WHY BIOLOGICAL ALPHABETS HAS 4 AND 20 LET TERS

An attempt is made to explain why the biological alphabets whose lette rs denote polynucleotides and polypeptides consist of 4 and 20 letters . It is suggested that the letters-molecules constituting the alphabet s are described by a few physico-chemical properties (features) having several levels of manifestation. The letter is considered as the comb ination of features and levels. The simplest set realized in a chemica l (biochemical) system contains 4, while the next in order of complexi ty has 20 combinations which correspond to the letters of the alphabet s. The suggested approach can likely be used for consideration of ling uistic alphabets.