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Bacterial Gene Expression: Operon Model

Terms in this set (24)

Operator (within the promoter)
On-off switch
Operon
the entire stretch of DNA that includes the operator, the promoter, and the genes that they control
Tryptophan present
Binds to the trip repressor protein and turns the Operon off
Operon off
Protein repressor
Repressor is active
Presence of a corepressor
trip operon off
If tryptophan levels are high
Repressor prevents gene transcription by
binding to the operator and blocking RNA polymerase
Repressor is the product
a separate regulatory gene
Repressive operon
On but turns off when repressor to the operator shuts of transcription
Repressive operon??
Trp
Inductible operon
Off but inducer inactivated the repressor and turns on transcription
Inductible operon??
Lac operon
Lac repressor active
Switches lac operon off and inducer activates the repressor to turn the lac operon on.
Inductible enzymes pathway?
Catabolic pathways and chemical signals
Repressible enzymes pathway?
Anabolic pathways and high levels of the end product.
Regulation of trp and lac operons
Negative control and operons are switched off by the active form of the repressor.
Some operons are subject to...
Positive control through a stimulatory protein (CAP)- an activator of transcription.
Glucose is scarce...
CAP is activated by binding with Cyclic AMP.
Activated CAP
Attaches to promoter of lac operon, increasing the affinity of RNA Polymerase.
Glucose levels increase-
CAP detaches from the lac operon and transcription is at a normal rate.
Tryptophan absent,
repressor inactive, operon on
Tryptophan present,
repressor active, operon off
lactose absent
repressor active, operon off
lactose present
repressor inactive, operon on
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