Editing Genetic code (section)

===Codons===
{{Redirect|Codon}}
{{See also|DNA and RNA codon tables#Translation table 1}}

The [[Crick, Brenner et al. experiment|Crick, Brenner, Barnett and Watts-Tobin experiment]] first demonstrated that '''codons''' consist of three DNA bases. 

[[Marshall Nirenberg]] and [[J. Heinrich Matthaei]] were the first to reveal the nature of a codon in 1961.<ref>{{cite journal|last=Yanofsky|first=Charles|date=9 March 2007|title=Establishing the Triplet Nature of the Genetic Code|journal=Cell|volume=128|issue=5|pages=815–818|doi=10.1016/j.cell.2007.02.029|pmid=17350564|s2cid=14249277|doi-access=free}}</ref> They used a [[cell-free system]] to [[translation (biology)|translate]] a poly-[[uracil]] RNA sequence (i.e., UUUUU...) and discovered that the [[polypeptide]] that they had synthesized consisted of only the amino acid [[phenylalanine]].<ref name="pmid14479932">{{cite journal | vauthors = Nirenberg MW, Matthaei JH | title = The dependence of cell-free protein synthesis in E. coli upon naturally occurring or synthetic polyribonucleotides | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 47 | issue = 10 | pages = 1588–602 | date = Oct 1961 | pmid = 14479932 | pmc = 223178 | doi = 10.1073/pnas.47.10.1588 | bibcode = 1961PNAS...47.1588N | doi-access = free }}</ref> They thereby deduced that the codon UUU specified the amino acid phenylalanine.

This was followed by experiments in [[Severo Ochoa]]'s laboratory that demonstrated that the poly-[[adenine]] RNA sequence (AAAAA...) coded for the polypeptide poly-[[lysine]]<ref name="pmid13946552">{{cite journal | vauthors = Gardner RS, Wahba AJ, Basilio C, Miller RS, Lengyel P, Speyer JF | title = Synthetic polynucleotides and the amino acid code. VII | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 48 | issue = 12 | pages = 2087–94 | date = Dec 1962 | pmid = 13946552 | pmc = 221128 | doi = 10.1073/pnas.48.12.2087 | bibcode = 1962PNAS...48.2087G | doi-access = free }}</ref> and that the poly-[[cytosine]] RNA sequence (CCCCC...) coded for the polypeptide poly-[[proline]].<ref name="pmid13998282">{{cite journal | vauthors = Wahba AJ, Gardner RS, Basilio C, Miller RS, Speyer JF, Lengyel P | title = Synthetic polynucleotides and the amino acid code. VIII | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 49 | issue = 1 | pages = 116–22 | date = Jan 1963 | pmid = 13998282 | pmc = 300638 | doi = 10.1073/pnas.49.1.116 | bibcode = 1963PNAS...49..116W | doi-access = free }}</ref> Therefore, the codon AAA specified the amino acid [[lysine]], and the codon CCC specified the amino acid [[proline]]. Using various [[copolymers]] most of the remaining codons were then determined.

Subsequent work by [[Har Gobind Khorana]] identified the rest of the genetic code. Shortly thereafter, [[Robert W. Holley]] determined the structure of [[transfer RNA]] (tRNA), the adapter molecule that facilitates the process of translating RNA into protein. This work was based upon Ochoa's earlier studies, yielding the latter the [[Nobel Prize in Physiology or Medicine]] in 1959 for work on the [[enzymology]] of RNA synthesis.<ref name="Nobel_1959">{{cite press release |url=http://nobelprize.org/nobel_prizes/medicine/laureates/1959/index.html |title=The Nobel Prize in Physiology or Medicine 1959 |quote=The Nobel Prize in Physiology or Medicine 1959 was awarded jointly to Severo Ochoa and Arthur Kornberg 'for their discovery of the mechanisms in the biological synthesis of ribonucleic acid and deoxyribonucleic acid'. |publisher=The Royal Swedish Academy of Science |date=1959 |access-date=2010-02-27}}</ref>

Extending this work, Nirenberg and [[Philip Leder]] revealed the code's triplet nature and deciphered its codons. In these experiments, various combinations of [[mRNA]] were passed through a filter that contained [[ribosome]]s, the components of cells that [[Translation (biology)|translate]] RNA into protein. Unique triplets promoted the binding of specific tRNAs to the ribosome. Leder and Nirenberg were able to determine the sequences of 54 out of 64 codons in their experiments.<ref name="pmid5330357">{{cite journal | vauthors = Nirenberg M, Leder P, Bernfield M, Brimacombe R, Trupin J, Rottman F, O'Neal C | title = RNA codewords and protein synthesis, VII. On the general nature of the RNA code | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 53 | issue = 5 | pages = 1161–8 | date = May 1965 | pmid = 5330357 | pmc = 301388 | doi = 10.1073/pnas.53.5.1161 | bibcode = 1965PNAS...53.1161N | doi-access = free }}</ref> Khorana, Holley and Nirenberg received the Nobel Prize (1968) for their work.<ref name="Nobel_1968">{{cite press release |url=http://nobelprize.org/nobel_prizes/medicine/laureates/1968/index.html |title=The Nobel Prize in Physiology or Medicine 1968 |quote=The Nobel Prize in Physiology or Medicine 1968 was awarded jointly to Robert W. Holley, Har Gobind Khorana and Marshall W. Nirenberg 'for their interpretation of the genetic code and its function in protein synthesis'. |publisher=The Royal Swedish Academy of Science |date=1968 |access-date=2010-02-27}}</ref>

The three stop codons were named by discoverers Richard Epstein and Charles Steinberg. "Amber" was named after their friend Harris Bernstein, whose last name means "amber" in German.<ref>{{cite journal|date=Oct 2004|title=The genome of bacteriophage T4: an archeological dig|journal=Genetics|volume=168|issue=2|pages=575–82|pmc=1448817|pmid=15514035|vauthors=Edgar B|doi=10.1093/genetics/168.2.575}}</ref> The other two stop codons were named "ochre" and "opal" in order to keep the "color names" theme.