxygen, and allosteric effects.

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