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Protein Function in Oxygen Transport Quiz
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Which globin chain composition correctly describes foetal haemoglobin?
- A Two alpha chains and two gamma chains You picked ✓
- B Four gamma chains only You picked ✕
- C Two alpha chains and two delta chains You picked ✕
- D Two alpha chains and two beta chains You picked ✕
- E Two beta chains and two delta chains You picked ✕
Correct!
Incorrect
The answer is A: Two alpha chains and two gamma chains
Explanation
Why A is correct
See Foetal Haemoglobin. Option A is correct. Haemoglobin is a tetramer, meaning a molecule built from four globin chains (protein subunits), each carrying a haem group that binds oxygen. Adult haemoglobin (HbA) has two alpha and two beta chains, whereas foetal haemoglobin (HbF) keeps the two alpha chains but replaces the two beta chains with two gamma chains. This small structural difference gives HbF a higher oxygen affinity (it holds oxygen more tightly) than the mother's HbA. In the placenta the oxygen partial pressure in the foetal blood is low, so the foetus needs haemoglobin that can take up oxygen from maternal blood, and HbF does this. Gamma chains are the main non-alpha chain before birth, and beta chains take over in the first months of life as the switch to adult haemoglobin happens.
- Foetal haemoglobin: two alpha chains and two gamma chains.
- Adult HbA: two alpha chains and two beta chains.
- Oxygen affinity: HbF holds oxygen more tightly than maternal HbA, so it takes oxygen up in the placenta.
Why the other options are incorrect
- B. Four gamma chains only: Four gamma chains form haemoglobin Bart's, which appears in severe alpha-thalassaemia when alpha chains are missing. It binds oxygen too tightly to release it, so it is a disease product and not normal foetal haemoglobin. Your answer
- C. Two alpha chains and two delta chains: Two alpha and two delta chains make haemoglobin A2, a minor normal variant found at low levels in adults. It is not the main foetal haemoglobin. Your answer
- D. Two alpha chains and two beta chains: Two alpha and two beta chains make adult haemoglobin, HbA, the main type after infancy. It would be the answer if the question asked about adult haemoglobin. Your answer
- E. Two beta chains and two delta chains: This is not a haemoglobin that occurs in the body, because normal haemoglobin always has two alpha-type chains. Beta and delta chains do not pair up on their own like this. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which molecular change is responsible for the abnormal properties of haemoglobin in sickle cell anaemia?
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2
Which mechanism best explains the tissue hypoxia seen in haemoglobin H disease, a form of alpha-thalassaemia?
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