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MCDB XL 100 Chapter 20 Questions and answers | Updated
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MCDB XL 100 Chapter 20 Questions and answers | Updated
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MCDB XL 100 Chapter 20 Questions andanswers | Updated
Chondroma
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A benign neoplasia of cartilage is called a:
Chondrosarcoma
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A malignant neoplasia of cartilage is called a: ii ii ii ii ii ii ii ii ii ii ii ii ii ii ii
Among the following cancers, one is currently leading to the most number of deaths in the
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United States and in the rest of the world. In the United States, it contributes to cancer
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mortality more than the next three killing cancers combined. Worldwide, it claims more
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than 1.5 million lives every year. Which cancer is this?
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A. Lung cancer
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B. Breast cancer
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C. Colon cancerii ii
D. Pancreatic cancer
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E. Stomach cancer
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In medical oncology, PET (positron emission tomography) is used to selectively image
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tumors in the body and to monitor cancer progression and response to treatment. Before ii ii ii ii ii ii ii ii ii ii ii ii ii ii ii
performing a PET scan, the patient should fast for at least several hours for blood glucose
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to be sufficiently low. At the time of the scan, the positron-emitting glucose analog ii ii ii ii ii ii ii ii ii ii ii ii ii
fluorodeoxyglucose (FDG) is injected into the bloodstream and the patient is asked to wait
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for up to an hour while avoiding physical activity. Finally, the scanner moves slowly over
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the body to reveal the location of possible tumors. Why do you think the patient should
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avoid physical activity before the scan?
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To prevent the absorption of the radioactive tracer by healthy tissues.
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When the blood glucose level is low, the added radioactive glucose analog is preferentially
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and rapidly taken up by tumor cells as a result of the Warburg effect. Physical activity
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stimulates uptake by muscle cells also (including heart muscle), which interferes with the
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imaging. ii ii ii ii ii ii ii ii ii ii ii
Mutations in two important cancer-critical genes, encoding p53 and Rb, respectively, are ii ii ii ii ii ii ii ii ii ii ii ii
commonly found in cancers. What type of mutations are these expected to be? ii ii ii ii
Loss-of-function mutations in both genes
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Both p53 and Rb are coded by tumor suppressor genes, and their inactivation promotes
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cancer. ii ii ii ii ii ii ii ii ii ii ii ii ii
The homologous chromosome pairs in our cells do not carry identical sequences in all
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loci. This heterozygosity (difference between the two copies) can be altered in cancer: in
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fact, ii ii ii ii ii ii ii ii ii ii ii ii ii ii
loss of heterozygosity at many loci is observed in cancer cells, through an increase in
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either ii ii ii ii ii ii ii ii ii ii ii
homozygosity (two identical copies) or hemizygosity (i.e. loss of one copy). Researchers
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can take advantage of this loss of heterozygosity in cancer cells to identify genomic loci
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that contain cancer-critical genes. What type of gene would you expect to find in
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chromosomal regions with a loss of heterozygosity? Proto-oncogenes (P) or tumor
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suppressor genes (T)?
T
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Once the first copy of a tumor suppressor gene is lost or inactivated, the remaining copy is
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commonly lost by a less specific mechanism, leading to loss of heterozygosity in the gene
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as well as in its neighboring loci. This represents a way of finding loci that contain tumor
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suppressor genes. ii ii ii ii ii ii ii ii ii ii
The immortalized non-malignant mouse cell line NIH-3T3 was derived from normal
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mouse fibroblasts in the early 1960s. These cells are able to readily take up exogenous
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DNA and are prone to transformation by cancer-causing agents, including some
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retroviruses. DNA extracted from a human bladder carcinoma line is able to transform
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these cells, as judged by a significant increase in the number of foci (cell clumps) in the
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cell-culture plates when the DNA is added. The malignant cells contain human DNA, and
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the DNA can be shown by sequence analysis to contain a single mutant gene that is
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present in the original bladder carcinoma cell line. The gene codes for a monomeric G
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protein and was one of the first cancer-critical genes to
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be identified in this way. The protein encoded by this gene is:
Ras
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Ras was also found earlier to be the oncogene carried by some sarcoma viruses, and the
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identification of the same gene (with similar mutations) in both cases was an important
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discovery that advanced our understanding of the molecular biology of cancer. ii ii ii ii ii ii ii ii ii ii ii ii ii
Retinoblastoma is an early-onset cancer of the retina with a rapid progression, and is
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mostly diagnosed in children. In its hereditary form, multiple eye tumors usually arise in
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both ii ii ii ii ii ii ii ii ii ii ii ii
eyes, while the nonhereditary form usually causes fewer tumors in only one eye.
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Treatment may ii ii ii ii ii ii ii ii ii ii ii
involve a combination of chemotherapy, radiotherapy, and other therapies and the majority
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of patients can be cured if given the right treatment. However, survivors of one form of ii ii ii ii ii ii ii ii ii ii ii
retinoblastoma (and not the other form) have a markedly increased frequency of
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subsequent neoplasms that can lead to other cancers later in life, especially soft-tissue
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sarcomas. These patients should therefore be closely monitored throughout their lives.
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Which gene is affected by the primary driver mutation in this cancer as well as the later
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sarcomas? Which form of retinoblastoma do you think is associated with a higher risk of
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subsequent neoplasms?
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Rb; hereditary
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a; 1
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Most cancers arise from dominant somatic mutations in cancer genes; however, most
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germ-line mutations are recessive, which enables them to be carried through generations.
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You have analyzed a large set of human cancer-critical genes for a selected group of
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carcinomas, ii ii ii ii ii ii ii ii ii ii ii ii ii ii
classifying each of the genes based on whether they are known to undergo somatic or
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germ-line mutations, as well as based on whether they are dominant or recessive. You
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