The First Step in Translational Proofreading: Aminoacylation of tRNA by Aminoacyl-tRNA Synthetase

Translational proofreading is a critical process that ensures the accuracy of protein synthesis by minimizing errors during the translation of mRNA into polypeptides. The fidelity of translation depends on several quality control steps, with the first and crucial step being the aminoacylation of tRNA by aminoacyl-tRNA synthetase.

Understanding Translational Proofreading

• Translational proofreading refers to the mechanisms that verify the correct matching of amino acids to their corresponding tRNAs and the accurate decoding of mRNA codons by the ribosome.

• Errors in translation can lead to incorporation of incorrect amino acids, potentially resulting in dysfunctional proteins.

• Proofreading occurs at multiple stages: aminoacylation, codon-anticodon recognition, and peptide bond formation.

The First Step: Aminoacylation of tRNA

• Aminoacyl-tRNA synthetases (aaRS) are enzymes that charge tRNAs with their cognate amino acids, forming aminoacyl-tRNAs (aa-tRNAs).

• This aminoacylation is the first critical checkpoint in translational proofreading.

• aaRS enzymes have editing functions that hydrolyze incorrectly attached amino acids, ensuring high fidelity.

• Correct aminoacylation ensures that the tRNA carries the right amino acid corresponding to its anticodon.

Why Other Options Are Not the First Step

• Peptide bond formation (Option 2): Occurs later during elongation after the correct aa-tRNA has been delivered to the ribosome.

• Entry into A site (Option 3): The aa-tRNA enters the ribosomal A site after aminoacylation but is not the initial proofreading step.

• Formation of aminoacyl-tRNA, 40S ribosome, and mRNA ternary complex (Option 4): This is part of the initiation or elongation process but follows aminoacylation.

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• Translational proofreading

• Aminoacyl-tRNA synthetase accuracy

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• Ribosome A site decoding

• tRNA charging mechanism

• Translation accuracy checkpoints

• Amino acid-tRNA matching

• Translation initiation complex

• Peptide bond formation

Conclusion

The initial and most critical step in translational proofreading is the aminoacylation of tRNA by aminoacyl-tRNA synthetase. This process ensures that each tRNA is charged with the correct amino acid, setting the stage for accurate decoding and protein synthesis. Subsequent steps like entry into the ribosomal A site and peptide bond formation occur after this essential quality control checkpoint.

Correct answer: (1) Amino-acylation of t-RNA by amino acyl t-RNA synthetase