1362-SU09-Lecture-5-_40772

1362-SU09-Lecture-5-_40772 - RegulationofGeneExpression

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Regulation of Gene Expression Cells control the quantity and types of proteins being formed: ell’s 000’s of 1000’s of …having a multitude of functions: Cell s chromo some(s) 1000’s of Genes gene expression Proteins… Enzymes Transport proteins Receptor proteins ELP TO CONTROL Does an organism need all of its’ genes expressed 24/7? Structural proteins egulatory proteins Development HELP TO CONTROL GENE EXPRESSION p / Regulatory proteins – Extracellular, environmental changes influence gene expression –G en e regulatory processes are efficient; cells are not wasteful e expression is often regulated at the transcriptional stage, however genes can be controlled at multiple levels within the cell.
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Tryptophan (trp) is an amino acid essential for survival. The Example of Prokaryotic Gene Regulation regulation of tryptophan synthesis in bacteria is dictated by the absence or presence of tryptophan in its surrounding environment: Trp absent: synthesize it Tryptophan Trp present: use available tryptophan and shut down internal trp synthesis itself can block transcription of genes ding for Two levels of regulation are operable: ost anslational alter nzyme coding for enzymes Post translational : alter en yme activity via feedback inhibition Transcriptional: alter expression of genes encoding enzymes Tryptophan can activate nzyme End result: tight control of trypto han synthesis inactivate enzyme 1 of pathway. phan synthesis according to the cell’s needs.
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Prokaryotic Gene Organization Bacterial genes that function in the same metabolic pathway are grouped together in an operon . Operon = Promoter + Operator + Structural genes Structural genes: transcribed into proteins that execute the metabolic Structural pathway. Promoter: RNA polymerase binding site Operator: transcriptional control element Promoter genes Regulatory ene Operator Do not code for proteins A B C gene p Repressor protein Binds to operator blocking anscription. roteins (enzymes) of Regulatory gene : upstream from operon; its’ regulatory protein ) tl ti t i i th t transcription. Proteins (enzymes) of pathway (repressor) controls transcription via the operator. Activity of the repressor depends on the control mechanism ** • Active repressor: binds operator; Inactive repressor: does not bind operator
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Mechanisms of Repressor Control I •P r o k a r y o t i c operons can be categorized as inducible, repressible, or constitutive •T h e structural genes of repressible operons usually code for enzyme proteins involved in the synthesis (anabolism) of substrates critical for epressible perons: are expressed ntil other olecule co growth & sustenance. – Example: tryptophan operon Repressible operons: are expressed until another molecule, a co repressor, binds to the repressor activating it.
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This note was uploaded on 03/09/2010 for the course BIO 1362 taught by Professor Knapp during the Spring '10 term at University of Houston-Victoria.

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1362-SU09-Lecture-5-_40772 - RegulationofGeneExpression

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