The Cell Anatomy and Physiology Practice Test

The main idea is how tRNA moves through the ribosome during protein synthesis: the A site is where the next amino acid-bearing tRNA enters, the P site holds the growing polypeptide on its tRNA, and the E site serves as the exit for the now-deacylated tRNA after it has donated its amino acid. That sequence is exactly what the description states: the A site accepts aminoacyl-tRNA, the P site holds the growing polypeptide, and the E site exits deacylated tRNA. The other descriptions mix up these roles—for example, placing the growing polypeptide in the A site, or saying the A site exits tRNA, which contradicts the flow of tRNA through the ribosome.