Draw the complete structure of the following pairs of amino acid residues (side chains only) as they would be at pH 8.

Which pair(s) could interact with each other by their side chains forming a hydrogen bond?

Indicate clearly how each pair could interact through hydrogen bonding, by drawing a dotted line to indicate the hydrogen bond.

Label clearly the donor and acceptor atoms in each hydrogen bond.
i) val - ser
ii) lys - his
iii) asn - tyr

Which hydrogen bonding interaction would be affected if the pH were lowered to 5? Explain briefly why it would change.