Editing DNA (section)

=== Transcription and translation ===
{{further|Genetic code|Transcription (genetics)|Protein biosynthesis}}
A gene is a sequence of DNA that contains genetic information and can influence the [[phenotype]] of an organism. Within a gene, the sequence of bases along a DNA strand defines a [[messenger RNA]] sequence, which then defines one or more protein sequences. The relationship between the nucleotide sequences of genes and the [[amino acid|amino-acid]] sequences of proteins is determined by the rules of [[Translation (biology)|translation]], known collectively as the [[genetic code]]. The genetic code consists of three-letter 'words' called ''codons'' formed from a sequence of three nucleotides (e.g. ACT, CAG, TTT).

In transcription, the codons of a gene are copied into messenger RNA by [[RNA polymerase]]. This RNA copy is then decoded by a [[ribosome]] that reads the RNA sequence by base-pairing the messenger RNA to [[transfer RNA]], which carries amino acids. Since there are 4 bases in 3-letter combinations, there are 64 possible codons (4<sup>3</sup>&nbsp;combinations). These encode the twenty [[list of standard amino acids|standard amino acids]], giving most amino acids more than one possible codon. There are also three 'stop' or 'nonsense' codons signifying the end of the coding region; these are the TAG, TAA, and TGA codons, (UAG, UAA, and UGA on the mRNA).