Base triplet

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A base triplet consists of three successive nucleobases of a nucleic acid . In biochemistry and molecular biology, this denotes a triplet of the base sequence in the sequence of nucleotides of a DNA or RNA strand that can represent a codon .

The specific sequence of bases in a triplet represents the smallest meaningful unit of the genetic code , a codon. Since one of four different nucleobases occurs at each of the three positions of a triplet, there are 4 3 = 64 possible combinations (as a variation with repetition ) for three successive bases and thus 64 codons. In the base sequence of a nucleic acid, a certain base triplet as a start codon (for example AUG) can represent the beginning or a certain other base triplet as a stop codon (for example UAA) the end of a coding nucleic acid segment. Within the open reading frame thus determined , a base triplet then codes for an amino acid , in accordance with the genetic code.

The sequence of the bases of nucleotides in a certain reading direction ( 5 '→ 3' ) with the same reading frame in non-overlapping steps of three - the triplets - is read in a reading frame . Such is the ribosome in translation codon of a base triplets of mRNA by base pairing the complementary anticodon of the base triplets of a tRNA associated with and above each have a specific amino acid . In this way, a specific nucleotide sequence of the nucleic acid is translated into a specific amino acid sequence of the polypeptide chain formed and thus determines the primary structure of a protein .

In the double strand of DNA , that strand whose section serves as a single-stranded template for the RNA transcript is referred to as the template strand , the non-coding strand or the codogenic strand . Its base triplets, which are complementary to the base triplet of a codon, are called codogens . The other strand of DNA that does not serve as a template is called the non- template strand , non-codogenic or “coding” because its base sequence is similar to that of the coding RNA transcript.


Francis Crick was able to show in 1961 that the genetic code is based on triplets.

Individual evidence

  1. For the term “coding” for one of the two DNA strands see JCBN / NC-IUB Newsletter 1989 ; compare also nomenclature conventions or coding strand in Lexikon der Biochemie on , accessed on November 24, 2015.
  2. FH Crick et al: General nature of the genetic code for proteins. In: Nature. Volume 192, 1961, pp. 1227-1232. PMID 13882203 doi: 10.1038 / 1921227a0 (PDF) .