<Tr> <Th> PDB </Th> <Td> RCSB PDB; PDBe; PDBj </Td> </Tr> <Tr> <Th> PDBsum </Th> <Td> structure summary </Td> </Tr> <P> An aminoacyl tRNA synthetase (aaRS) is an enzyme that attaches the appropriate amino acid onto its tRNA . It does so by catalyzing the esterification of a specific cognate amino acid or its precursor to one of all its compatible cognate tRNAs to form an aminoacyl - tRNA . In humans, the 21 different types of aa - tRNA are made by the 21 different aminoacyl - tRNA synthetases, one for each amino acid of the genetic code . </P> <P> This is sometimes called "charging" or "loading" the tRNA with the amino acid . Once the tRNA is charged, a ribosome can transfer the amino acid from the tRNA onto a growing peptide, according to the genetic code . Aminoacyl tRNA therefore plays an important role in RNA translation, the expression of genes to create proteins . </P>

Where is the amino-acid binding site located on the trna molecule