Question

1.      tRNA aminoacylation

a.      What is aminoacylation? Where on the tRNA does it occur?

b.      Why is ATP required for aminoacylation? Why is the hydrolysis of PPi generated during aminoacylation important?

c.       What is the significance of the high-transfer potential of the ester bond created during tRNA aminoacylation?

d.      Why is the specificity of aminoacyl-tRNA synthetases important? How do these enzymes ensure their specificity?

e.      Are you familiar enough with amino acid side chains to answer questions about aminoacyl-tRNA synthetase specificity? (e.g. how might similar amino acids like valine, serine and threonine be distinguished?)

f.        Do you understand why there are differences in amino acid recognition between activation and editing sites? And how those differences dictate the specificity of the two different activities?

Answer 1

1.a. Aminoacylation is the term used for the joining of the correct amino acid on the tRNA. This attachent occurs in the presenceof enzymes called as aminoacyl-tRNA synthetases. The amino acids get attched to the anticodon site of tRNA.

b.The overall reactionfor the aminoacylation is

Amino acid+ ATP +RNA <--> aminoacyl-tRNA+AMP+PPi

The reacion requires ATP as pysophosphate is hydrolysed. This becomes a chain and drives other reactions.

c. The high transfer potential of ester bond is very important as aminoacytRNA are the active subtrates for the peptide bond formation in protein synthesis.

d. The specificty of aminoacyl-tRNA ase is very important as multiple tRNA's will usually have the same amino acids but different codons. But these enzymes ensure that the right amino acid attaches to the correct anticodon of tRNA.

But, under some conditions non-cognate amino acids will become charged resulting in misaminoacylated tRNA. These misaminoacylated tRNAS will hinder proper protein synthesis. Therefore in order to prevent incorrect protein synthesis, tRNAses are hydrolyzed by the aminoacyl tRNA synthetases.