Magic Bullets - Chemistry vs. Cancer

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    Cancer Detectives
    A Class Simulation

    General Safety Guidelines

    How can you study something that you cannot see? This is a major problem confronting many modern scientists. For chemists and biologists the problem is that the molecules being studied are so small that they cannot be seen directly. Even cells of the body are much too small to be seen easily. How then can scientists study them?

    In addition to his achievements in immunology and cancer chemotherapy, Paul Ehrlich discovered ways to stain cells using chemical dyes. He described a system of dyes that were either acidic, basic, or neutral. This system of staining cell tissue enabled scientists to see parts of cells that they might not otherwise be able to distinguish without staining. Today there are dozens of staining techniques as well as more advanced methods of seeing small objects.

    When cancer cells become numerous enough and group together, they may become visible to the naked eye, or visible under a microscope, as a tumor. Tumors may also be felt as small lumps. Groups of cancer cells that are not large enough to be seen by the naked eye or felt by touch sometimes can be seen by radiation imaging, X-rays, for example. Often, chemical or biological tests are needed to detect the cancer cells. It is interesting to note that the methods of detecting cancer are similar to the methods of treating cancer — surgery (sight and touch), radiation (imaging scans), and chemotherapy (chemical tests).

    In this exercise your lab group will take on the role of the scientist who works with cancer cells. Your first task is to try to detect cancer in just one or two "cells." Then, along with other lab groups in your class (your fellow scientists), you will determine the rate of occurrence of cancer in the entire population (your class).

    There are two types of paper "cells" in this exercise: normal cells and cancer cells. Your teacher will give each of you two of these cells. (Each person will not necessarily receive one of each type.) In the classroom there are more normal cells than cancer cells. By a series of careful observations you and your classmates should be able to identify which are the cancer cells.

    Materials

    • Paper "cells"
    • Ultraviolet light source
    • Cotton swabs
    • Iron(III) chloride solution

    Procedure

    To record your observations, print out this worksheet.

    A. Visual (naked eye) Detection

    1. Carefully observe and compare the two paper "cells" you have been given. Record your observations.

    2. Compare your cells and your observations of them with at least three other lab groups. Are all your cells alike? What characteristic(s) of the cells is (are) different?

    3. Within your lab group, propose a hypothesis that would allow you to distinguish a cancer cell from a normal cell. Your teacher will help you exchange ideas with classmates to reach a class consensus.

    4. Now test this hypothesis by determining if a new, unknown cell obtained from your teacher is normal or cancerous.

    5. Again, compare your results with other members of the class.

    B. Radiation (ultraviolet fluorescence) Detection

    1. Expose your cells to an ultraviolet light ("black" light). Observe each cell carefully for fluorescence (brightened areas). Caution: Do not look directly at the light source.

    2. Record your results on the data table.

    3. Do the new results affect the class hypothesis about distinguishing cancerous from noncancerous cells? If so, how?

    C. Chemical (color change) Detection

    1. Using the "developer" bottle containing iron(III) chloride solution and a cotton swab, spread a thin layer of this chemical across the area of the cell's nucleus. Observe carefully for any changes.

    2. Record your results on the data table.

    3. Do the new results affect the class hypothesis about distinguishing cancerous from noncancerous cells? If so, how?

    Follow-up Discussion

    Although this exercise simulated the detection of cancer cells, it is important to note that, in reality, scientists must actually see pieces of body tissue to make comparisons as you did here with single cells. Individual cells usually do not give scientists enough information upon which to judge whether or not they are cancerous. (Real cancer cells don't have such obvious marks as yours did in this lab.) Your teacher will help you collect class information about all the cells in the class. Add up the total number of cells in the class. How many of them are cancer cells? What percent of the total are cancer cells?

    Questions/Conclusions

    1. What three methods are used to detect cancer cells in this exercise?

    2. Which of the three methods appeared to be the most sensitive? The least sensitive?

    3. How did the class hypothesis about cancer cells change with the results of each new experiment?

    4. What new questions arise as a result of your work?

    Optional

    If you found any conflicting results, try to relate these conflicting findings to actual medical diagnoses.

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