Answers must be written out in paragraph form. At the start of mitosis, sister chromatids are held together by a complex of proteins. Separase is an enzyme that cleaves the complex, enabling the chromatids to separate during mitosis. Separase is overexpressed in many cancer cells, and scientists hypothesized that they might be able to slow or stop the growth of cancer cells by blocking the activity of separase. The scientists found a compound they named Sepin‑1 that appears to effectively cleave and thus inactivate purified separase protein in vitro (in a test tube).

To test whether Sepin‑1 inhibits the growth of cancer cells, the scientists added increasing concentrations of Sepin‑1 to many different types of cancer cell lines growing in culture. A representative sample of the data they obtained is shown in Figure 1. The scientists also proposed to examine whether there is a relationship between the sensitivity of different types of cancer cells to Sepin-1, as measured by the concentration of Sepin-1 that caused 50% of the cells to die, and the relative concentration of separase in the different cell lines. A representative sample of the data is shown in Table 1

(a)identify the point in mitosis at which separase cleaves the protein complex that holds sister chromatid pairs together. In normal cells, separase is kept in an inactive state until it is needed. Explain how the progression of cells past sequential cell cycle checkpoints and the activity of enzymes such as separase is controlled by interactions between two major groups of regulatory proteins.

(b) Identify an independent variable in the experiment graphed in Figure 1. Based on the data in Figure 1, identify a control that shows that Sepin‑1 rather than something else in the culture medium is inhibiting the growth of the cancer cells.

(c) Based on the data in Table 1, describe the general relationship between the sensitivity of cells to Sepin‑1 and the concentration of separase in the cells. Use the Figure 1 data to calculate the ratio between the amount of Sepin‑1 required to kill 50% of the cells in the cell line that is most sensitive to the compound and the cell line that is least sensitive to the compound.

(d) The scientists hope to test Sepin‑1 in clinical trials with human cancer patients. The scientists claim that one way to test the efficacy of the Sepin‑1 treatment will be to obtain periodic samples of the patients’ cancer cells and determine the percent of cells in metaphase. Provide reasoning to support the scientists’ claim.