The universal genetic code is the logical mapping that specifies how genetic
information stored in DNA and mRNA determines protein sequence. It was discovered
by Watson and Crick and since then was found to be common to all living organisms,
with only minor and rare differences. Each triplet of bases is called a codon,
and codes for a specific amino acid. There are also special codons, called stop
codons, which are used to signal the termination of the protein synthesis
process. Along with coding for the methionine amino acid, the
AUG codon is a part of the signal for the beginning of the
translation (it marks the starting point of the translation). Since there are 64 possible codons (minus three stop codons), and only
20 amino acids, different codons may be used to code for the same
amino acid. The genetic code may be seen as a function from
the 43 possible codons to the 20 amino acids plus stop.
