Suggested answers to study guide #3
" Genes, Cell Division, Cancer and the Environment" Lecture on 2/6/01 (notes on Web page)
1. What do all types of cancer have in common?
A: All cancers involve an uncontrolled division of cells. Other characteristics may include loss of ability to attach to other cells.
2. What is the difference between a benign and a malignant tumor?
A: Benign tumors are slow growing and localized whereas malignant tumors usually grow more quickly and tend to invade other tissues.
3. What are carcinogens?
A: Carcinogens are cancer producing substances. This includes various chemicals and radiation.
4. What is meant by metastasis?
A: Metastasis technically means the shifting of disease from one part of the body to another. In the case of cancer, this is the stage during which the cancer spreads.
5. What are oncogenes and proto-oncogenes and what is the relationship between the two?
A: Our book states that oncogenes are genes that cause cancer (although the true definition is a little different). Proto-oncogenes are “normal” genes that have some “helpful” function in the body. When these genes become mutated they can become oncogenes.
6. If you inherit a cancerous gene, will you eventually get cancer? Explain why or why not.
A: No, since cancer requires more than one cancerous gene, inheriting such a gene would only increase your odds of developing cancer.
7. Give one reason why cancer may be caused by events that happened years beforehand.
A: Similarly to the answer in #7, you may have been exposed to a carcinogen years beforehand and that carcinogen activated a cancer gene. Since you need more than one cancerous gene in order to get cancer, the cancer only develops at a later time when all of the necessary cancer genes are present. And even though the latest event “caused” the cancer to develop, so did the event that occurred years beforehand.
8. List three types of skin cancer. Which of these is the most dangerous? What are some environmental factors that lead to skin cancer?
A: Melanoma, basal-cell carcinoma and squamous-cell carcinoma. Melanoma is the most dangerous and the depletion of the ozone is an environmental condition thought to contribute to skin cancers. With ozone depletion more carcinogenic cosmic rays can reach your skin.
9. If you are exposed to carcinogens and develop a cancerous gene, will that gene be passed on to your children? Why or why not?
A: Only if that cancerous gene developed in your sperm or ova. Your genes are passed onto your progeny through these cells; hence, only mutations in these cells could be passed onto your children.
10. Make two lists, one describing a few environmental aspects associated with cancer and one describing some behaviors associated with cancer.
A: We look forward to reading your lists.
11. Write down one thing you don’t know, but would like to know about cancer.
A: We will take all your questions and attempt to provide you with possible answers.
12. There was no workshop associated with this week’s biology, so there is no need to turn one in. However, make sure you have turned in all of your biology assignments to ensure your 4 biology credits.
Upper Division Questions:
For more information about cancer and telomeres check out http://www.sciam.com/0996issue/0996weinberg.html (it's a little old but it's fairly easy to understand and gives a great overview of it, and the more recent information online about cancer research often requires a paid subscription to actually read the articles).
13. What are telomeres? What is the relationship between telomerase and aging?
A: Telomeres are sections of DNA on the ends of chromosomes that consist of specialized repeated sequences of DNA (TTAGGG in humans). In the absence of telomerase, telomeres shorten with each cell division. Eventually, cells stop dividing when they sense that their telomeres are too short to maintain chromosomal integrity. In other words, telomeres can determine the lifespan of cells. The enzyme telomerase maintains telomere length by adding nucleotides one at a time to existing chromosomal ends in a regulated fashion, making it so that cells can continue to divide.
14. What is the relationship between telomerase and cancer?
A: Cancer cells are cells that divide rapidly, uncontrollably, and infinitely. It is impossible for a cell to divide forever (infinitely) without some means of keeping its telomeres from becoming too short. All cells in the body have the gene for telomerase, but it is usually only expressed in a few types of cells such as sperm and egg cells. In contrast, most cancer cells actively produce significant amounts of telomerase, making them immortal. The ability of a cell to produce telomerase can therefore represent a large step towards becoming cancerous.
15. List seven types of cancer. For each type, list one risk factor. If you do not know any, don’t list any.
A: The following is summarized from a 1996 Scientific American Article, available at http://www.sciam.com/0996issue/0996allcancers.html. More oncogenes are discovered all the time. A family history and smoking are generally considered risk factors for all cancers. Prostrate cancer: Increasing age; possibly a high-fat diet. Breast cancer: Inherited mutations in the BRCA1 or BRCA2 genes, increasing age, personal or family history of breast cancer, possibly a high-fat diet, and many others still unproven. Lung cancer: Cigarette smoking; exposure in the workplace to certain substances, including asbestos and some organic chemicals; radiation exposure; radon exposure (especially in smokers); environmental tobacco smoke. Colorectal cancer: Polyps or inflammatory bowel disease, living in an industrial or urban area, possibly physical inactivity, exposure to certain chemicals and a high-fat or low-fiber diet. Bladder cancer: smoking, working in the rubber, chemical and leather industries, or as a hairdresser, machinist, metalworker, printer, painter, textile worker or truck driver. Cervical cancer: many sexual partners (at least partly because of attendant risk of sexually transmitted papillomaviruses); cigarette smoking. Skin cancer (melanoma): sun exposure, especially during childhood; pale or light skin. Leukemia: Certain genetic abnormalities, including Down's syndrome, Bloom syndrome and ataxia-telangiectasia; excessive exposure to ionizing radiation and some chemicals, such as benzene, found in lead-free gasoline; exposure to the virus HTLV-I.
16. What are tumor suppressor genes and what do they have to do with cancer?
A: Tumor suppressor genes code for the production of proteins that prevent cell division, usually in neighboring cells. If a cell is not producing these proteins or is no longer is receptive to them, it may divide too much, possibly leading to cancer. See http://www.sciam.com/0996issue/0996weinbergdiagram1.html.
17. What are growth factors and what do they have to do with cancer?
A: Growth factors are proteins that promote cell division. Many cancerous cells either overproduce growth factors or act like the factors are there when they are not. See http://www.sciam.com/0996issue/0996weinbergdiagram1.html.
18. Provide answers to review #1, 5-14 at the end of Chapter 13 (p. 352)
5. Natural killer cells are a type of white blood cell that recognizes abnormal cells in the body (such as a virus infected cell or a tumor cell) and destroys them. Interferons are proteins that are secreted by a cell when it is infected by a virus, and that activate natural killer cells. Complement proteins enhance the immune system by degrading the cell walls of bacteria, stimulating the release of histamine, attracting phagocytes to an infected area and attaching to pathogens.
6. The process of inflammation begins with histamine being released from injured mast cells in tissue. The histamine causes vasodialation and increased plasma flow from the local capillaries, resulting in redness, warmth and swelling. Prostaglandins are also released from damaged cells, stimulating the congregation of phagocytes and the sensation of pain. As phagocytes begin to “devour” bacterial invaders, kinins are produced, which further attract phagocytes to the area. Once the invaders and damaged tissue has been cleared by phagocytes tissue repair occurs, healing the area.
7. Killer (cytotoxic) T cells secrete substances that kill abnormal cells. Helper T cells secrete interleukins (signaling proteins) that stimulate cytotoxic T cells to abnormal cells, and B cells to secrete antibodies. Suppressor T cells decrease the activity of other T cells and B cells.
8. Plasma cells are B cells with a short lifespan that produce and secrete large amounts of antibodies. This short-term response to an antigen is known as the primary response. Memory cells produce antibodies on their surface and can remain in circulation for years. If they encounter their specific antigen, they will rapidly differentiate to produce new plasma cells that secrete antibodies. This is known as the secondary immune response.
9. The genes that code for antigens are short sequences that have high rates of recombination and can be arranged in many different ways.
10. Clonal selection occurs when a lymphocyte binds to an antigen and proliferates, producing other lymphocytes with the same antigen receptors.
11. IgG Antibody
12. IgG antibodies are the most prevalent type, and are found in the blood, lymph, tissue fluid and intestines. They provide protection against various pathogens and can cross the placenta from mother to fetus. IgA antibodies are the second most prevalent type, and are found in the tears, mucus, milk, saliva, blood, lymph, and digestive fluids. They protect mucus membranes and are produced less during times of stress. IgM antibodies are found in the blood and lymph and are the first immunoglobulins to be produced following contact to an antigen, due to their ability to lyse microorganisms. IgD antibodies are found in the blood, lymph, and on the surface of B cells and are believed to be involved with the activation of B cells. IgE antibodies are found in the B cells, mast cells, basophils, and in the blood plasma during an allergic reaction. They trigger the release of histamine.
13. See number 8 above.
14. Vaccines activate B cells so that they produce memory cells, which will react quickly and efficiently if the person is ever exposed to the same antigen later in life.
19. You need to collect and GRADE study sheets turned in by students who are not getting upper division credit. You must provided useful comments on these papers or you will not receive upper division credit. See me for clarification and to obtain these papers which you will grade.