Essays_for_BIo_Test_3

Essays_for_BIo_Test_3 - 14 Oncogenes and tumor suppressor...

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14) Oncogenes and tumor suppressor genes play central roles in the transformation of normal cells to cancer cells. Review how members of these two different classes of genes contribute to cancer. How do they relate to the following: induction of cancer by radiation; induction of cancer by viruses; induction of cancer by environmental chemicals; heritability of cancer. Consider the possibility of a unified theory of cancer: cells dividing without control that relates to second messenger cascades. How can the cascade go wrong? 1. mutations in the genes that specify one of the proteins in the cascade that controls cell division in a particular cell type expression of a protein with a slightly different shape and thus activity. 2. mutations in the region of a gene (promotor region) that controls how much mRNA is produced from that gene resulting the the overproduction of the protein that that gene specifies. 3. introduction into the cell of a (human-like) gene by a virus that has one of the qualities listed above. Bishop and Varmus (Nobel Prize, 1989) discovered in a virus that caused cancer in some animal cell a gene that was nearly identical gene in the normal uninfected cells. Importantly, they found that if they transferred just this gene into a normal cell, it would become cancerous. They discovered oncogenes , single genes that cause cells to divide without restraint. Guess What??? The normal gene that this cancer gene resembled was a gene specifying a protein in the second messenger cascade, in the case of this particular virus, a protein kinase . What would you call the gene in the normal cell that the viral gene resembled? A proto- ocogene (figure 19.11) . . These different oncogenes each specify a different protein. Many of these proteins are different types of protein kinases and others are proteins that constitute one part of a second messenger cascade from signal protein, to receptor, to G protein……up to transcription factors. Question : Do all oncogenes have normal cellular homologues, that is proto-oncogenes? The answer appears to be yes? The rationale is as follows: 1) Cellular reproduction is controlled by complex processes which may differ from cell type to cell type, but which involve an elaborate series of events, each mediated by a proteins and second messenger systems. That is, growth factors (proteins) are released by a cell to act on itself and on neighbors. Growth factors are recognized by cell surface receptors , signal is transduced via a G-protein , which activates an enzyme which synthesizes a second messenger in the cytoplasm, which stimulates a specific protein kinase , which phosphorylates a cascade of specific target proteins in the cell. Some of these proteins participate in or direct cell division which control cell division. Alternatively the second messenger or phosphorylation act on transcription regulatory factors (proteins , Fig. 11.14; 19.12 ), which bind to DNA and control transcription (DNA--> RNA) at the level of the promotor region of DNA.
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