Question

2. The graphs below represent various curves obtained in different in vitro bacterial translation experiments in which a mixture of radioactive amino acids are added to a cell-free translation assay. The peptide product was assayed as counts per minute (cpm) that resulted from incorporation of a mixture of radiolabeled (radioactive) amino acids. The arrows represent the times at which various substances were added to the systems. (6 points) Cpm Cpm Cpm Cpm Time Time Time Time a) The addition of an antibiotic at the start of the assay results in the curve shown in graph III, while addition at a later time yields the curve shown in graph I. Which step in protein synthesis (translation) is this antibiotic most likely blocking? (2 points). b) Which graph (1-V) most likely depicts the addition of met-tRNA (methionine-tRNA) to a system that lacks only this component (2 points). c) Which graphs (I-V) most likely depicts the addition of an antibiotic that binds irreversibly to the A site of the ribosome? For this question, more than one choice may apply. Select all that apply (2 points).

Answer 1

A) this antibiotic mostaly blocking the initiation step of translation. As we can see in the graph III addition of antibiotic at initiation step inhibt the protein synthesis.

While in graph I antibiotic is added after initiation step, here it did not affect protein synthesis because initaion has already completed and after that antibiotic has been added so that's why it did not affect protein synthesis.

B) out of these graphs , Graph IV depicts this graph mentioned in the question.

As we can see inital protein synthesis is not present , but after addition of met tRNA , protein synthesis started.

C) addition of an antibiotic which bind to A site inhibits addiction of new amino acid in the chain. Thus amino acid numbers in chain will remain constant. Here graph II depicts this situation. Here after addition of antibiotic, no of amino acid is constant in peptide chain.