Genetic code
Rules translating nucleotide triplets into proteins.
The genetic code is the system that living cells use to turn the information in DNA or RNA into proteins. This information is carried in sequences of three-nucleotide units called codons. The ribosome carries out the translation process, linking amino acids in the order dictated by messenger RNA, while transfer RNA molecules bring the correct amino acids and read the mRNA three bases at a time. This code is nearly identical across all life forms and can be summarized in a simple table of 64 entries.
After the structure of DNA was discovered in 1953, scientists began investigating how proteins are encoded. Francis Crick and James Watson, who discovered DNA's structure at the University of Cambridge, proposed that information flows from DNA and that a link exists between DNA and proteins. George Gamow was the first to offer a practical scheme for protein synthesis from DNA. He suggested that sets of three bases, or triplets, were needed to encode the 20 standard amino acids, allowing for up to 64 possible codons. He called this idea the "diamond code." In 1954, Gamow founded the RNA Tie Club, an informal group for scientists interested in how genes produce proteins. The club had 20 permanent members, one for each amino acid, plus four honorary members representing the four DNA nucleotides. Crick's first contribution to the club was a paper titled "On Degenerate Templates and the Adaptor Hypothesis," which proposed that the triplet code was not passed directly to amino acids but instead carried by an adaptor molecule. This adaptor was later identified as transfer RNA.
Experiments by Crick, Brenner, Barnett, and Watts-Tobin first showed that codons consist of three DNA bases. In 1961, Marshall Nirenberg and J. Heinrich Matthaei used a cell-free system to translate a string of uracil bases (UUUUU...) and found it produced a polypeptide made only of the amino acid phenylalanine, revealing that the codon UUU specifies phenylalanine. Severo Ochoa's lab then showed that a poly-adenine sequence (AAAAA...) coded for poly-lysine and a poly-cytosine sequence (CCCCC...) coded for poly-proline, identifying AAA as lysine and CCC as proline. Using various copolymers, most remaining codons were determined. Har Gobind Khorana completed the rest of the genetic code, and Robert W. Holley determined the structure of transfer RNA, the adapter molecule. Nirenberg and Philip
- field
- Molecular biology, genetics
- known_for
- The canonical set of rules translating nucleotide triplets into amino acids during protein synthesis
Lore & Background
Efforts to understand how proteins are encoded began after DNA's structure was discovered in 1953. Francis Crick and James Watson hypothesized that information flows from DNA and that there is a link between DNA and proteins. George Gamow was the first to give a workable scheme for protein synthesis from DNA, postulating that sets of three bases (triplets) must be employed to encode the 20 standard amino acids, allowing a maximum of 64 possible codons. He named this DNA–protein interaction the 'diamond code'. In 1954, Gamow founded the RNA Tie Club for scientists interested in how proteins were synthesised from genes. The club could have only 20 permanent members to represent each of the 20 amino acids and four additional honorary members to represent the four nucleotides of DNA. Crick presented a paper titled 'On Degenerate Templates and the Adaptor Hypothesis' to th
Reader's Guide
The genetic code is fundamental to all life, providing the mechanism by which genetic information is translated into proteins. The 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, using a cell-free system to translate a poly-uracil RNA sequence and discovering that the codon UUU specified phenylalanine. Subsequent work by Severo Ochoa's laboratory demonstrated that poly-adenine coded for poly-lysine and poly-cytosine for poly-proline. Har Gobind Khorana identified the rest of the genetic code, and Robert W. Holley determined the structure of transfer RNA. Nirenberg and Philip Leder revealed the code's triplet nature and deciphered its codons, determining sequences of 54 out of 64 codons. The three stop codons were named by Richard Epstein and Charles Steinberg: amber, ochre, and opal. Since 2001, 40 non-natural amino acids have been added into proteins by creating unique codons and corresponding tRNA-synthetase pairs. In 2015, researchers reported full substitution of all tryptophan residues with unnatural thienopyrrole-alanine in E. coli. In 2016, the first stable semisynthetic organism was created with two synthetic bases. In 2017, researchers engineered a mouse with an extended genetic code. In May 2019, researchers created a 'Syn61' strain of E. coli with a fully synthetic genome that removed three codons. In 2025, researchers reported a 'Syn57' strain removing seven codons.
Did You Know?
- George Gamow was the first to give a workable scheme for protein synthesis from DNA, naming it the 'diamond code'.
- The three stop codons were named amber, ochre, and opal by discoverers Richard Epstein and Charles Steinberg.
- Marshall Nirenberg and J. Heinrich Matthaei were the first to reveal the nature of a codon in 1961 using a poly-uracil RNA sequence.
- In 2016, the first stable semisynthetic organism was created with two synthetic bases called X and Y.
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