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Standard genetic code

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The standard genetic code[1] is the list of codons, made up of triplet bases on RNA, that provide instructions for which amino acid to add to a growing protein chain. The codon triplets are three sequential bases which can include adenine (A), cytosine (C), guanine (G) or uracil (U). The codon for the amino acid methionine is also the start codon in mRNA used to initiate protein production. These codons are made to interact with the corresponding anti-codon in transfer-RNA molecules (tRNA). Although some amino acids have only one codon, such as AUG for methionine, other amino acids are indicated by several codons. Thus, proline has four codons, CCU, CCC, CCA and CCG. This means there is a one-to-one correspondance in going from codon to amino acid, but not from an amino acid to codons. There is only one start codon, AUG, which serves as the codon for methionine, but there are three stop codons, UAA, UAG and UGA. The sequence of codons in mRNA is derived from the sequence present in the DNA from which the mRNA was transcribed.

1 2 3
U C A G
U Phe Ser TYR Cys U
Phe Ser Tyr Cys C
Leu Ser Stop Stop A
Leu Ser Stop Trp G
C Leu Pro His Arg U
Leu Pro His Arg C
Leu Pro Gln Arg A
Leu Pro Gln Arg G
A Ile Thr Asn Ser U
Ile Thr Asn Ser C
Ile Thr Lys Arg A
Met Thr Lys Arg G
G Val Ala Asp Gly U
Val Ala Asp Gly C
Val Ala Glu Gly A
Val Ala Glu Gly G

References

  1. Biochemistry, 3rd Ed, Lubert Stryer, 1988, W. H. Freeman and Co, New York.