Notes for Prokaryotic Gene Expression
Notes for Prokaryotic Gene Expression Bsci105
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This 0 page Class Notes was uploaded by Trang Le on Friday November 20, 2015. The Class Notes belongs to Bsci105 at University of Maryland taught by Dr. Alewall in Summer 2015. Since its upload, it has received 31 views. For similar materials see Intro to biological sciences in Biological Sciences at University of Maryland.
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Date Created: 11/20/15
REGULATION OF PROKARYOTIC GENE EXPRESSION Why we learn regulation of gene expression gt Altemations in gene expression occurs in all organisms It is very important because it helps the organism to evolve and adapt to changes in environment It is also important to the development and aging of multicellular organisms For humans it plays a key role in treating cancer Regulation of metabolic pathway occurs on two levels 1 inhibit the activity of first enzyme in pathway feedback inhibition rapid process and 2 repress expression of the genes encoding all subunits of the enzymes in the pathway this is a longterm response In prokaryotes regulation can occur in both anabolic and catabolic pathways The regulation of an anabolic pathway is represented through trp tryptophan biosynthesis Transcription start at the switch a segment of DNA called the operator It is positioned in the promoter or in some cases between the promoter and the enzymecoding genes The entire stretch of DNA including the operator makes up an operon a set of genes of a pathway whose transcription is controlled by a single promoter RNA polymerase can bind to promoter and transcribe the operon It can be switch off by a protein called the trp repressor that blocks the attachment site Binding of the repressor to the operator prevents binding of RNA polymerase inhibiting transcription The transcription can also be stopped with assistance of corepressor a small molecule that cooperates with repressor protein to switch off operon tryptophan is an example The trp repressor is the protein product of a regulatorv gene called trpR locates in some distance from the trp operon and has its own promoter On the other hand regulation of a catabolic pathway is represented through an inducible operon called the lac operon lac for lactose milk sugar The regulatory gene lacI located outside the operon codes for allosteric repressor protein that can switch off the lac operon by binding to the operator The lac repressor is active by itself and switch off operon In this case a specific molecule called the inducer inactivates the repressor In presence of both glucose and lactose bacterium E coli prefers glucose When sensing glucose concentration a regulatory protein called activators give positive control of operons When glucose is absent the catabolic activator protein CAP stimulates transcription from the lac operon When glucose is low an allosteric regulatory protein called cyclic AMP or cAMP accumulates bind to and activate CAP so that it can bind to the lac promoter provided lactose is also present
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