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

Question

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: (a) upon creation of the 70s initiation complex
(b) after an initial round of peptidyl transfer, prior to aminoacyl tRNA binding
(c) following aminoacyl tRNA binding, but before the peptidyl transfer reaction
(d) after peptidyl transfer, but before translocation is completed by EF-G
(e) in the presence of puromycin, prior to peptidyl transfer
(f) upon reaching a stop codon
(g) following release of the polypeptide chain, but before the appearance of RRF

Explanation / Answer

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

(a) upon creation of the 70s initiation complex

Initiation codon is place at the p site.

(b) after an initial round of peptidyl transfer, prior to aminoacyl tRNA binding

P site possess beginning of the peptide chain to be encoded and A site has next amino acid to be added to peptide chain.

(c) following aminoacyl tRNA binding, but before the peptidyl transfer reaction

The growing polypeptide attached to t RNA in the P site is detached from the tRNA in the P site. A peptide bond is formed between the last amino acid and to the amino acid still attached to the tRNA in the A site.

(d) after peptidyl transfer, but before translocation is completed by EF-G

Deacylated tRNA in the p site and dipeptidyl tRNA in the A site move to the E and P sites and a new codon moves into the A site.

(e) in the presence of puromycin, prior to peptidyl transfer

Puromycin (an antibiotic) is present in the A site, a growing peptide of P site links the puromycin with a peptide bond.

(f) upon reaching a stop codon

When a termination codon UAG,UGA,UAA moves into A site, termination occur. Protein formed is relased from the ribosome.

(g) following release of the polypeptide chain, but before the appearance of RRF

Ribosome recycling factor dissociates ribosome from mRNA after translation.

Before RRF, mRNA with termination codon is present at Asite, an uncharged tRNA at P site and an intact ribosome.

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