Q4 - Pulse-Chase RNA Processing

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Pulse-chase experiments performed in cells are experiments in which cells are first exposed to labelled precursors of specific molecules for a short period of time (the pulse), unincorporated labelled precursors are then washed away, and presence of label in molecules of interest are followed through time (the chase). In an experiment designed to study gene expression, cells were exposed to labelled UTP during the pulse, and results of the chase part of the experiment are summarized in the figure below.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Based on the data presented, most (~90% of mass) of RNA that is synthesized in the nucleus is degraded in the nucleus without ever entering the cytoplasm.

B. Based on data presented, the complexity of RNA (which refers to number of different sequences) in the nucleus is higher than in the cytoplasm.

C. Assuming that introns constitute 60% of primary transcripts, splicing can account for the observed difference in amount of label in the nucleus at start of chase and amount of label in the cytoplasm after eight hours of chase.

D. It is expected that chases of longer than 8 hours would have ultimately shown a much higher amount of label in the cytoplasm than seen at 8 hours.

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Question reproduced from IBO 2018, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)