Question

In a reticulocyte lysate the polynucleotide 5'-AUGUUUUUUUUUUUUUUU directs the synthesis of Met-Phe-Phe-Phe-Phe. In the presence of farsomycin, a new antibiotic being developed, this polymer directs synthesis of Met-Phe only. From this information, which of the following deductions could you make about farsomycin?

a. It prevents formation of the 80S initiation complex, which contains the initiator tRNA and both ribosomal subunits
b. It inhibits binding of aminoacyl-tRNAs to the A site in the ribosome
c. It inactivates peptydil transferase activity of the large ribosome subunit
d. It blocks translocation of peptidyl-tRNA from the A site to the P site of the ribosome
e. It interferes with chain termination and release of the peptide

Answer 1

Farsomycin inhibits the inactivation of peptidyl transferase activity of the large ribosomal subunit.

Step-by-step explanation:

The information provided suggests that farsomycin inhibits the inactivation of peptidyl transferase activity of the large ribosomal subunit, thereby preventing the synthesis of additional amino acids in the polypeptide chain. This can be inferred from the fact that in the presence of farsomycin, the polymer 5'-AUGUUUUUUUUUUUUUUU only directs the synthesis of Met-Phe, instead of the complete sequence Met-Phe-Phe-Phe-Phe. Therefore, deduction (c) is the most likely inference that can be made about farsomycin.

Answer 2

Farsomycin most likely inhibits the binding of aminoacyl-tRNAs to the A site in the ribosome, as it allows the initiation of polypeptide synthesis but prevents its elongation beyond the addition of one amino acid.

Step-by-step explanation:

From the information provided about the antibiotic farsomycin and its effects on the synthesis of the polypeptide Met-Phe, it can be deduced that farsomycin possibly has a specific action on the ribosome. Given that polypeptide synthesis stops after Methionine (Met) and only one Phenylalanine (Phe) is added, option b, inhibit binding of aminoacyl-tRNAs to the A site in the ribosome, seems to be the correct action of farsomycin. This deduction is made as translation is initiated, but the elongation is halted after the addition of only one amino acid. This suggests that the antibiotic might be blocking subsequent aminoacyl-tRNA molecules from entering the A site, necessary for chain elongation.

Option a is unlikely because initiation does occur, option c is unlikely as at least one peptide bond is formed, option d is unlikely due to the same reasoning as option c, and option e refers to chain termination which is not where the process is halted in this scenario.