Genetic code and its characteristics.

Date: 2015-10-07; view: 519.

Genetic code is particular sequences of nucleotides in the DNA corresponding the particular sequences of amino acid in the peptide.

The theory of genetic code for the first time worded by George Gamow (1954) and complemented by Francis Crick (1961).

The genetic code of DNA has common characteristics for all vital organisms. Characters of genetic code are:

- The genetic code has triplet nature. Thus the sequence of three consecutive bases (termed as a codon) in a DNA molecule codes for one specific amino acid.

- The genetic code is universal. Universality means the given codon in the DNA and mRNA specifies the same amino acid in the protein-synthesizing stems of all vital organisms.

- The genetic code is no overlapping. The adjacent codons do not overlap, i.e., etch bases of the DNA belongs to one triplet (codon) only.

- The genetic code is redundant. Redundancy or degeneracy (lacks specificity) mean one amino acid codes by several codons. The redundancy exists due to the fact that there are about 20 amino acids and there are 64 possible triplets.

- The genetic code is no punctuation. No punctuation means the genetic code has no “punctuation marcs” (gaps) between the coding triplets. Thus Genetic code is unceasing.

- Majority of codons have a sense but there are 3 of the 64 codons, that are terminator codons or “nonsense” codons (UAA, UAG, and UGA).

- Colinearity. DNA is a linear polynucleotide chain and a protein is a linear polypeptide chain. The sequence of amino acids in polypeptide chain corresponds of nucleotide bases in the gene.

- Gene-Polypeptide parity. A specific gene transcribes a specific mRNA, which produces a specific polypeptide.

Genetic code