Universal among all life forms, the genetic code is the language used to write the mRNA instructions for building proteins. Each three-letter codon in the mRNA specifies a particular amino acid. Since there are 20 different amino acids and 64 different codons, an amino acid can be represented by more than one codon. The methionine codon (AUG) is the start codon initiating protein synthesis. Three stop codons signify the end of a protein sequence.
Credit or Source: Biological and Environmental Research Information System, Oak Ridge National Laboratory
US DOE. Genomics Placemat: Genomics for Energy and Environmental Science, US Department of Energy Office of Science. (p. 1) (website)