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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.
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.
- 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. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.1845#1872.