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 exceptions of six amino acid residues, as shown below. Is the pI of human insulin lower than or higher than that of duck insulin? Amino acid residue A8 A9 A10 B1 B2 B27 Human Thr Ser Ile Phe Val Thr Duck Glu Asn Pro Ala Ala Ser I don't understand how to find the pI of residues, since the reading says it can only be found experimentally. Should I just be comparing the pI for each free amino acid between ducks and humans? Please explain the answer instead of just giving the solution.