Final answer:
To start the elongation phase of translation, charged tRNA binds to the A site of the ribosome. The ribosome moves along the mRNA, forming peptide bonds between amino acids and progressing the growing polypeptide chain through a series of transitions from A to P and to E sites, powered by GTP hydrolysis.
Step-by-step explanation:
To begin each round of elongation during translation in both prokaryotes and eukaryotes, charged tRNA, carrying the next amino acid to be added to the polypeptide chain, first binds to the A site of the ribosome. This step is crucial for elongation, as it ensures the correct sequential addition of amino acids to the growing polypeptide chain. After a peptide bond is formed between the amino acid at the A site and the growing polypeptide chain at the P site, the ribosome will transition or 'translocate', allowing the tRNA initially at the A site to move to the P site. The tRNA that was in the P site, now without an amino acid, moves to the E site before exiting the ribosome.
The ribosome moves along the mRNA strand in the 5' to 3' direction during translation, with elongation factors hydrolyzing GTP to provide the necessary energy for this process. Peptide bond formation involves the peptidyl transferase activity and is energy-dependent, relying on the high-energy bond between each amino acid and its tRNA. In E. coli, this rapid process can incorporate an amino acid in as little as 0.05 seconds, highlighting the efficiency of the protein synthesis machinery.