Amino acids are transferred to tRNA in a two-step process catalyzed by aminoacyl-tRNA synthetases (aaRSs).
The Two-Step Process of Aminoacylation
The process, known as aminoacylation or tRNA charging, ensures that the correct amino acid is attached to its corresponding tRNA molecule, a crucial step in protein synthesis. It proceeds as follows:
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Amino Acid Activation:
- The amino acid reacts with ATP (adenosine triphosphate) to form an aminoacyl-adenylate (aa-AMP).
- This reaction releases pyrophosphate (PPi), which is then hydrolyzed to inorganic phosphate (Pi), making the reaction irreversible and driving the overall process forward.
- The aminoacyl-adenylate remains bound to the aminoacyl-tRNA synthetase enzyme.
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tRNA Charging:
- The activated amino acid (aa) is transferred from the aminoacyl-adenylate to the 3' terminal adenosine of the correct tRNA molecule.
- Specifically, the amino acid's carboxyl group forms an ester bond with either the 2'-OH or 3'-OH group of the terminal adenosine. The specific hydroxyl group used can vary depending on the aaRS.
- This creates a charged tRNA, also known as aminoacyl-tRNA (aa-tRNA).
- The aminoacyl-tRNA is then released from the aminoacyl-tRNA synthetase enzyme, ready to participate in protein synthesis.
In summary, the aminoacyl-tRNA synthetases play a vital role in maintaining the fidelity of protein synthesis by ensuring the correct matching of amino acids and their respective tRNAs. Without the correct tRNA charging, the genetic code would be misread, leading to non-functional proteins.
