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Stop codon

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A stop codon is a phrase in the genetic code. It is a codon (that is, any sequence of three nucleotides within messenger RNA) that indicates the end of a gene. Similar to how a full stop indicates the end of a sentence. A stop codon signals the end of genetic translation.[1]

They are also called termination codons or chain termination codons. There are three such codons: UAA, UAG and UGA.

Proteins are based on polypeptides, which are unique sequences of amino acids. Most codons in messenger RNA correspond to the addition of an amino acid to a growing polypeptide chain, which may ultimately become a protein. Stop codons indicate the end of this process, and therefore, the end of protein synthesis.


  1. Griffiths AJF, Miller JH, Suzuki DT, Lewontin RC, and Gelbart WM (2000). "Chapter 10 (Molecular Biology of Gene Function): Genetic code: Stop codons". An Introduction to Genetic Analysis. W.H. Freeman and Company.