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Q10 - Timing Cell-Cycle Phases with a Thymidine Pulse-Chase

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Cell Cycle, Mitosis & Meiosis

An experiment was set up to observe the cell cycle length of a strain of yeast. Activated yeast cells were subcultured into a new medium with an initial concentration of 10^6 cells/mL. After 40 h, the number of cells increased to 4 x 10^6 cells/mL. A portion of the culture was taken for a separate experiment. In this experiment, cells were incubated for 15 min in a medium containing radioactive thymidine before washing and re-growing on a new medium containing non-radioactive thymidine. Cell samples were then taken periodically to measure the percentage of mitotic cells containing radioactive thymidine. Fig.Q.10 shows the result obtained from the experiment. At each sampling, about 1% of the total cells sampled were undergoing mitosis.

Figure 1. Figure 1.

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

A. The synthesis rate of histone proteins is relatively high between 6 and 10 hours after radioactive labeled thymidine exposure.
B. S phase of the cell cycle takes about 5 hours.
C. M phase of the cell cycle takes longer than 1 hour.
D. Most of the radioactive thymidine is assimilated in the S phase of the cell cycle.
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Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)