(4) Consequence of base substitution mutation

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Even a small change in bases can result in mutation for example the gene that controls sickle-cell anemia where a change of only one base leads to a protein with one amino acid changing resulting in sickle-cell anemia.


Hemoglobin is made of 4 polypeptide chains: two alpha and two beta.

When an A to T base substitution occurs in the region of the gene coding for the 6th amino acid in the beta chain the codon GAG (glutamic acid) becomes GTG (valine)


The resulting polypeptide is different and the hemoglobin formed is commonly known as HbS: the “normal” hemoglobin is known as HbA

HbS is a slightly different structure: one amino acid makes it crystallize at low


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