Question

You are given a flask with standard liquid media containing a population of S. pombe cells that have a temperature sensitive mutation of a gene that causes complete loss of function of the gene product at the restrictive temperature. The flask had been incubating at the permissive temperature in the dark before it was given to you, and the cells in the flask were replicating asynchronously with respect to the stage of the cell cycle. The mutated gene in this strain of yeast encodes an essential component of a UV-mediated DNA damage checkpoint. Which FACS plot (see attached figure) best represents how cells in this flask would appear following growth for 30 min at the restrictive temperature ? (Note, assume that FACS plot #1 shows analysis of a population of S. pombe replicating asynchronously (i.e. each cell within a population is at a random stage of the cell cycle) in culture. In the rich media assume the yeast have a cell cycle time of 100 min, with G1=50 min; S = 25 min; G2 = 15 min and M = 10 min).a. #2 b. #3 c. #4 d. #5 e. #6

Answer 1

The best graphic that represent the growth of the cells is the plot #2

Step-by-step explanation:

Using flow cytometry, a cell cycle analysis study uses a dye for DNA binding, and it is fluorescently labeled to allow stoichiometry of DNA to bind to DNA content.

During the phases, the DNA content will be:

G0 / G1 phase = 2n (diploid).

Phase S = 2n (duplication of DNA content)

G2 / M phase = 4n (content of tetraploid DNA 4n)

When cells are growing, a mutation will occur in the gene. This would lead to the cell cycle being unlikely to stop due to the checkpoint gene mutation, causing it to be unable to detect any damage. the cell cycle continues normally.

In exercise, cells that were in the G1 phase will reach the S phase. Therefore, the peak of that phase will be increased, and the peak of the G1 phase will decrease. The cells that were in the S phase will go to the G2 / M phase, which will increase the peak.