3. Describe the A, P, and E sites of the ribosome. Where are they located? What

Question

3. Describe the A, P, and E sites of the ribosome. Where are they located? What occupies each of the sites during the following stages of translation:

Example. upon creation of the 70s initiation complex Answer: A, E sites empty, P site containing fMet-tRNAi fMet

a. after an initial round of peptidyl transfer, prior to aminoacyl tRNA binding

b. following aminoacyl tRNA binding, but before the peptidyl transfer reaction

c. after peptidyl transfer, but before translocation is completed by EF-G

d. following release of the polypeptide chain, but before the appearance of RRF

Explanation / Answer

The ribosome has three active sites: the A site, the P site, and the E site. The A site is the point of entry for the aminoacyl tRNA (except for the first aminoacyl tRNA, which enters at the P site). P site is jointly contributed by the two ribosomal unit. A and E site are the part of larger subunits. The first aminoacyl t -RNA complex binds to P site. During elongation the aminoacyl t RNA complex reaches theA site and next amino acid is attached to A site.And the E site which is the exit site of the now uncharged tRNA after it gives its amino acid to the growing peptide chain. (A.) Prior to aminoacyl t RNA binding A, E sites empty, P site carries f- met RNA. (B.) A site carries aminoacyl t RNA,E site is empty.( C) peptidyl t RNA complex reaches to P site and A site free.

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