Control of Gene Expression in Bacteria Flashcards
What does constitutive mean?
Always on, essential component of all living things
What is inducible/Repressible? Why is it important?
Inducible = turned on
Repressible = turned off
Needed for cell growth under certain conditions
DNA binding proteins
common in both euk and prok, can be activators or repressors of transcription through non covalent binding, binds to promoter which recruits or prevents RNA polly from interacting
What is transcription in bacteria regulated by?
Operons - overlap with promoter and transcription start site
What are negative regulatory proteins?
When binded inhibits transcription
What are positive regualtory proteins?
When binded activates transcription
Inducible operons
off->on
Repressible operons
on->off
Negative inducible
Regulatory protein is a repressor which blocks binding of polly to promoter, so an inducer binds to inhibitor to inactive it to turn on transcription (ex. metabolism)
An inducer binds to the inhibitor thats on the promoter and inactivates it turning transcription
Negative Repressible
Regulatory protein is a repressor so it blocks binding of polly to promoter. To turn off transcription a cofactor/corepressor needs to bind to repressor to allow it to bind to promoter inhibiting transcription. (ex. biosynthesis)
So transcription is on and to turn it off a cofactor is needed to bind to the repressor so the repressor can bind to promoter inhibiting transcription.
Positive Control
regulator protein is an activator, it binds to operon and induces transcription = CAMP or CAP catabolite activator protein
CAMP or CAP catabolite activator protein
binds upstream promoter enhancing binding of RNA polly to promoter
What is the lac operon?
negative inducible - regulatory protein is an inhibitor that must be turned on
What inactivates the inhibitor in the lac operon? And what can it be metabolized by?
lactose, E.coli
How does E.coli metabolize lactose?
Lactose gets transported across cell membrane by permase (LacY), then E.coli breaks lactose down into glc and gal that is catalyzed by B-galactosidase (lacZ) which can also convert lactose to allolactose. The third enzyme lacA (thiogalactoside) function is unknown.
What is coordinate induction?
simultaneous synthesis of several proteins by an inducer
What happens when no lactose is present? What binds to what inhibiting transcription?
What is lactose broken down by?
What binds to repressor causing repressor to be removed from operator?
What binds to promoter inducing the expression of Lac Z,Y,A?
What is lactose converted into?
What happens when lactose is depleted?
- Repressor protein (LacI) binds to operator (LacO) and inhibits transcription.
- Lactose is broken down by the little bit of B-galactosidase that is made.
- Allolactose binds to repressor and causes repressor to be removed from operator.
- RNA poly binds to promoter and induces expression of Lac Z,Y,A.
- Lactose in converted to glucose and galactose (and some allolactose to keep operon in on position).
- When lactose is depleted, no more allolactose is made and the repressor binds to operator inhibiting transcription.
Regulation of expression can be in cis and trans, what is cis what is trans?
Cis - control gene expression is on the same piece of DNA
Trans - control gene expression on other DNA molecules
What happens if bacteria has a mutation on Lacz- gene but not lacY+ gene in genome and mutation in LacY- gene but not LacZ+ gene in plasmid?
They are complimentary so the wild type will show and produce lactose
What is LacI+?
What is produced and what can it bind to?
What does it repress in the absence of?
What happens when lactose is present?
Is the mutant repressor is dom or rec to wild type repressor?
- Trans dominant
- A repressor is produced and can bind to both operators
- It represses transcription in absence of lactose
- When lactose is present it inactivates the repressor and functional B-galactosidase is produced
- Therefore mutant repressor is recessive to wild type repressor.
What happens if LacI has a mutation (LacIs)
It becomes insensitive to allolactose so the mutant repressor (LacIs) binds to operator in the presence/absence of allolactose.
Therefore the mutant repressor is dominant over wild type supprrepressor
What happens when glucose is high in respect to CAMP levels?
Camp levels are reduced, reducing affinity of polymerase to promoter, reducing expression of the lac operon.
