74. A study is done on a mammalian cell line that has a doubling time of 24 hours. These cells are  synchronized in G1 and then labeled for 2 days with BrdU (an analog of thymidine that increases  the density of DNA into which it is incorporated). At the end of the labeling period, chromosomal  DNA is isolated from the cells and its density analyzed by equilibrium centrifugation in cesium  chloride gradients. Which of the following patterns would be expected to be seen? (H=heavy,  L=light) a. 100% H/H b. 111% H/L c. 50% H/H, 50% H/L d. 50% H/H, 50% L/L e. 25% H/H, 50% H/L, 25% L/L   78. Diarrhetic shellfish poisoning is caused by okadaic acid. Dr. Mollusca finds that okadaic acid  increases the phosphorylation of Cl- channels in intestinal epithelial cells, causing the channels to  open. Dr. Mollusca concludes that okadaic acid activates a kinase that phosphorylates the Clchannels. Based on the given evidence, do you agree or disagree with Dr. Mollusca’s conclusion, and why? a. Agree, it is the most obvious conclusion and based on evidence of increased  phosphorylation. b. Disagree, since kinases do not phosphorylate Cl- channels. c. Disagree, because it is more likely that okadaic acid inhibits a phosphatase. d. Disagree, because based on the evidence you can’t conclude which enzyme is being  affected by the okadaic acid

74. A study is done on a mammalian cell line that has a doubling time of 24 hours. These cells are 
synchronized in G1 and then labeled for 2 days with BrdU (an analog of thymidine that increases 
the density of DNA into which it is incorporated). At the end of the labeling period, chromosomal 
DNA is isolated from the cells and its density analyzed by equilibrium centrifugation in cesium 
chloride gradients. Which of the following patterns would be expected to be seen? (H=heavy, 
L=light)
a. 100% H/H
b. 111% H/L
c. 50% H/H, 50% H/L
d. 50% H/H, 50% L/L
e. 25% H/H, 50% H/L, 25% L/L

78. Diarrhetic shellfish poisoning is caused by okadaic acid. Dr. Mollusca finds that okadaic acid 
increases the phosphorylation of Cl- channels in intestinal epithelial cells, causing the channels to 
open. Dr. Mollusca concludes that okadaic acid activates a kinase that phosphorylates the Clchannels. Based on the given evidence, do you agree or disagree with Dr. Mollusca’s conclusion,
and why?
a. Agree, it is the most obvious conclusion and based on evidence of increased 
phosphorylation.
b. Disagree, since kinases do not phosphorylate Cl- channels.
c. Disagree, because it is more likely that okadaic acid inhibits a phosphatase.
d. Disagree, because based on the evidence you can’t conclude which enzyme is being 
affected by the okadaic acid