Final answer:
The A (aminoacyl) site of the ribosome is where new charged tRNAs enter during translation elongation. As the ribosome translocates along mRNA, peptide bonds form, extending the polypeptide chain. This process, particularly rapid in bacteria like E. coli, involves precise movements of tRNAs between the ribosomal A, P, and E sites.
Step-by-step explanation:
The site where every new tRNA (transfer RNA) enters the ribosome is called the A (aminoacyl) site. This site is a functional site within the large ribosomal subunit that binds incoming charged aminoacyl tRNAs during the process of translation. The translation process can be divided into three steps: initiation, elongation, and termination. During elongation, as the ribosome moves along the mRNA, new tRNAs carrying amino acids enter the A-site. Peptide bonds are then formed between the amino acid at the A-site tRNA and the carboxyl group of the amino acid attached to the P-site tRNA, elongating the polypeptide chain.
Translocation is another critical step in this process, where the ribosome moves one codon at a time. After a peptide bond is formed, the tRNA at the P (peptidyl) site moves into the E (exit) site, and the A-site tRNA, now attached to the growing polypeptide chain, shifts to the P site. This movement makes the A site available again for the next charged tRNA to enter and continue the protein synthesis. Amazingly, in organisms like E. coli, this elongation process occurs incredibly quickly, with a rate of adding each amino acid in as little as 0.05 seconds.