Editing Reading frame (section)

== Genetic code ==
{{Main|Genetic code}}DNA encodes protein sequence by a series of three-nucleotide [[codon]]s. Any given sequence of DNA can therefore be read in six different ways: Three reading frames in one direction (starting at different nucleotides) and three in the opposite direction. During [[Transcription (biology)|transcription]], the RNA polymerase read the template DNA strand in the 3′→5′ direction, but the mRNA is formed in the 5′ to 3′ direction.<ref>{{cite book |title = Molecular Cell Biology |edition = 6th |last = Lodish |year = 2007 |publisher = W. H. Freeman |isbn = 978-1429203142 |page = 121 }}</ref> The mRNA is single-stranded and therefore only contains three possible reading frames, of which only one is [[Translation (biology)|translated]]. The codons of the mRNA reading frame are translated in the 5′→3′ direction into [[amino acids]] by a [[ribosome]] to produce a [[polypeptide|polypeptide chain]].