In peptides and proteins (peptides simply being smaller proteins), the amine nitrogens of amino acids are linked to the carboxyl carbons of other amino acids by peptide (aka amide) bonds formed by condensation reactions (i.e., removal of H2O). Consider the free amino acid glycine and a di-, tri-, and tetrapeptide comprised of glycine. Circle the one that would have the terminal amine group (i.e. free; not involved in a peptide bond) with the highest pKa.
(i) amine-Gly-carboxyl (ii) amine-Gly-Gly-carboxyl (iii) amine-Gly-Gly-Gly-carboxyl
(iv) they would all have the same pKa