 This messenger RNA molecule is then used to produce a corresponding amino acid sequence through a process called translation . Each group of three nucleotides in the sequence , called a codon , corresponds either to one of the twenty possible amino acids in a protein or an instruction to end the amino acid sequence ; this correspondence is called the genetic code . The flow of information is unidirectional : information is transferred from nucleotide sequences into the amino acid sequence of proteins , but it never transfers from protein back into the sequence of DNA — a phenomenon Francis Crick called the central dogma of molecular biology . 
