Fidelity of translation or protein synthesis:
The fidelity or accuracy of
protein synthesis depends on the accuracy of the two mechanisms: linking of
each amino acid to it's corresponding tRNA molecule and the base pairing of the
codons in mRNA to the anticodons in tRNA
Two fundamentally different proofreading mechanisms are used in the cell. Both
are active processes.
One mechanism caller chemical proof reading
is used to improve the accuracy of amino acid attachment to tRNA. This is
carried out by aminoacyl tRNA synthetase, which recognize an incorrect amino
acid attached to its tRNA molecule and remove it by hydrolysis.
A secand mechanism called kinetic proof reading, is used to improve the fidelity of Color - anticodon pairing. Once, t-RNA molecules have acquired an anino acid, they form a complex with an elongation factor (EF). This complexe pairs with the appropriate coden in an mRNA molecule. The bound elongation factors allows correct Codon- anticodon pairing to occur, but prevents the amino acid from being incorporated into the growing polypeptide chain. The elongation factor, Thereby, introduces a short delay between codon - anticodon, base paining and polypeptide chain elongation which provides an opportunity for the bound tRNA molecule to exit from the ribosome. An incerut tRNA molecule firms a smaller no. Of codon anticodon hydrogen bonds then a correct one, it therefore binds more weakly to the ribosome and is more likely to dissociate during this period. Thus, the delay introduced by the elongation factor caused most incorrectly bound tRNA molecules to leave the ribosome without being used for protein synthesis.