Question

Polypeptide synthesis occurs before a red blood cell is released into the circulation.
The HBB gene codes for the β-globin polypeptide of haemoglobin.
There are two alleles of HBB, known as HbA and HbS.
Describe the difference between the HbA allele and the HbS allele and state how this
difference affects:
• the β-globin polypeptide
• the haemoglobin molecule

Answer 1

HbS gene is the allele of haemoglobin producing gene also known as Sickle Haemoglobin.

HbA gene is another allele also known as Normal Haemoglobin.

Difference and it's result.

• Sickle haemoglobin differs from normal haemoglobin by a single amino acid: valine replaces glutamate at position 6 on the surface of the β-globin polypeptide of haemoglobin.

• Haemoglobin tetramers stick to each other, forming long fibers (i.e., polymerizing) instead of remaining independent.

• The polymerized haemoglobin distorts red blood cells into an abnormal sickle shape.

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