tRNA molecules are loaded with their corresponding amino acids by enzymes called aminoacyl-tRNA synthetases.
Here's a breakdown of the process:
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Location: This process occurs in the cytoplasm of the cell.
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Enzyme Involvement: Each amino acid has a specific aminoacyl-tRNA synthetase that recognizes both the amino acid and its corresponding tRNA molecule(s). These enzymes are highly specific, ensuring the correct amino acid is attached to the correct tRNA.
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Two-Step Reaction: The aminoacylation process typically occurs in two steps:
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Activation of the Amino Acid: The amino acid reacts with ATP (adenosine triphosphate) to form an aminoacyl-AMP (adenosine monophosphate) intermediate, releasing pyrophosphate (PPi). This step requires the aminoacyl-tRNA synthetase enzyme.
Amino acid + ATP → Aminoacyl-AMP + PPi
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Transfer to tRNA: The aminoacyl-AMP then reacts with the appropriate tRNA. The amino acid is transferred to the 3' end of the tRNA molecule, specifically to the terminal adenosine residue. AMP is released.
Aminoacyl-AMP + tRNA → Aminoacyl-tRNA + AMP
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Aminoacyl-tRNA Formation (Charged tRNA): The resulting molecule is called an aminoacyl-tRNA, or charged tRNA. It's now ready to participate in translation. The tRNA is now "charged" with its specific amino acid.
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Anticodon Role: While the aminoacyl-tRNA synthetase recognizes the tRNA based on its overall structure, including the anticodon loop sequence, the attached amino acid is determined by the synthetase's specificity, not directly by the anticodon itself. The anticodon will later match the appropriate mRNA codon during translation.
In summary, aminoacyl-tRNA synthetases ensure that the correct amino acid is attached to its corresponding tRNA, forming an aminoacyl-tRNA which is then used during protein synthesis to add the correct amino acid to the growing polypeptide chain.
