General characteristic of genetic code

presentation explain the general Characteristic of genetic code as well as biological significance of the degeneracy.

1. General Characteristic of Genetic Code. Akshay Wakte

2. Genetic Code : The relationship between the sequence of bases in DNA /RNA and the sequence of amino acids in a polypeptide chain of protein / enzyme is called as GENETIC CODE. It contain base sequence of DNA. The term was coined by “ Goerge Gamow” Examples : AUG, UUU, ACC, UAG, etc. The characteristics of genetic code are explain as follows,

3. Triplet Genetic Code : DNA contains four kinds of Nitrogenous bases(A,T,G,C) which forms Amino acid… In Singlet code having 1 base have 4 codons which form 4 amino acid, Similarly in Doublet Code having 4 bases codes for 16 AA ..And in Triplet code having 3 bases codes for 64 AA.. For 20 AA , Third case most suitable…..

4. Code Is Commaless : The Genetic Code has no bases (Commas) between successive codons and arranged in a definite manner i.e. one triplet after another…

5. Code Is Non-overlapping : In non-overlapping code, each nitrogen base is read only once and six nucleotides would code for two amino acids But in overlapping code , one nitrogen base would be read three times, each time as a part of different code and six nucleotides would code for 4 AA. C A T G A T ( Non–Overlapping code) aa1 aa2

6. The Genetic Code Has Polarity : The genetic code must be read in fixed direction i.e. the code has polarity. Always read from left to right (5’ 3’) direction rise to correct protein /enzyme. If the code is read from opposite direction then protein will change and undergo drastic change. UUG AUC GUC 5’ 3’ Leu Ileu Val Val Leu Leu 3’ 5’

7. Initiation Codon And Termination Codon : AUG is starting or initiation codon and initiates the protein synthesis of polypeptide chain. AUG codes for aa Methionine in eukaryotes and N- formyl methionine in prokaryotes. Less often, GUG also serve as intiation codon which codes for Valine … UAG, UAA and UGA are the termination codon . This codons do not specify any amino acid so, is called as Nonsense codon . They terminates the protein synthesis…

8. Universality, Non-ambiguous Nature And Colinearity : Nirenberg demonstrated the universality of the code. A codon specifies the same amino acid from bacteria to tree and human being, etc. and hence it is biologically universal . Non-ambiguous means that a particular codon will always code for the same amino acid. If codon code for another amino acid in presence of external factor, then it said to ambiguous. The sequence of codon in DNA or mRNA corresponds to the sequence of amino acid in the polypepetide manufactured under the guidance of mRNA so, it has colinearity .

9. Code Is Degenerate : There are 61 codons which codes for 20 different amino acids, it is obvious that, there are many more codons than amino acids. Except for tryptophan and methionine , which have a single codon each, all other amino acids have more than one codon (2 to 6 codon ) and they are called as degenerate codons . In this codon , the first two nitrogen bases are similar while the third one is different. As the third nitrogen base has no effect on coding, it called as wobble position .

10. Biological Significance Of Degeneracy : The effect of mutation is reduced. The number of tRNA required is reduced. Degeneracy is also help in evolution of organisms. Degeneracy is help in repair mechanism of various types of mutations.