Genetic Code is Universal

Genetic Code is Universal

Genetic Code is Universal -
The genetic code is valid for all organisms ranging from bacteria to man. It is essentially the same for an organism and is therefore said to be universal.

The universality of the code was demonstrated by Marshall, Caskey and Nirenberg (1967), who found that E. coli (bacterium), Xenopus laevis (amphibian) and guinea pig (mammal) amino acyl tRNAs use almost the same code.

This showed that the code is essentially universal.Other evidence for the universality of the code comes from a study of gene mutations.

Such mutations result in amino acid substitutions. Amino acid substitution resulting from gene mutations are known for coat protein in tobacco mosaic virus (TMV),

Ct chain of tryptophan synthetase in E. coli and haemoglobin in man. A change in a single base can account for nearly all amino acid substitutions. This proves the universality of the code.

The code has remained contant since the time it was fixed when complex bacteria evolved (about three billion years ago). Any mutation altering the code reading would change the reading of mRNA.

This in turn may change the amino acid sequence of the proteins synthesized by the organism.As many of these changes could be lethal, there would be a strong selection pressure against such a mutation.

Hence the constancy of the code over a long period of time. Changes in protein take place only with respect to the positions of particular amino acids.

Moreover, only a few such changes take place at a time. Most mutation result in only a single amino acid substitution.

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Third Base Deciphering the Code Use of Polymer Containing a Single Type of Nucleotide (Homopolymers) Use of Mixed Polymers with Random Sequences (Heteropolymers) Use of Mixed Polymers with Defined Sequences (Heteropolymers) Use of Trinucleotides in Filter Binding (Minimessengers) Genetic Code is Universal Colinearity of Gene Structure and its Polypeptide Product

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