What is the function of aminoacyl-tRNA synthetases?

• A. They charge tRNAs with their correct amino acids
• B. They catalyze peptide bond formation
• C. They unwind mRNA
• D. They cap RNA

Answer: (A)

Aminoacyl-tRNA synthetases are the enzymes that attach the correct amino acid to its corresponding tRNA, a process called charging. They first recognize both the amino acid and the specific tRNA, then use ATP to activate the amino acid, forming aminoacyl-AMP. The enzyme then transfers the activated amino acid to the 3’ end of the tRNA, producing a charged tRNA that can deliver the amino acid to the ribosome during translation. This ensures that the codon in mRNA is matched with the correct amino acid in the growing polypeptide, maintaining genetic code fidelity. Some synthetases also have editing functions to proofread and remove mischarged amino acids, further reducing errors. In contrast, peptide bond formation is carried out by the ribosome’s peptidyl transferase, unwinding of mRNA is done by helicases, and RNA capping is a separate processing step for eukaryotic pre-mRNA.