The  nearly  universal  genetic  code
   serves as a dictionary for translation from mRNA to amino acid.

   The  triplet  code  provides  64  (4^3) codons to specify the 20 amino
   acids.

   Thus  the  code is degenerate: many amino acids specified by more than
   one  codon;  only  tryptophan  and  methionine are encoded by a single
   codon.

   In  addition to codons that specify amino acid, there is one start (or
   initiation)  codon  (AUG,  which  also  encodes methionine) and 3 stop
   (termination) codons.