Polar, Uncharged Amino Acids

The side chains of glutamine (Gln or Q) and asparagine (Asn or N) amide derivatives of Asp and Glu, respectively, are uncharged but may participate in hydrogen bonding.  Due to the reactive hydroxyl group in the side-chain Serine (Ser or S) and threonine (Thr or T) are polar amino acids, and can  also  participate  in  hydrogen  bonding  (as  may  the  hydroxyl  group  of  the aromatic amino acid Tyr).

The standard amino acids. (a) Polar, charged R groups, (b) polar, uncharged R groups.