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Lecture 11

LECTURE 11: Cancer.doc

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University of Toronto Scarborough
Biological Sciences
Ian Brown

BIOC19 Lecture 11 Slide 3: • Brain cells are normally non-diving but they can transform into cancerous ells, causing brain tumor • Leukemia - cancer of blood cells Slide 4: • A tumor can be malignant (in which the cells of the tumor are rapidly dividing) or benign (where the cells of the tumor have gone silent or dormant) • Example of invasive: breast cancer cells can metastasize lymph lobes Slide 7: • This slide talks about carcinogens in the environment, specifically asbestos • Asbestos was used in construction/building industry in walls and ceilings because it was considered to be inert and it doesn't catch on fire (so it can be used as a fire retardant) , and it's a good insulation material • Asbestos fibers are 1200x less thick than human hair • Diagram on the right: • In the upper left, you can see that asbestos fibers enter the body through nose and mouth. They lodge as they go down in the throat/esophagus • Swallowing of the fibers can result in the development of 2 cancers: cancer in the esophagus or cancer in the larynx • It's even more problematic when the fibers enter the lung through breathing. They go to these little structures in the lung where blood vessel systems are exchanging gases (releasing CO2 and taking in O2) and asbestos fibers get lodged here and trigger lung specific asbestos induced cancer • Also, the fibers can go down into the stomach and we can get cancers of stomach and intestine Slide 8: • This slide talks about carcinogens in our diet • Western societies have higher incidence of colon cancer because our diet involves processed food, trans fats, and lots of meat products. This food passes through our intestine that's why it specifically causes cancer of the colon Slide 10: • This slide talks about carcinogens associated with personal habits • Polycyclic hydrocarbons cause mutation by inserting themselves in between DNA base pairs. Slide 11: • Radiation can also transform normal cells into cancerous • UVB and UVC rays causes skin cancer • Unfortunately, ozone layer is thinning which is allowing some UVB and UVC rays to pass through • But x rays are also very useful in medicine and that's why they are used a lot. But they are used at controlled frequency and levels. For example, in labs they put a lead blanket on the rest of the body, so that the rays only hit the target of interest Slide 12: • Early work used carcinogens and radiation as experimental inducers of cancer in lab settings to study transformation. But these agents damage cells in other ways in addition to transforming them into cancerous cells, so it's hard to tell the difference between cancer-causing effects and non-cancer causing damage. • Also, they have poor transformation efficiency. If you don't transform a 100% of the cell population, then it's hard to tell the difference between the initial transformed cells and other damaged cells. • And it's problematic to use animal models (induce cancer in a certain organ of an animal) to study transformation because although a tumor forms, you can't determine the cell type origins sometimes. Slide 13: • Viruses are more efficient inducers of cancer in lab settings • There are 2 classes of tumor viruses, depending on what nucleic acid they have in the viral head Slide 14: • Experiment with RNA tumor virus • Tumor viruses transform 100% of the cell population in tissue cultures • Isolate a bit of the lung cancer tissue, homogenize it (grind up all the cells), and you end up with cell-free lung cancer extract Slide 15: • HPV is an inducer of benign tumor in humans • Polyoma is a DNA virus with a small genome of 5000 nucleotides that encode a relatively small number of proteins. It is widely use as an inducer of cancer in tissue culture systems because it can cause a 100% transformation of tissue culture cells. Also, the investigation to see what elements of the virus trigger the cancer transformation is simplified because of its small genome so we have a better chance of determining what
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