12-3-08_GeneExpression_OmicsC

12-3-08_GeneExpression_OmicsC - New from Madonna! Personal...

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New from Madonna! Personal Genome Kits Tired of borderline microarray results? Here’s your lucky star!
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Announcements Written Assignment 2 due Friday, December 5, at noon. Evaluations of Prof. Bartlett are available online. TA evaluations will be made available Friday or Monday.
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Inducible operons An inducer (e.g. lactose) inactivates the repressor protein Repressor then no longer binds to operator Promoter can be bound by RNA polymerase The inducer turns on a set of appropriate genes, such as those involved in lactose breakdown When the [inducer] falls, more active repressor than inactive, and the repressor binds to the operator site. The gene for beta-galactosidase is often used as a reporter gene experimentally. Its activity will make a blue product when acting on X-Gal. Can be coupled with many promoters.
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Repressible operons In this example, if there is tryptophan in the medium, no need for cell to synthesize it Tryptophan (trp) acts as a corepressor , or a necessary cofactor for repression When tryptophan is present, it binds to the repressor and makes it active. (opposite of an inducible operon). When [trypophan] falls, need to synthesize it Not enough trp, so almost all repressors inactive That allows synthesis of tryptophan to proceed
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Regulation of the lac operon: full of CRP Scientists found that in the presence of glucose, lactose breakdown was inhibited, even if [lactose] high As [glucose] increases, cAMP decreases But, cAMP is need to bind to the cAMP receptor protein (CRP) cAMP-CRP binds in promoter region and is necessary for lac operon Presence of bound cAMP-CRP complex is necessary even when positive control because cAMP-CRP is a necessary activator for transcription Negative control occurs for the lac operon and for tryptophan synthesis because transcription is blocked when a repressor is active
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Sequence specific transcription factors can increase or decrease transcription Transcription factors are proteins that bind to various regulatory sites of particular genes (e.g. CREB); General factors or sequence specific. Transcriptional activators stimulate and transcriptional repressors inhibit transcription of adjacent genes A single gene may be controlled by many different DNA regulatory sites that bind variety of different TFs A single transcription factor may become attached to numerous sites around genome, controlling the expression of a host of different genes Each cell type has characteristic pattern of gene transcription, which is determined by the particular complement of TFs contained in that cell
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Transcription factors have a few common structural motifs to recognize specific DNA sequences Factors usually have ≥ 2 domains. A DNA- binding domain recognizes & binds to specific DNA base pair sequence An activation domain regulates transcription by interacting with other proteins
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12-3-08_GeneExpression_OmicsC - New from Madonna! Personal...

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