Question

As a ribosome translocates along an mRNA molecule by one codon, which of the following occurs? a. The polypeptide enters the E site. b. The tRNA that was in the A site departs from the ribosome via a tunnel. c. The tRNA that was in the P site moves into the A site. d. The tRNA that was in the A site moves to the E site and is released. e. The tRNA that was in the A site moves into the P site.

Answer 1

Answer:

e. The tRNA that was in the A site moves into the P site.

Explanation:

Translation comprises 3 steps :

1) Translation initiation

2) Translation elongation

3) Translation termination

Translocation step is a part of translation elongation step which is followed by the peptidyl transferase activity of ribosome. Due to the peptidyl transferase activity of ribosome, the N terminal of newly entered amino acid (amino acid attached with tRNA i.e. aminoacyl tRNA or charged tRNA) at 'A site' attacks the C terminus of amino acid which is already present in the 'P site' of complex and amide bond is formed between amino acids leading to elongation of peptide chain. Then after, the uncharged tRNA which is present in the 'P site' is expelled out the complex via 'E site' while the tRNA that was in 'A site' moves into the 'P site'.