Final answer:
During translation, a tRNA with a single amino acid attached binds at the A site, a tRNA with a polypeptide chain attaches at the P site, and a tRNA without an amino acid, ready to exit, is found at the E site.
Step-by-step explanation:
In the context of ribosomal sites during the process of translation in protein synthesis, the roles of the A site, P site, and E site are distinct:
- The A (aminoacyl) site is where incoming charged tRNAs bind. A charged tRNA is one that has an amino acid attached to it. This site is where the tRNA with a single amino acid attached would be initially found.
- The P (peptidyl) site binds charged tRNAs carrying amino acids that are already part of the growing polypeptide chain. Therefore, a tRNA with a polypeptide attached to it would mainly be found at this site.
- Lastly, the E (exit) site is where dissociated tRNAs are released after they have donated their amino acid to the polypeptide chain. A tRNA without an amino acid, ready to exit the ribosome, would be found here.
The process of translation elongation is indeed rapid, with E. coli's apparatus capable of adding each amino acid to the growing chain in merely 0.05 seconds.