Hemoglobin and Myoglobin Structure and Function

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?

Hb is a tetramer, while Mb is a monomer Signup and view all the answers

What is the structure of the globin subunits?

Consisting of alpha helices Signup and view all the answers

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

Buried within a hydrophobic pocket Signup and view all the answers

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

Increase in the affinity of the other globin subunits for oxygen Signup and view all the answers

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

R (relaxed) conformation Signup and view all the answers

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

Changes the conformation of β1 to R state Signup and view all the answers

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

Allosteric binding of oxygen to Hb in the lungs Signup and view all the answers

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

Increases its affinity for oxygen Signup and view all the answers

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

Increase in the affinity of the subunit for oxygen Signup and view all the answers

What percentage of carbon dioxide is dissolved in blood plasma?

10 Signup and view all the answers

What is the primary mechanism by which carbon dioxide is converted to bicarbonate in erythrocytes?

Carbonic anhydrase Signup and view all the answers

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

Decreases the binding of oxygen Signup and view all the answers

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

To export bicarbonate Signup and view all the answers

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

30 Signup and view all the answers

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

Decrease in oxygen binding to haemoglobin Signup and view all the answers

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

Carbonic acid Signup and view all the answers

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

It allows for complete desaturation of haemoglobin Signup and view all the answers

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

To prevent the valine from being in an aqueous environment Signup and view all the answers

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

Disruption of the erythrocyte membrane Signup and view all the answers

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

Anaemia Signup and view all the answers

What is the characteristic of α-thalassaemia?

Deficient production of α-globin chains Signup and view all the answers

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

HbH Signup and view all the answers

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

Trapping and lysis of sickle-shaped cells Signup and view all the answers

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

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

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

Non-enzymatic glycosylation of proteins Signup and view all the answers

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

Its long half-life of 120 days Signup and view all the answers

What is the genetic basis of sickle cell anaemia?

Recessively inherited mutation of β-globin Signup and view all the answers

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

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

What is the characteristic of haemoglobin in sickle cell anaemia?

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

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

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 Signup and view all the answers

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

Increased risk of blood clots and vascular occlusion 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.