DNA and RNA codon tables

A circular diagram is separated into three rings, broken down into sections labeled with the letters: G, U, A, and C. Each represents a nucleotide found in RNA.
The standard RNA codon table organized in a wheel

A codon table can be used to translate a genetic code into a sequence of amino acids.[1][2] The standard genetic code is traditionally represented as an RNA codon table, because when proteins are made in a cell by ribosomes, it is messenger RNA (mRNA) that directs protein synthesis.[2][3] The mRNA sequence is determined by the sequence of genomic DNA.[4] In this context, the standard genetic code is referred to as translation table 1.[3] It can also be represented in a DNA codon table. The DNA codons in such tables occur on the sense DNA strand and are arranged in a 5-to-3 direction. Different tables with alternate codons are used depending on the source of the genetic code, such as from a cell nucleus, mitochondrion, plastid, or hydrogenosome.[5]

There are 64 different codons in the genetic code and the below tables; most specify an amino acid.[6] Three sequences, UAG, UGA, and UAA, known as stop codons,[note 1] do not code for an amino acid but instead signal the release of the nascent polypeptide from the ribosome.[7] In the standard code, the sequence AUG—read as methionine—can serve as a start codon and, along with sequences such as an initiation factor, initiates translation.[3][8][9] In rare instances, start codons in the standard code may also include GUG or UUG; these codons normally represent valine and leucine, respectively, but as start codons they are translated as methionine or formylmethionine.[3][9]

The first table—the standard table—can be used to translate nucleotide triplets into the corresponding amino acid or appropriate signal if it is a start or stop codon. The second table, appropriately called the inverse, does the opposite: it can be used to deduce a possible triplet code if the amino acid is known. As multiple codons can code for the same amino acid, the International Union of Pure and Applied Chemistry's (IUPAC) nucleic acid notation is given in some instances.

  1. ^ "Amino Acid Translation Table". Oregon State University. Archived from the original on 29 May 2020. Retrieved 2 December 2020.
  2. ^ a b Bartee, Lisa; Brook, Jack. MHCC Biology 112: Biology for Health Professions. Open Oregon. p. 42. Archived from the original on 6 December 2020. Retrieved 6 December 2020.
  3. ^ a b c d Elzanowski A, Ostell J (7 January 2019). "The Genetic Codes". National Center for Biotechnology Information. Archived from the original on 5 October 2020. Retrieved 21 February 2019.
  4. ^ "RNA Functions". Scitable. Nature Education. Archived from the original on 18 October 2008. Retrieved 5 January 2021.
  5. ^ "The Genetic Codes". National Center for Biotechnology Information. Archived from the original on 13 May 2011. Retrieved 2 December 2020.
  6. ^ "Codon". National Human Genome Research Institute. Archived from the original on 22 October 2020. Retrieved 10 October 2020.
  7. ^ a b Maloy S. (29 November 2003). "How nonsense mutations got their names". Microbial Genetics Course. San Diego State University. Archived from the original on 23 September 2020. Retrieved 10 October 2020.
  8. ^ Hinnebusch AG (2011). "Molecular Mechanism of Scanning and Start Codon Selection in Eukaryotes". Microbiology and Molecular Biology Reviews. 75 (3): 434–467. doi:10.1128/MMBR.00008-11. PMC 3165540. PMID 21885680.
  9. ^ a b Touriol C, Bornes S, Bonnal S, Audigier S, Prats H, Prats AC, Vagner S (2003). "Generation of protein isoform diversity by alternative initiation of translation at non-AUG codons". Biology of the Cell. 95 (3–4): 169–78. doi:10.1016/S0248-4900(03)00033-9. PMID 12867081.


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