Final answer:
The process of shifting the chain back to the P site for a new tRNA to enter the A site during protein synthesis is called translocation, a part of the elongation phase of translation.
Step-by-step explanation:
The process mentioned in the question, where the chain is shifted back to the P site so that another tRNA can come into the A site and continue the translation process, is known as translocation. This is a critical part of the elongation phase of translation. During elongation, a charged tRNA initially binds to the A site, and then a peptide bond forms, connecting the amino acid from the tRNA at the A site to the growing polypeptide chain attached to the tRNA in the P site. Once this bond is formed, the ribosome moves along the mRNA, and the tRNA in the A site, now carrying the polypeptide, shifts to the P site. The empty tRNA in the P site moves to the E site for removal from the ribosome. This process allows a new charged tRNA to enter the A site and the sequence to continue, adding amino acids to the growing chain.