11-18-09_GeneExpression_OmicsD

11-18-09_GeneExpression_OmicsD - Omics and Bioinformatics...

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Omics and Bioinformatics Number 6 : Where am I? Number 2 : In the Village. Number 6 : What do you want? Number 2 : We want information. Number 6 : Whose side are you on? Number 2 : That would be telling. We want information. .. information. .. information. Number 6 : You won't get it. Number 2 : By hook or by crook, we will. Number 6 : Who are you? Number 2 : The new Number 2. Number 6 : Who is Number 1? Number 2 : You are Number 6. Number 6 : I am not a number, I am a free man. From “The Prisoner” (also the intro to an Iron Maiden song)
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“Silent” mutations in codons – from June 2009 Scientific American magazine A silent mutation is one where changing the codon does not change the amino acid coded . Biased usage of codons was observed and a potential function soon became apparent: certain codons enhanced the rate or accuracy of protein synthesis. a gene that contains more of the codons matching the relatively abundant tRNAs would be translated faster, because the higher concentration of those tRNAs would make them more likely to be present when needed. For example, although the codons GGA and GGG, which encode glycine, can both occur in splicing enhancers, the former codon acts as a more potent enhancer, leading to more efficient splicing. GGA is also correspondingly more common close to the ends of exons.
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Three levels of control of gene expression Transcriptional-level control: whether and how often a gene can be transcribed Processing-level control: how a pre-mRNA is processed into a mature mRNA (e.g. alternative splicing) Translational-level control: whether and how often mRNA can be translated, also mRNA stability
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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
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This note was uploaded on 02/09/2010 for the course BIOL 230 taught by Professor Bartlett,e during the Fall '08 term at Purdue University.

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11-18-09_GeneExpression_OmicsD - Omics and Bioinformatics...

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