BCEM 393 Lecture Notes - Lecture 16: Skeletal Muscle, Tamoxifen, Anabolic Steroid
27 Jun 2018
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Eukaryotic Transcription
REVIEW OF PROKARYOTIC TRANSCRIPTION REGULATION OF LAC OPERON
-Repressor prevents gene expression by binding to operator (“controlling”) region
-Lac operon is an inducible set of genes which are responsible for the breakdown of lactose
into sugars used for cellular metabolism
-Gene expression can be induced upon the arrival of an inducer molecule in the cell
-Repressors prevent gene expression by binding to the upstream controlling region (the oper-
ator)
-Lactose is the lac operon inducer molecule
-Lactose binds to the repressor. This binding releases the repressor from the operator, thereby
allowing gene expression
-After the release of the repressor, RNA polymerase begins transcription of the operon
-2 proteins:
-Beta-galactosidase: breaks down lactose into two simple sugars (glucose and galactose)
-When concentration of beta-galactosidase is reduced, lactose unbinds from the repres-
sor, which rebinds to the operator, and transcription halts
-Permease: membrane bound protein, which provides a direct route for lactose outside the
cell to enter. This import happens at a much greater rate than passive transfer because
translation continues inside the cell
-Other permease proteins become embedded in the cell membrane, which further increases
the rate at which lactose enters the cell
LAC REPRESSOR AND LAC OPERON
-Lac operon is a set of genes which code for and regulate the expression of genes involved in
the utilization of lactose in E. coli
-i-genes code for the lac repressor
-p is the promoter
-Binding the lac-repressor to the operator region interferes with the binding of RNA poly-
merase and thus decreases transcription of the z, y, and a-genes
-z-gene codes for beta-galactosidase
-Lactose gets changed into allolactose which is the “inducer”
-When the inducer binds to the repressor, the repressor cannot bind to the operator region,
thereby allowing RNA polymerase to bind and start transcription
-When the repressor doesn't bind to the DNA, then RNA polymerase transcribes the genes
and beta-galactosidase is formed
CAP = CATABOLITE ACTIVATOR PROTEIN
-When glucose concentrations decrease, cAMP concentrations increase, and there is an ex-
pression of the lac operon genes
-CAP binds to cAMP
-CAP * cAMP binds to DNA of Lac Operon at -61
-CAP * cAMP * DNA stimulates RNA polymerase
-CAP = cAMP Response Protein = CRP
DIFFERENTIATION OF CELLS
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Document Summary
Review of prokaryotic transcription regulation of lac operon. Repressor prevents gene expression by binding to operator ( controlling ) region. Lac operon is an inducible set of genes which are responsible for the breakdown of lactose into sugars used for cellular metabolism. Gene expression can be induced upon the arrival of an inducer molecule in the cell. Repressors prevent gene expression by binding to the upstream controlling region (the oper- ator) Lactose is the lac operon inducer molecule. This binding releases the repressor from the operator, thereby allowing gene expression. After the release of the repressor, rna polymerase begins transcription of the operon. Beta-galactosidase: breaks down lactose into two simple sugars (glucose and galactose) When concentration of beta-galactosidase is reduced, lactose unbinds from the repres- sor, which rebinds to the operator, and transcription halts. Permease: membrane bound protein, which provides a direct route for lactose outside the cell to enter.
