Part A

Instructions: Questions 1-4 are based on the data shown below.

Handout Credit: Biology of Cells, www.BioInteractive.org

Caption: Relationship between the risk of cancer and the number of times stem cells divide in different types of body tissue over the course of a person’s lifetime. Lifetime risk (y-axis) is expressed as the base 10 logarithm of the probability of developing cancer, where 10-1 is 10% risk, 10-2 is 1% risk, and so forth.

BACKGROUND INFORMATION

Cancer is typically attributed to hereditary and environmental factors, but these only explain a fraction of overall cancer risks. These factors fail to explain why some of the body’s tissue types are more likely to develop cancer even in cases where hereditary and environmental risks are equal. For example, tissues of the small and large intestine are both susceptible to cancer caused by mutations in the APC gene, which regulates the production of the APC protein, a tumor suppressor that keeps cells from dividing in an uncontrolled way. The small and large intestines are presumably exposed to the same environmental factors, and yet cancer of the colon (part of the large intestine) is far more common than cancer of the duodenum (part of the small intestine). In this study, researchers investigated how a third factor – chance genetic mutations that occur during stem cell division – may contribute to the overall rate of cancer incidence in each tissue. The researchers plotted data from previously published studies to determine whether tissues with a greater number of stem cell divisions (and therefore a greater amount of DNA replication!) over a person’s lifetime is related to the overall risk of cancer in that tissue.

Questions:

1. What do the trends in this figure tell you about the relationship between stem cell divisions and cancer? 2 pts
2. What is a possible explanation/hypothesis for the difference in lifetime risk of colorectal cancer versus duodenal cancer (not the familial adenomatous polyposis (FAP) versions)? 2 pts
3. Why do you think researchers focused on stem cells rather than fully differentiated cells? 2 pts
4. Explain why the lung cancer (smokers) and lung cancer (non-smokers) data points are vertically aligned. 2 pts

Part B:

Terms in the Word Bank may help prime your thinking, but you are not required or limited by the terms listed.

Word Bank: Ras, P53, Rb, receptor tyrosine kinase, matrix metalloproteases

5- Describe how a mutation of a specific gene or an alteration to the DNA can contribute to cancer. Make sure to specify what the gene is, what type of mutation or DNA-altering mechanism is involved (e.g., activating/gain of function mutation, inhibiting/loss of function mutation), and how the alteration affects a particular cellular process. 3 pts (1 pt for each part that needs to be specified)

6- In order for cancer cells to leave their tissue of origin and invade neighboring tissues and to metastasize, the extracellular matrix may be ___________ by cancer cells with the action of _______. (Fill in the answer, 3 pts total-1.5 pts for process identified, 1.5 pts for type of protein identified).

7- List a hallmark of cancer (1 pt):