Sickle cell anaemia is a well-known inherited disease caused by a point mutation in the gene encoding the -globin chain of human haemoglobin. Which of the following alterations at the primary protein structure level directly causes the formation of abnormal haemoglobin S (HbS)?
- Replacement of glutamic acid with valine at the sixth position of the -globin polypeptide chainAnswer
- BDeletion of a nucleotide triplet resulting in the total absence of the -globin chain
- CNondisjunction resulting in an extra copy of the chromosome bearing the globin gene family
- DInversion of a chromosome segment containing the genes responsible for ABO blood grouping
Answer
The formation of abnormal haemoglobin S (HbS) in sickle cell anaemia is caused by the replacement of glutamic acid with valine at the sixth position of the -globin polypeptide chain.
Sickle cell anaemia is caused by a single nucleotide substitution in the -globin gene located on chromosome 11, where adenine is substituted by thymine. This alters the mRNA codon from GAG to GUG, causing valine to replace glutamic acid at the 6th position of the -chain, leading to polymerisation of haemoglobin molecules under low oxygen tension.
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Key Concept
Gene Point Mutation and Molecular Consequences in Sickle Cell Anaemia
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