Codon tables describe how the triplet codon of RNA (or DNA) is read by specific tRNAs to map to a particular amino acid. Many organisms use the Standard Codon Table, shown below.
Standard Codon table
1The codon ATG both codes for methionine and serves as an initiation site: the first ATG in an mRNA's coding region is where translation into protein begins.
2UGA can also code for selenomethionine: the twenty-first amino acid, discovered in 1986.
3UAG can also code for pyrrolysine: the twenty-second amino acid, discovered in 2002.