A codon is a sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis.
Amino acids play central roles both as building blocks of proteins and as intermediates in metabolism.
The genetic code is traditionally represented as an RNA codon table because, when proteins are made in a cell by ribosomes, it is mRNA that directs protein synthesis. The mRNA sequence is determined by the sequence of genomic DNA. With the rise of computational biology and genomics, most genes are now discovered at the DNA level, so a DNA codon table is becoming increasingly useful