L11: Regulation of prokaryote gene expression Flashcards
What is the primary mechanism of gene expression regulation in bacteria?
Transcriptional control
What are housekeeping genes and why are they important?
Genes required for basic cellular maintenance
2 types of transcriptional control & describe them
Positive regulation: Activator protein binds to DNA & activates transcription
Negative regulation: Repressor protein binds to DNA & prevents transcription
How does the lac operon respond to the presence of lactose?
It induces transcription by inactivating the repressor protein
What is the function of the lac repressor protein?
To prevent transcription of the lac operon
What is the significance of the CAP-cAMP complex in the regulation of the lac operon?
It enhances transcription by binding to the promoter region.
Function of promotor in the lac operon structure
Binds RNA polymerase & initiates transcription
Function of operator in the lac operon structure
Binds lac repressor protein and blocks transcription
Structural genes of the lac operon
lacZ, lacY, lacA
Function of lac operon proteins
lacZ: breaks down lactose into glucose+galactose AND produces allolactose
lacY: transport lactose into cell
lacA: Encode protein that allow bacteria to use lactose as an energy source
Function of lacL gene
Produces lac repressor protein which binds the operator & blocks transcription
Inducer compound of the lac operon
Allolactose
2 features of the lac repressor protein
1) DNA-binding domain that binds to the operator sequence (lacO)
2) Domain that binds the inducer, allolactose
What is allolactose?
Produced by breakdown of lactose by lacZ
What role does allolactose play in the regulation of the lac operon?
It binds to the repressor, preventing it from binding to the operator
Describe the absence of lactose in lac operon
Lac operon expressed at VERY LOW LEVELS
- when lactose is absent, there is no allolacose in the cell
- lac repressor protein binds to operator (lacO), preventing transcription
Describe the presence of lacose in lac operon
Transcription of lac operon is induced
1) b-galactosidase produce allolactose and this binds to lac represspr
2) Formation of allolactose-lac repressor complex alters DNA-binding domain of lac repressor & prevent it binding the operator
Describe lacl- mutation
Mutant lac repressor protein can NOT bind to opertor so lac operon constitutively expressed (always ON)
Describe lacO^c mutation
Operator sequence mutated, lac repressor protein can NOT bind, so lac operon constitutively expressed
Describe lacl^s mutation
Mutant repressor protein cannot bind to allolactose so it always binds to operator, operon always OFF
What role does allolactose play in the regulation of the lac operon?
It binds to the repressor, preventing it from binding to the operator
What is the arabinose operon and how is it regulated?
It degrades arabinose, where araC forms a DNA loop preventing transcription without arabinose
What is the impact of having no arabinose on the expression of the ara operon?
There is no expression of the ara operon
What type of mRNA is produced from the lac operon, and what does this imply about its translation?
Polycistronic mRNA, implying coordinated translation of multiple proteins
How does the presence of glucose influence the expression of the lac operon?
Glucose decreases the transcription of the lac operon
What is the significance of the polycistronic mRNA produced by the lac operon?
It allows for the simultaneous synthesis of multiple proteins
How does the araC protein regulate the arabinose operon?
it forms a DNA loop to inhibit transcription without arabinose
What is the structure of the lac operon, including its regulatory regions?
Promoter, operator, and CAP binding site
How do mutations in the lac operon provide insights into its function?
They reveal the regulatory roles of individual components through altered gene expression
What vectors is lac promotor used in?
Plasmid expression vectors
Which 3 enzymes does the arabinose operon produce?
araB, araA & araD which break down arabinose
Describe the DNA loop model when there is NO ARABINOSE
araC protein binds to aral & araO2 which form a DNA loop to stop RNA pol & CAP-cAMP
- preventing expression of the ara operon
Describe the DNA loop model when ARABINOSE IS PRESENT
Arabinose binds to araC, breaking DNA loop and RNA pol can transcribe again
- A 2nd araC-arabinose complex binds to aral & increases RNA pol affinity to promotor Para
- CAP-cAMP binds the CAP binding site & RNA pol binds to promotor to initiate transcription
