Which statement about the ribosome A, P, and E sites is correct?

• A. P site holds the growing polypeptide
• B. A site accepts aminoacyl-tRNA (correct)
• C. E site binds mRNA
• D. A site binds the ribosome to mRNA.

Answer: (B)

The key idea is how tRNA binding sites coordinate elongation during translation. The A site is the entry point for aminoacyl-tRNA, the charged tRNA that brings the next amino acid to be added and pairs with the codon on the mRNA. This placement is what allows the ribosome to read the genetic code and build the growing protein.

The P site, on the other hand, holds the tRNA that already carries the growing polypeptide chain; it’s where the chain is attached before the next amino acid is added. After a peptide bond forms, the chain shifts so the peptidyl-tRNA moves into the A site and the old tRNA moves into the E site to exit.

The E site is the exit site for uncharged or now-empty tRNA, not a place where mRNA binds. The ribosome–mRNA interaction occurs through the mRNA channel in the small subunit, not at the exit site. So the correct description is that the A site accepts aminoacyl-tRNA.