<Tr> <Th> PDBsum </Th> <Td> structure summary </Td> </Tr> <P> An aminoacyl - tRNA synthetase (aaRS or ARS), also called tRNA - ligase, 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 20 different types of aa - tRNA are made by the 20 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> <P> As genetic efficiency evolved in higher organisms, 13 new domains with no obvious association with the catalytic activity of aaRSs genes have been added . </P>

What type of rna has an amino acid attached and is used in the formation of a peptide chain