Question

When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following sets of structures would you be able to isolate from the cell?

Answer 1

The options are:

A) an assembled ribosome with a polypeptide attached to the tRNA in the P site

B) separated ribosomal subunits, a polypeptide, and free tRNA

C) an assembled ribosome with a separated polypeptide

D) separated ribosomal subunits with a polypeptide attached to the tRNA

E) a cell with fewer ribosomes

Answer:

The correct answer is A) an assembled ribosome with a polypeptide attached to the tRNA in the P site.

Explanation:

There are three sites in a ribosome E, P, and A. From A site aminoacyl tRNA enters the ribosome. When this tRNA shifts to P site the amino acids which were attached to the tRNA that was at P place shifts to a new tRNA molecule that replaced the old one.

The old deacylated tRNA leaves the mRNA-ribosome complex from E- site. So when translation reaction was to be experimentally stopped and there is no corresponding tRNA enters the A site then only an assembled ribosome with polypeptide chain attached to tRNA in P site can isolate from the cell because no tRNA is present at E and A site.