GENETIC CODE
Genetic code is a system of recording of hereditary information in molecules of nucleic acids. It serves for transfer of information in the translation process from the nucleotide sequence of a mRNA to the collinear amino acid sequence of a protein. Every amino acid is encoded by a continuous sequence of three nucleotides (triplets), which is called a codon (a codon is an element of a code). Codons in a gene follow each other without overlappings or gaps.
The genetic code serves, vertually, for translation of a 4-letter alphabet into a 20-letter one. There are 43=64 possible triplets for 20 amino acids. Besides the codons defining 20 known amino acids, there are triplets, which form starting and terminating codons. Genetic code is confluent because one or several synonymous codons can correspond to one amino acid; 61 codons represent 20 amino acids.
Another peculiarity of the code is the tendency to grouping of codons, which correspond to one amino acid. Often a base in the third position of a codon is insignificant for its specifity. One amino acid can be represented by four codons, which are different only in their third bases. This property is called degeneracy of the third base.
Jne more important property of the genetic code is its universality. The most part of various proteins of prokaryotes and eukaryotes are encoded with the help of the universal genetic code. Significant difference is found only in mitochondria. Mitochondrial genetic code is specfic: it is different for every species.
|
Supplementary information
|