Question

Draw the structure of a 3-mer containing leucine, histidine, and glutamic acid in the ionic form that predominates at pH 7.

Please explain all the steps and so I can read it :)

Answer 1

3-mer is formed by the formation of peptide bond between carboxyl group of one Amino acid and Amino group of another Amino acid. Thus, two peptide bonds (CO-NH linkages) are formed in 3 mer. There is more than one sequence of these Amino acids are possible. Structure of 3-mer is :

All groups whose pKa is less than pH will exist in deprotonated form and groups whose pKa is greater than pH will exist in protonated form. Thus all Carboxylic group and histidine side chain exist in deprotonated form because their pKa is less than 7.

So net charge is -1