[The evolution of the structures of amino acid families]

Natural amino acids possessing common antiamino acids are divided into groups and families according to the genetic code algorithm a-n-n-a (amino acid-codon-anticodon-antiamino acid). In an attempt to study structural evolution of amino acid families, artificial genetic code models were constructed. It is suggested that after inclusion of asparaginase and glutamine into the coding system, one of the two natural amino acid families is split into two parts ("half-families").