Polar amino acids

 Polar amino acids
There are twenty amino acids, five of which are polar but uncharged. Two of which contain a hydroxyl group (-OH) attached to aliphatic side chain that is serine and threonine. As for the aspargaine and glutamine they contain a terminal carboxamide in place of carboxylic acid. The fifth polar amino acid is cysteine that is structurally similar to serine but contain a sulfhydryl, or thiol (-SH), instead of the hydroxyl (-OH) group.
{| width="200" border="1" cellpadding="1" cellspacing="1" |+ Polar amino acids |- | Serine | Ser | S |- | Cysteine | Cys | C |- | Threonine | Thr | T |- | Glutamine | Gln | Q |- | Asparagine  | Asn | N |}