Chapter 8: Cell Division

1.	What is the fundamental difference between mitosis and meiosis? [Hint]
2.	Mitotic spindle fibers are composed of [Hint]
3.	Taxol is a drug that stabilizes microtubules and prevents them from depolymerizing. Consequently, treated cells fail to complete mitosis. At which phase of mitosis are cells treated with taxol likely to arrest? [Hint]
4.	During mitosis, it is necessary for the nuclear envelope of the parent cell to dissolve. This is accomplished, at least in part, by phosphorylation of proteins associated with the nuclear envelope. If the enzyme responsible for that phosphorylation event is inhibited, at which phase of mitosis are cells likely to arrest? [Hint]
5.	In addition to a pulse-labeling experiment, the length of the different phases of the cell cycle can also be measured by labeling cells continuously with radioactive thymine and waiting to see how long it takes for radioactivity to appear in metaphase chromosomes. What phase of the cell cycle would be represented by the time between the addition of radioactive thymine and the time at which radioactivity first appears in metaphase chromosomes? [Hint]
6.	The length of the different phases of the cell cycle can be measured by labeling cells continuously with radioactive thymine and waiting to see how long it takes for radioactivity to appear in metaphase chromosomes. After the radioactivity first arrives in metaphase, it is noticed that the amount of radioactivity in metaphase chromosomes increases steadily over several hours and then reaches a plateau. What phase of the cell cycle would be represented by the time between the first arrival of radioactive thymine in metaphase and the time at which the radioactivity reaches a plateau? [Hint]
7.	Although the process of chromosome partitioning during mitosis is visible through the light microscope, the process of DNA replication is not. Why? [Hint]
8.	A certain species of animal has six pairs of chromosomes. How many molecules of DNA do the nuclei of these animals have during G2 phase? [Hint]
9.	Much of what is known about the function of cyclin and Cdk was learned by mutations in yeast. One yeast mutant is known as Wee1. As its name implies, this yeast mutant never achieves full size. It divides continuously without allowing time for the cells to grow to their normal size. The defect causes inactivation of a gene that encodes a protein kinase. What might be a possible role for this kinase in normal wild-type yeast? [Hint]
10.	One of the interesting experiments conducted with frog oocytes revealed that with an appropriate stimulus, the cyclic appearance and disappearance of cyclin occurs even in the absence of a nucleus. What does that imply about the production of cyclin in oocytes during mitosis? [Hint]
11.	Some of the earliest experiments in the control of the cell cycle were the cell fusion experiments of Rao and Johnson. Fusion of cells in M phase with cells in interphase caused the nuclei from the interphase cells to behave as if they were in mitosis. These results could have been obtained by adding just a part of the M phase cells to the interphase cells. What portion of the M phase cell would suffice to cause the interphase nuclei to mimic the process of mitosis? [Hint]
12.	When G2 cells were fused with S phase cells, the G2 cells did not try to replicate their DNA. What does that result imply? [Hint]
13.	What would have been the effect on interphase frog oocytes if chromosomes from M phase oocytes were injected into them? [Hint]
14.	What would be the consequence of inhibiting the enzyme that degrades mitotic cyclin? [Hint]
15.	What would be the consequence of inactivation of E2F? [Hint]
16.	Many anticancer agents used therapeutically work by interfering with DNA replication. This could lead to badly mutated daughter cells following mitosis. Nevertheless, the treatment usually results instead in a failure of the cells to divide. Why might this be? [Hint]
17.	One of the causes of cancer is mutation of the genes that encode for proteins in the biochemical pathway regulated by PDGF. How could such mutations cause cancer? [Hint]
18.	Which of the following alterations of the Rb gene will cause cancer? [Hint]
19.	What is the critical event during anaphase that can help prevent cancer? [Hint]
20.	A double pulse-chase experiment has been used to determine whether the replication of DNA in mitochondria is synchronized with the cell cycle or independent of it. Growing cells were pulse-labeled with radioactive thymine. At different periods of time after the pulse, cells were labeled again with a heavy analog of thymine. DNA replicating during the time of labeling with heavy thymine was therefore heavier than its unlabeled counterpart. Mitochondria were isolated from each sample shortly after the labeling with heavy thymine, heavy chromosomes were separated from light chromosomes, and the heavy chromosomes were tested for radioactivity. What result would you expect if the mitochondria divided randomly relative to mitosis? [Hint]
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