18_CancerFinalized

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18 Cancer Mitosis Gone Wild
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18 Cancer Mitosis Gone Wild Click for Larger Image Unchecked cell growth results in tumors. The human body constantly uses cell division to make new cells. However, sometimes errors occur in this process and your body makes new cells that aren't needed. As these extra cells continue to divide, large masses known as tumors can form. While some tumors do not present a major threat to your body, others can invade and destroy tissues and organs eventually causing death. These tumors are called cancer. In this E-module we will address the following questions regarding cancer: 1. What causes uncontrolled growth/tumor formation? 2. How do tumor-causing mutations occur? 3. What is the difference between a benign and malignant tumor? 4. How do malignant tumors spread throughout the body? 5. How can you reduce your cancer risk? 6. What happens if you are diagnosed with cancer?
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Click for Larger Image Click for Larger Image Cancer can also be non tumorous, such as uncontrolled cell growth of white blood cells. This is known as leukemia (Shown Above). What causes uncontrolled growth/tumor formation? When a cell loses its ability to control its rate of cell division as a result of gene mutations , tumors occur. Recall that mutations are changes in the normal base sequence of DNA that either lead to changes in the protein encoded by that DNA or cause the protein to no longer be produced. Mutations in genes that affect cell division can lead to tumor formation. Typically a combination of at least 5 or 6 mutations in genes that control cell division must occur in a cell before a tumor forms. There are two major categories of genes that are involved in cell division. 1. Tumor Suppressor Genes Under normal conditions tumor suppressor genes function to control the rate of cell division. These genes stop cell division if an error has occurred. They also prevent cell division from occurring at times and in places where it is not required. If you think of uncontrolled cell division as a rapidly accelerating car, tumor suppressors would be the brakes. If a tumor suppressor gene mutates and the protein no longer functions correctly, that would be like having bad brakes with a slow reaction time. If a tumor suppressor gene mutates so that the protein is no longer produced, that would be as if one of your wheels was completely missing its brake. However, somatic cells have two copies of every gene, since in somatic cells there are two versions of every chromosome. Thus the rate of cell division will only increase when both copies of the gene mutate. When both copies of a tumor suppressor gene mutate, its as though your car has no brakes at all! Therefore, the important thing to remember about a tumor suppressor gene is that if its function is lost from both copies of the gene, the rate of cell division will increase. 2. Proto-Oncogenes.
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