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Control of Gene Expression in Prokaryotes

by: Matt Pawlush

Control of Gene Expression in Prokaryotes BIOSCI0716

Marketplace > Biology > BIOSCI0716 > Control of Gene Expression in Prokaryotes
Matt Pawlush
GPA 101.3
Biology II
Dr. Curto

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Biology II
Dr. Curto
Class Notes
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This 3 page Class Notes was uploaded by Matt Pawlush on Friday February 20, 2015. The Class Notes belongs to BIOSCI0716 at a university taught by Dr. Curto in Fall. Since its upload, it has received 150 views.


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Date Created: 02/20/15
Control of Gene Expression in Prokaryotes Gene Expression is when a gene product is synthesized and that protein product is active in the cell Different levels of control Replication control Transcriptional control Translational control Post translational control Although DNA is present all of the time in a cell it is not accessed all of the time Some genes operate all of the time these are housekeeping genes gt They are constitutively expressed they are continuously at a low level of transcription Housekeeping genes are also used as a basis for comparison of expression of other genes in other situations Genes may be turned on or off in response to environmental conditions such as food availability Negative control transcription is blocked When it is not needed Positive control transcription is promoted When needed The Lac Operon if glucose is present there is no need to break down to lactose and the lac operon should be off 3 enzymes for lactose metabolism Beta gal Lac Z gene splits the lactose disaccharide into glucose and galactose Galactoside permease Lac Y gene lets lactose into the cell Transacetylase Lac A gene function unkown An operon is a segment of DNA containing structural genes and control areas Control areas are acted on by proteins that control Whether the gene is expressed or not A collection of genes are under the control of a single promoter A promoter is a segment of DNA Where RNA polymerase binds to start transcription The Lac operon is POLYCISTRONIC meaning that it contains more than one protein coding segment To turn on the Lac operon lactose must be present and glucose must be absent A repressor is mad by the Lac I gene It is constitutively expressed and binds to the operator Genes ZY and A are off A repressor is a DNA binding protein Lactose is an inducer it binds to a repressor and removes it from the operon Glucose inhibits lactose into the cell through galactoside permease it is an inducer excluder Negative control repressor blocks transcription glucose prevents entry of lactose The Lac operon is inducible and lactose is the inducer Ara operon positive control of gene expression used in the metabolism of arabinose Ara C is both an activator and repressor depending on the presence of arabinose In the presence of arabinose it changes conformation so RNA polymerase can bind In the absence of arabinose Ara C takes a conformation that blocks transcription Trp Operon is a repressible gene Tryptophan is an amino acid Trp operon is on unless it is shut off by ample amounts of trip trp operon is a repressible system trip is the corepressor It changes the conformation of the repressor to bind to DNA In the presence of high amounts of trp sections 3 amp 4 of the operon base pair forming a stem loop and acting as a terminator sequence Low TrpSlow translation Catabolic lac operon breaks apart When necessary induced by the presence of the target Anabolic trp operon Put together until you have enough and is then turned off


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