T3 module 2: prokaryotic transcriptional regulation Flashcards
Ques that regulate metabolic gene expression in E.Coli and key proteins regulated
1) changes in glucose levels
2) presence of lactose
- β-galactosidase (enzyme that breaks down lactose into glucose + galactose)
- lactose permease (transport pr that brings lactose into the cell)
operon model
Jacob + Manod
groups of functionally related genes organized into clusters that are regulated transcriptionally
operon
- promoter
- operator: “on/off” switch that controls transcription
- cluster of related genes
operon model
Jacob + Manod
operon
- promoter
- operator: “on/off” switch that controls transcription
- cluster of related genes
what is polysystronic mRNA
mRNA produced in prokaryotes that can code for multiple different proteins
lac-operon function and structure
fucntion:
structure (in order)
- lacI coding sequence (codes repressor pr-)
- promoter
- operator: lacO (binding site for repressor pr made by lacI sequence)
- lacZ (β-galactosidase)
- lacY (lactose permease)
negative transcriptional regulation of lac-operon
repressor pr- (coded by lacI sequence) binds to operator, stopping RNA polymerase from binding to promoter, stops gene expression
how?
- repressor pr- made of 4 subunits
- when all 4 bind, DNA twisted into a loop
- promoter is in loop, preventing RNAP binding
regulation
- glucose presence signals expression of repressor pr
- lactose presence changes confirmation of repressor pr so that it can’t bind to operator
positive transcriptional regulation of lac-operon
idea: glucose levels control cAMP levels which regulate transcription activator binding pr
adenylyl cyclase produces cAMP
low glucose
- active adenylyl cyclase
- high cAMP
- cAMP + CRP (transcription activator) = CRP-cAMP complex
- binds to DNA and allows transcription
- lactose also inhibits repressor protein
high glucose
- inactive adenylyl cyclase
- low cAMP
- cAMP doesn’t bind to CRP
- CRP can’t bind to DNA, so transcription does not occur *even if lactose is present
