1. Many types of cancer are treated with a combination of therapies. In lung cancer, some tumors
respond well to the drug paclitaxel followed by radiation treatment. Paclitaxel is a chemical that
disrupts mitosis. Instead of spindle fibers originating from the two sides (poles) of the cell, paclitaxel-
treated cells develop three poles and then divide into three cells (tripolar division). Radiation therapy is
more effective on tumor cells that have undergone tripolar division than on cells that have undergone
normal mitosis.
Researchers treated cancer cells in the lab with different concentrations of paclitaxel for 15 hours. The
researchers then determined the average percent of mitotic cells that were tripolar. The results are
shown in Table 1.
Table 1. Effect of Paclitaxel concentration on percent of mitotic cells that were tripolar
Average Percent of Mitotic Cells
Concentration of Paclitaxel (nM)
that were Tripolar (USEX)
0
0.0 0.0
2
17.0+ 3.0
4
48.0 + 3.5
6
65.0 5.0
8
70.0 + 4.0
10
50.0+ 2.0
The AURKA gene encodes an enzyme that helps assemble the spindle fibers, which signals the cells to
continue through mitosis. When researchers analyzed the levels of AURKA protein in different types of
cancer cells, they found that cancer cells expressing high levels of AURKA protein had more tripolar
divisions when treated with paclitaxel, than did cancer cells expressing low levels of AURKA protein.
(a) Describe the situations in which a normal human cell would enter the cell cycle and undergo
mitotic cell division. Explain how spindle fibers help ensure the products of mitosis are two
identical cells with a full set of chromosomes.
(b) Using the template in the space provided for your response, construct an appropriately labeled
graph that represents the data shown in Table 1. Based on the data, determine the
concentration(s) of paclitaxel that is (are) most effective in causing tripolar cell division.
(c) Based on the data, identify the lowest level of paclitaxel that will allow for at least 50% of the cells
to be tripolar
(d) Predict the effect of a mutation that prevents the expression of AURKA on a normal
(noncancerous) cell.