GENERAL BIOLOGY I ASSIGNMENT #4

Cancer is caused by mutations in the DNA that alter genes involved in cell growth. In some people, these mutations occur as a result of exposure to carcinogens in the environment.

Others inherit defective genes that cause cancer or make them more susceptible to developing cancer. Researchers interested in determining the cause of a certain inheritable form of cancer obtained cell samples from oncologists working with such patients.

These cell samples are called “study group.” As a control, the researchers obtained cell samples from people that do not have cancer and have no family history of cancer. These cells are called “normal.”

In this study, the two groups of cells were grown in normal cell culture conditions, then stained and examined under a microscope to determine the percentage of cells in each phase of the cell cycle.

Next, each culture was subjected to a carcinogen/mutagen (ultraviolet light) and allowed to grow. Cells were then stained and once again the percentage of cells in each phase was determined.

Examine the data in table 1. The proportion of cells in any phase is a measure of how long cells are spending in that phase.

Table 1

1. These results indicate that normal cells and study group cells respond to UV light differently. Summarize this difference.

In the first experiment, researchers were only able to distinguish cells in interphase from cells in mitosis. In the second experiment, the amount of DNA in each group of interphase cells was determined to distinguish cells in G1 from those in S or G2.

Cells in G2 have twice as much DNA as cells in G1 and although the amount of DNA in S phase depends on where the cells are in S phase, the average S phase cell has less DNA than G2 cells. Table 2 shows the results.

Only sperm have 1X DNA, so not surprisingly, no interphase cells are found with 1X. Cells in G1 and most of S phase would be grouped in the 2X category and cells from G2 thru cytokinesis in the 4X category.

Examine the data in table 2.

Table 2

2. What do these results indicate about the difference between normal and study group cells?

In their third experiment, researchers tested the viability of the cells. Cells were considered to be “viable” if they could complete two more mitotic divisions under normal culture conditions. Examine the data in table 3.

Table 3

3. Why are half of the study group cells exposed to UV light dying?

4. Considering the results of all three experiments, what process do you think is defective in the study group cells?

5. How could this defect lead to cancer?

Last Updated on November 9, 2022