Will all organisms with the same 3 nucleotide sequence in the codon produce the same exact same amino acid. I read that the three nucleotide sequence will code for a particular amino acid. I did not understand if that is the case across organisms. Can someone explain this in simple terms.

  • $\begingroup$ Yes. One particular sequence of codon code for only and only one amino acid. However, there could be more than one codons for a single amino acid. $\endgroup$
    – Beginner
    Oct 23, 2016 at 6:15
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    $\begingroup$ @Beginner Please follow the instructions for comments and do NOT use them to answer questions. In this case you also happen to be wrong as I will explain and reference in an answer. $\endgroup$
    – David
    Oct 23, 2016 at 8:18
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    $\begingroup$ I think it better to not treat this as a duplicate of the mitochondrial question. This question is even more basic, and one that can be answered straightforwardly and without the confusing twist of context resulting from using that question. $\endgroup$
    – mgkrebbs
    Oct 23, 2016 at 18:00
  • $\begingroup$ Are you interested in the different codons used across organsims or the different codons used (based on bias, environment etc.) that code for a specific amino acid? $\endgroup$
    – KingBoomie
    Oct 24, 2016 at 10:13
  • $\begingroup$ @mgkrebbs OK. I have relented and added an answer focussed at the non-mitochondrial situation. $\endgroup$
    – David
    Oct 24, 2016 at 16:58

1 Answer 1


Although the answer to this question may be found in Mitochondrial Genetic code, because that answer is primarily about mitochondrial genetic codes, I shall give a more directed answer here.

Because the same genetic code that was elucidated in bacteria was found to apply to higher eukaryotes, it was initially assumed that the genetic code was universal, and was referred to as such. Subsequently it was discovered that mitochondria did not generally employ this ‘universal’ code, which is now usually referred to as the ‘standard’ code — indeed different mitochondrial codes were found in different organisms.

However the question seems to be more concerned with the genetic codes of bacteria and the nuclear genetic codes of eukaryotes. Here also there are deviations from the standard genetic code, which can be found listed either on this Wikipedia page or at NCBI.

Below are some examples from the NCBI list (where references may be found) with the standard coding in parentheses:

 UGA      Trp          (Ter)

 Ciliates, Dasycladacean and Hexamita
 UAA      Gln          (Ter)
 UAG      Gln          (Ter)

 UGA      Cys          (Ter)

 Candidate Division SR1, Gracilibacteria
 UGA      Gly          (Ter)

 Pachysolen tannophilus
 CUG      Ala          (Leu)

Finally, tRNAs for the ‘additional’ amino acids, selenocysteine and pyrrolysine recognize, respectively, the UGA and UAG stop codons in specific contexts.


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