Final answer:
During protein synthesis elongation, aa-tRNA binds to the A site of the ribosome in a sequence of steps involving elongation factors, GTP hydrolysis, and peptidyl transferase activity, culminating in peptide bond formation and advancement of the ribosome along mRNA.
Step-by-step explanation:
The process of elongation within protein synthesis involves several key steps and essential factors. Specifically, during elongation, charged tRNA (aa-tRNA) binds to the ribosome's A site. Here are the steps in detail:
- A charged aminoacyl-tRNA (aa-tRNA) carrying the appropriate anticodon and its corresponding amino acid approaches the A site of the ribosome.
- The elongation factor Tu (EF-Tu) bound to GTP assists the aa-tRNA to enter the A site based on the codon-anticodon matching with the mRNA.
- GTP is hydrolyzed to GDP, releasing the EF-Tu and allowing the aa-tRNA to fully settle into the A site.
- Peptidyl transferase, a component of the large ribosomal subunit, catalyzes the formation of a peptide bond between the carboxyl end of the amino acid at the P site and the amino group of the new amino acid at the A site.
- The ribosome then undergoes a conformational change which translationaly moves or 'steps' the ribosome along the mRNA by three bases in the 3' direction.
- This translocation shifts the tRNA from the A site to the P site, and the tRNA that was in the P site moves to the E site to exit, thus allowing the A site to receive a new aa-tRNA.
In summary, the aa-tRNA binding to the A site is a complex process facilitated by elongation factors and GTP hydrolysis, leading to peptide bond formation and the growth of the polypeptide chain.