How many tRNA binding sites are inside a ribosome?

• A. 4
• B. 3
• C. 2
• D. 1

Answer: (B)

The ribosome has three tRNA binding pockets: the aminoacyl site for the incoming charged tRNA, the peptidyl site where the growing polypeptide is held and peptide bond formation occurs, and the exit site where the spent tRNA leaves. During elongation, one tRNA occupies the aminoacyl site and another occupies the peptidyl site, while the previously used tRNA moves to the exit site to depart. This arrangement provides space for both the incoming tRNA and the expanding polypeptide, plus a route for tRNA release, so three sites are needed and make sense biologically. That’s why the correct count is three.