1. You have just read a paper that the addition of caffeine to cells disrupts the DNA damage checkpoint and you would like to understand why. By searching for proteins that bind to caffeine, you isolate a protein, Caf1. You believe that Caf1 is involved in the DNA damage checkpoint because when you delete Caf1 from yeast cells and add a drug that causes DNA damage, the cells fail to arrest in the cell cycle.
You give your Caf1-deleted cells to an undergraduate in the laboratory and ask him to take care of the strain for you while you take the weekend off to celebrate your finding. Upon your return, you find the poor undergraduate in tears. He explains that he thinks that he messed up the Caf1 mutant strain while you were gone because after growing Caf1 and wild-type cells in rich media and examining them during mitosis, Caf1 mutants looked the same as wild-type cells. Are you concerned about the undergraduate student’s findings? Why?

2. You are interested in epithelial tissue formation and work in a lab studying Madin-Darby canine kidney (MDCK) cells. MDCK cells spontaneously form hollow epithelial vesicles. Staining these vesicles with an anti-actin antibody demonstrates the existence of apical microvilli near the central cavity of the vesicle. A new postdoctoral fellow in the lab comes to you in a panic. You had given her some dissociated MDCK cells that have been cultured as single cells in a collagen matrix. Because the cells did not look obviously polarized to her, she stained the dissociated MDCK cells to visualize the microvilli and she does not see any signs of polarized microvilli localization in these cells. Explain why you are confident that you did not give her the wrong cell line, and suggest a better experiment that will allow her to test whether the cells you gave her are MDCK cells.