During translocation, from which site is the unbound tRNA expelled, and into which site does the peptidyl-tRNA move?

During translocation, from which site is the unbound tRNA expelled, and into which site does the peptidyl-tRNA move?

• A. P site; A site
• B. A site; E site
• C. E site; A site
• D. E site; P site

Answer: (D)

During elongation, tRNAs move through the three ribosomal sites in a coordinated way. After the new aminoacyl-tRNA in the A site donates its amino acid to the growing peptide in the P site, the tRNA that was in the P site becomes uncharged and slides into the E site, where it exits the ribosome. Meanwhile, the tRNA that was in the A site, now carrying the nascent peptide, moves into the P site. This translocation resets the A site for the next aminoacyl-tRNA and leaves the E site to receive the next uncharged tRNA.

During elongation, tRNAs move through the three ribosomal sites in a coordinated way. After the new aminoacyl-tRNA in the A site donates its amino acid to the growing peptide in the P site, the tRNA that was in the P site becomes uncharged and slides into the E site, where it exits the ribosome. Meanwhile, the tRNA that was in the A site, now carrying the nascent peptide, moves into the P site. This translocation resets the A site for the next aminoacyl-tRNA and leaves the E site to receive the next uncharged tRNA.