Normal adult haemoglobin contains?

Appeared in: NVS- 2025

Explanation

Normal adult hemoglobin (HbA) is a protein made of four subunits, making it a tetramer.
It specifically consists of two alpha (α) globin chains and two beta (β) globin chains.
This α₂β₂ structure is essential for its function of efficiently binding and transporting four molecules of oxygen throughout the body.
HbA constitutes over 95% of the total hemoglobin in a healthy adult.

Option A: This describes a dimer (two chains), but hemoglobin is a tetramer (four chains).
Option B: This describes a trimer (three chains) with an incorrect ratio. The structure of HbA is symmetrical, requiring an equal number of alpha and beta chains.
Option C: This also describes a trimer with an incorrect and asymmetrical ratio. HbA requires a 2:2 ratio of alpha to beta chains.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Structure of Adult Hemoglobin (HbA) as background academic context rather than a clinical decision trigger.
Understanding the α₂β₂ structure is fundamental for diagnosing hemoglobinopathies. For instance, sickle cell disease results from a point mutation in the β-globin gene, altering the shape and function of the entire hemoglobin molecule.
Thalassemias are quantitative disorders where the production of either alpha or beta chains is reduced or absent, leading to an imbalance in globin chain synthesis and ineffective red blood cell production.
What if? If the question had asked about the major hemoglobin in a fetus, the correct answer would be two alpha and two gamma chains (α₂γ₂). This is Fetal Hemoglobin (HbF), which has a higher affinity for oxygen, facilitating oxygen transfer from the mother's circulation.

How to Approach the Question

Identify the core concept of the question, which is the composition of 'normal adult hemoglobin'.
Recall that hemoglobin is a complex protein with a quaternary structure, meaning it is composed of multiple polypeptide subunits.
Remember that the primary adult form (HbA) is a tetramer, meaning it has four subunits. This fact helps to eliminate options suggesting fewer than four total chains.
Recall the specific composition of HbA, which is a symmetrical arrangement of two alpha (α) and two beta (β) chains.
Evaluate the options based on this knowledge. Only 'Two alpha chains and two beta chains' matches the correct α₂β₂ structure.

Concept Tested & Keywords

QG7fVIMdwldt9HumcKH9Qq

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 715-717

E6 Medicine Harrison 22e Part 1 p. 811-813

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Practise the full NVS- 2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.