Haemoglobin Structure and Function

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Questions and Answers

What is the structure of a haemoglobin molecule?

Six polypeptide chains, each bound to two haem groups

Two polypeptide chains and one haem group

Four polypeptide chains, each bound to a haem group (correct)

Four polypeptide chains and a single haem group

How many binding sites does the iron atom in haemoglobin have?

5 binding sites

6 binding sites (correct)

4 binding sites

7 binding sites

Which statement best describes the concept of co-operative binding in haemoglobin?

Haemoglobin can only bind oxygen when it is not bound to carbon dioxide

The binding of one oxygen molecule increases the affinity of haemoglobin for additional oxygen molecules (correct)

One oxygen molecule binds and reduces the affinity for more oxygen

All haemoglobin molecules bind oxygen at the same time without any interaction

What role does iron play in the haemoglobin structure?

It facilitates the binding of oxygen Signup and view all the answers

What are the components bound to each haem group in haemoglobin?

Iron atoms Signup and view all the answers

What is considered a normal haemoglobin level for women according to the World Health Organization?

12 g/dl Signup and view all the answers

What type of haemoglobinopathy is caused by absent or decreased production of globin chains?

Alpha or beta thalassemia Signup and view all the answers

Which of the following symptoms is commonly associated with sickle cell disease when experiencing a sickling event?

Intense pain Signup and view all the answers

How does haemoglobin S differ from normal haemoglobin?

It has abnormal beta chains due to a single amino acid substitution Signup and view all the answers

What is a potential genetic advantage conferred by the sickle cell trait?

Resistance against malaria Signup and view all the answers

What can cause the red blood cells in sickle cell disease to obstruct blood flow?

Shape distortion of the cells due to low oxygen Signup and view all the answers

What laboratory finding is below the normal reference range for mean corpuscular volume (MCV) in the case presented?

56.2 fL Signup and view all the answers

What is the role of haemoglobin in oxygen transport?

It binds to oxygen and transports it from the lungs to tissues. Signup and view all the answers

What is the oxygen saturation of normal arterial blood?

95 - 100% Signup and view all the answers

Which statement about the binding of oxygen to haemoglobin is true?

The fourth O2 has a significantly higher affinity than the first O2. Signup and view all the answers

What is the primary type of haemoglobin in adults?

Haemoglobin A Signup and view all the answers

Which type of haemoglobin has a greater affinity for oxygen than Haemoglobin A?

Foetal haemoglobin Signup and view all the answers

What is the composition of normal adult haemoglobin A (HbA)?

Two alpha and two beta chains. Signup and view all the answers

Which embryonic haemoglobin is commonly found at birth?

Foetal haemoglobin Signup and view all the answers

How much oxygen can 1g of haemoglobin carry?

1.34 ml O2 Signup and view all the answers

Study Notes

Haemoglobin Lecture Notes

Haemoglobin has a structure allowing it to load and unload oxygen
Different types of haemoglobin exist, including:
- Haemoglobin A (HbA): 95-98% in adults, with two alpha and two beta chains (α₂β₂)
- Haemoglobin A2 (HbA₂): 1.5-3% in adults, with two alpha and two delta chains (α₂δ₂)
- Fetal haemoglobin (HbF): present at birth, at 0-0.5% in adults, with two alpha and two gamma chains (α₂γ₂). Has greater affinity for oxygen than HbA, which facilitates oxygen transfer from mother to foetus.
Haemoglobin abnormalities can cause anaemia and reduced oxygen-carrying capacity in the blood due to insufficient or malformed haemoglobin. Examples include thalassemias (reduced or absent alpha or beta chains) and haemoglobinopathies (abnormal polypeptide chains like haemoglobin C, E, I, J, S).
Haemoglobin S (sickle cell haemoglobin) results from a single amino acid substitution (valine for glutamic acid) in beta globin chains. Low oxygen causes the haemoglobin to change shape, causing cells to become stiff and deformed, clogging blood vessels, leading to pain and anaemia.

Haemoglobin Breakdown

Old or damaged red blood cells (RBCs) are broken down by macrophages within the spleen.
Haemoglobin is broken into haemoglobin and globin components.
Globin is reused or broken down to amino acids.
Haem molecules are broken down first into biliverdin then bilirubin.
Iron is reused in haemoglobin synthesis
Bilirubin is carried by albumin from the spleen to the liver and metabolised there, in the production of bile.
Bilirubin buildup results in jaundice (yellowing skin and eyes).

Haemoglobin Levels and Anaemia

The World Health Organization defines anaemia by haemoglobin levels below:
- 7.7 mmol/L (13 g/dL) in men
- 7.4 mmol/L (12 g/dL) in women.
Abnormally low red blood cell count or haemoglobin concentration can also indicate anaemia.

Laboratory Test Results:

Specific lab results were reported -RBC count -HGB / haemoglobin level -HCT / haematocrit -MCV / mean corpuscular volume -MCH / mean corpuscular haemoglobin -MCHC / mean corpuscular haemoglobin concentration -WBC count -Differential white blood cell count components (e.g., neutrophils, lymphocytes, monocytes, eosinophils, basophils)
- Platelets (PLT) -Serum iron -Total iron binding capacity (TIBC) -Serum Ferritin -Transferrin saturation
Specific examples of results from a patient case were included.

Recommended Textbooks for Immunology

Basic Immunology: Functions and Disorders of the Immune System by Abbas, Abul K., Andrew H. Lichtman, Shiv Pillai, and David L. Baker (7th ed., 2024, Elsevier)
Immunology for Medical Students by Helbert, Matthew, and Roderick Nairn (3rd ed., 2017, Elsevier)

Other Important Points

Co-operative binding: Binding of one oxygen molecule to haemoglobin causes a conformational change in the neighbouring polypeptide chains, increasing the affinity of the haemoglobin for further oxygen molecules.
Oxygen uptake and release.
Normal developmental profile of haemoglobins. This displays the relative percentage of different types of haemoglobin (Hb) throughout development from fetus to newborn.

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Description

This quiz covers the structure and types of haemoglobin, including Haemoglobin A, A2, and fetal haemoglobin. It also discusses haemoglobin abnormalities and their impact on health, such as anaemia and sickle cell disease. Test your knowledge on this essential component of blood function!