3. The protein insulin consists of two polypeptides termed the A and B chains. I

Question

3. The protein insulin consists of two polypeptides termed the A and B chains. Insulins from different organisms have been isolated and sequenced. Human and duck insulins have the same amino acid sequence with the exception of 6 amino acid residues, as shown below. A) Is the pl of human insulin lower or higher than that of duck insulin? Please justify your answer. B) Given these sequence differences, is it possible for these proteins to perform the same function for their respective organism? Amino acid residue A8 A9 A10 B B2 B27 Thr Ser lle Phe Val Thr Glu Asn Pro Ala Ala Ser Human Duck

Explanation / Answer

Ans a) The pI of the duck is higher as compared to the humans because in duck there is a charged amino acid in form of Glutamine. This is because of the fact that all the other amino acids that are different are neutral and does not contribute to major changes. The duck insulin is more acidic which leads to increase in the pI.

Ans b) Yes, despite the change in the sequence of amino acid for insulin, the protein tend to perform the same function in both duck and humans. It is a peptide hormone which is manufactured by pancreas and it allows the body to use sugar or glucose from carbohydrates and helps in storage of energy for future. It helps in maintaining the blood sugar level and it has the similar function almost in all animals.

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