Chapter 16- Gene Regulation in Prokaryotes
Trans Acting
Able to control the expression of genes on other DNA molecules
Cis Acting
Able to control the expression of genes only when on the same piece of DNA
Permease
Actively transports lactose into the cell
Attenuation
Affects the continuation of transcription, not its initiation This action terminates the translation before it reaches the structural genes (Product for attenuation is always an amino acid)
CAP
Binds in front of the promoter which recruits polymerase and in turn boosts the transcription of the region, turns on lac and other operons
Promoter Mutations
Cis Acting, Interferes with the binding of RNA polymerase to the promoter Do not produce lac proteins with or without the presence of lactose
Constitutive Expression
Continuously expressed under normal cellular conditions
Regulator Gene
DNA sequence encoding products that affect the operon function, but aren't part of the operon
Hungry Cell?
Depends on glucose levels
Lac Z
Encodes B- Galactosidase
Lac Y
Encodes Permerase
Lac X
Encodes Transacetylase
Negative Control
Inhibit gene expression
Structural Genes
Lac Z Lac Y Lac X
Glucose is Low
Levels of cAMP are high, binds to CAP, and this complex binds to DNA Increases the efficiency of polymerase binding on the lac operon Results in high rates of transcription and translation of structural genes, producing glucose
Glucose is High
Levels of cAMP are low, and cAMP is less likely to bind to CAP RNA polymerase does not bind to DNA as effectively
Regulator Gene Mutations
Mutations of the LacI gene affect both the production of B-Galactosidase and permerase because genes for both proteins are on the same operon and are regulated coordinately.
SuperRepressors
Produced a repressor with an altered inducer-binding site, which prevented the inducer from binding to the repressor, translation was always prevented. Shuts down pathway with or without lactose Dominant
Lac P
Promoter
Operon
Promoter and additional sequences that control transcription (operator) and structure of genes
High Tryptophan Levels
Region 1 binds to region 2, which leads to the binding of region 3 and region 4, terminating transcription prematurely.
Low Tryptophan Levels
Region 2 binds to region 3, which prevents the binding of region 3 and region 4, and transcription continues.
Lac I
Regulator Gene which creates a repressor Active regulator protein (repressor), binds to the operator Allosteric regulation
Operator Mutations
Repressor protein was no longer able to bind Dominant Cis Acting
When Lactose is Present
Repressor will not bind to the operator- let transcription and translation occur Lactose is converted in to Allolactose which binds to the repressor and via allosteric regulation prevents it from binding to the operator
Positive Control
Stimulate gene expression
Structural Gene Mutations
Structure of the proteins was affected. Mapped to Lac Z and Y. These we're independent and usually only affected the product of the gene in which they occurred.
Partial Diploid
Two different DNA molecules: the full bacterial chromosome and an extra piece of DNA
Regulation
mRNA processing Stability Translation Postmodification (active protein) Primarily regulated by being transcribed or not being transcribed.