amino acid charging of tRNA
Transfer RNAs bring the correct amino acid to the ribosome so that the amino acid can be added to the growing(nascent) polypeptide chain whose sequence is specified by the codons of the mRNA. In order for this to occur the correct amino acid must be covalently bonded to the appropriate amino acid. This is the job of the enzyme aminoacyl tRNA synthetase. For example, in the digram below a specific aminoacyl tRNA synthetase must bind a tRNA with the anticodon CCC and the amino acid glycine. The enzyme then forms a covalent bond between the carboxyl group of the amino acid and the hydroxyl groups of the pentose sugar of the tRNA. The aminoacyl tRNA synthetase recognizes the specific tRNA not because of the anticodon but because there are specific recognition sites on the tRNA.