The genetic code establishes a correspondence between the array of nucleic acids and the polypeptide product (An amino acid corresponds to a codon). The genetic code is written in Mrna rather than the DNA. The most interesting aspect of the genetic code is that some amino acids are encoded by several codons related but different. Among a total of 64 codons, 4 are dedicated to the initiation and arrest of translation;

Figure 13: Correspondence between the triplet of bases in the Mrna and the amino acids and the nonsense (stop codon).

-The codon AUG (code for formyl-MET or MET) = initiation codon

-The first nucleotide of the first codon determines the open reading frame (ORF: Open Reading Frame).

-There are 64 possible combinations of the nucleotides in codons (43). As there are 20 amino acids, so there are 44 codons additional :

Ø  3 correspond to stop codons or nonsense :UAA, UAG, and UGA

Ø  The others are synonyms that encode different acids amino (Degeneration of the genetic code)

-Code UNIVERSAL: it is the same for all living beings except for a few rare exceptions. This feature allows the transfer of genes from one species to the other = genetic engineering.