Question

(Molecular Biology) What is the "second genetic code" and how does it relate to tRNA and synthetases? How many different synthetases are there in total in most organisms and why is their specificity important?

Answer 1

1. Second genetic code refers to the amino acid recidues of a protein which determine its secondary and teritary structure, or it refers to the feature of tRNA molecule that helps to make it recognizable by one amino acid synthetase.
2. tRNA identity is known as second genetic code, tRNA recognition involves positive identity elements and negative identity elements.
3. Aminoacyl-tRNA is an enzyme that helps to attach appropriate aminoacid onto its tRNA, it is done by catalyzing the esterification of specific congnate amino acid.
4. There are 20 different types of aa-tRNA present, and they are made by 20 different aminoacyl-tRNA synthetases, one for each aminoacid of the genetic code.
5. The synthetase first binds ATP and to the corresponding aminoacid forming aminoacyl-adenylate, binds appropriate tRNA molecules D arm and then the amino acid is transfered from aa-AMP to2' or 3'-OH of last tRNA nucleotide.
6. Sythetase also check wheather incorrect tRNA added, aminoacyl-tRNA bond is hydrolyzed or not.