The tRNA that is attached to the growing protein during translation is located in the P site (peptidyl site) of the ribosome. This tRNA, called the peptidyl-tRNA, holds the growing polypeptide chain. Meanwhile, a new aminoacyl-tRNA carrying the next amino acid binds to the A site (aminoacyl site) of the ribosome. The ribosome catalyzes the transfer of the growing polypeptide from the tRNA in the P site to the amino acid on the tRNA in the A site, extending the protein chain. After the peptide bond forms, the tRNAs shift positions, and the tRNA that was in the P site moves to the E site (exit site) before leaving the ribosome

. In summary:

• The tRNA attached to the growing protein is in the P site of the ribosome.
• The next aminoacyl-tRNA enters the A site.
• The peptide bond forms between the polypeptide on the P site tRNA and the amino acid on the A site tRNA.
• The tRNA in the P site then moves to the E site and exits the ribosome