ProkaryGeneRegulation211S - Virus and Prokaryotic Gene...

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Virus and Prokaryotic Gene Regulation - 1 We have discussed the molecular structure of DNA and its function in DNA duplication and in transcription and protein synthesis. We now turn to how cells regulate gene expression. Gene regulation is one of the most active areas of genetic research. Some of the answers to how genes are regulated are coming from work on recombinant DNA research, some from genetics, including the effect of mutations on gene expression, and some from research on disease. Much is coming from our increasing knowledge of cancers and the failure of the body to control cell division in cancer formation. It is important for cells to be able to control gene activity. We have genetic information for thousands of proteins. We do not want to synthesize enzymes that are not needed, nor do we want to synthesize molecules in greater quantity than needed. Our discussion on gene regulation will include looking how gene expression is regulated in viruses, in prokaryotes and in eukaryotes from regulating access to DNA to affecting the post translation processing of proteins. Viruses are mobile genetic elements or infectious genetic elements that regulate gene expression by using the DNA replication, transcription and translation processes of their host cells to synthesis new virus genetic material and coatings. Prokaryotes, in general, control genes for rapid response to their environment. By selectively activating (inducing) or inhibiting gene activity, bacterial cells can take advantage of changing conditions. For eukaryotes, gene regulation is tied to maintaining homeostasis – a consistent internal environment in the face of ever-changing external conditions. Multicellular organisms require different genes at different times of growth and development in different tissues. We have more complex controls of gene expression to ensure that genes function selectively and appropriately in our different tissues from the zygote through all stages of growth, development and maturation. Gene control is exerted chemically in two general ways: affecting molecules that interact with DNA, RNA and/or the polypeptide chains, or controlling the synthesis of an enzyme or the activity of an enzyme in the cell.
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Virus and Prokaryotic Gene Regulation - 2 Gene controls can be positive – inducing or activating gene activity, or negative repressing gene activity. Recall that initiation of transcription involves a set of transcription factors that locate the promoter region of the gene to be transcribed and position RNA polymerase on the DNA for transcription. Once fixed into position, RNA polymerase catalyzes transcription. In negative control, the gene is normally transcribed, with the promoter region readily accessible to transcription factors. To stop transcription, a repressor molecule must bind to the DNA at a repressor site blocking transcription.
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ProkaryGeneRegulation211S - Virus and Prokaryotic Gene...

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