Help Protein synthesis can be disrupted by the antibiotic erythromycin by preven
ID: 280208 • Letter: H
Question
Help Protein synthesis can be disrupted by the antibiotic erythromycin by preventing ribosomal translocation (move ment of the ribosome relative to the mRNA). It does not affect any other step in protein synthesis. ou are doing a translation reaction in vitro (i.e., in a test tube) and you add erythromycin just befo the 3d bond in the amino acid chain is about to be formed. You wait a few minutes to allow the reaction to proceed and then look at the ribosome. 4. Which tRNA will you find in the A site? a. b. c, d. tRNA #2 tRNA #3 tRNA #4 tRNA #5 5. The carboxyl end of AA#3 should now be bonded directly to a. tRNA #3 b. tRNA #4 C. AA #2 d. AA#4
Explanation / Answer
4. The A-site will have tRNA #3.
After the tRNA #3 carrying the 3rd amino acid is attached to the A site , the 3rd amino acid forms a peptide bond with the growing polypeptide chain in P site and the bonded chain is then transferred to the A site. After this translocation occurs which transfers the tRNA#3 from A-site to P site. As just before the bond formation the erythromycin is added, it stops the translocation and the tRNA#3 with the growing peptide chain remains at the A site.
5. The carboxylic end of AA#3 is bonded directly to tRNA #3.
Amino acids are attached to tRNAs by an ester bond with their carboxylic end. As the translation stops when the tRNA#3 is still in the A site and the growing peptide chain is joined to it via AA#3 which is joined with its carboxylic terminal end to the tRNA.
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