Illustrate Hbonding interactions using the side chains of Ty

Illustrate H-bonding interactions using the side chains of Tyr and His

Solution

Hydrogen bond is the non covalent electrostatic attraction between H atom bonded to an electropositive atom and other electronegative atom. Due to difference between electronegativity, the hydrogen atom and the other electronegative atom carry partial positive and partial negative charge respectively, thereby creating a dipole. This is seen in tyrosine and histidine amino acids. Since tyrosine carries no charge at pH 7 and its aromatic polar side chain bears lone pair of electons on oxygen (OH group), it serves as hydrogen bond acceptor and can form H bond with an electropositive atom having one H atom. Since histidine has partially protonated side chain at pH 7, it serves as H bond donor. So, tyrosine and histidine can form H bond at pH 7 wherein tyrosine would serve as hydrogen bond acceptor and histidine as hydrogen bond donor.