tRNALadungen
tRNALadungen, or charged tRNA, are tRNA molecules that carry a covalently attached amino acid at their 3' terminus. They are the substrates used by ribosomes to synthesize proteins. Charged tRNAs are produced by a family of enzymes called aminoacyl-tRNA synthetases, one for each amino acid. The charging reaction proceeds in two steps: activation of the amino acid with ATP to form aminoacyl-AMP, followed by transfer of the amino acid from aminoacyl-AMP to the 3' end of the tRNA, yielding aminoacyl-tRNA and releasing AMP and pyrophosphate. The process requires magnesium ions and is energetically costly.
Fidelity is essential. Many synthetases possess an editing site that hydrolyzes mischarged tRNAs, and some organisms
In the cell, the pool of charged tRNA reflects amino acid availability and translation demand. During elongation,
Organisms maintain cytosolic and organellar (mitochondrial, chloroplast) sets of aminoacyl-tRNA synthetases, with organellar enzymes often specialized