Question

Which among the following options regarding protein synthesis is/are correct?

• A. Uncharged amino acids are picked up by tRNA molecules randomly from the cytoplasm and are incorporated into the peptide
• B. Unprocessed mRNA is translated into the peptide in eukaryotes
• C. Most of the aminoacyl tRNA synthetase contains editing sites in addition to the acylation site
• D. Proteins are synthesised in the nucleus and then transported to the cytoplasm for their processing

Answer 1

The correct option is C Most of the aminoacyl tRNA synthetase contains editing sites in addition to the acylation site

Aminoacyl tRNA synthetase is an enzyme that loads the individual amino acids onto the tRNA to catalyse the aminoacylation of tRNAs. This enzyme plays a crucial role in protein synthesis by linking the amino acids to their cognate tRNAs. The enzymatic action proceeds in two steps-
First, in presence of ATP, an amino acid combines with its specific aminoacyl-tRNA synthetase producing an amino-acy;-adenylate-enzyme complex and release of the pyrophosphate (PPi) occurs.
Second, this complex reacts with tRNA specific for the amino acid to form amino-acyl-tRNA complex. tRNA complexed with amino acid is called charged tRNA.

Most aminoacyl tRNA synthetases contain editing sites in addition to the acylation sites. This double sieves the process and ensures a very high fidelity of the polypeptide. Generally, the acylation site rejects the amino acids that are larger than the correct ones and the hydrolytic site cleaves the species that are smaller than the correct ones preventing the incorrect incorporation of amino acid onto the tRNA; which greatly enhances the accuracy of the translation.


Eukaryotic mRNAs are processed by 5’capping, polyadenylation, removal of introns i.e., splicing and reconnecting of exons etc. before they are transported to the cytoplasm, where the process of translation occurs.