Lecture 15 Flashcards
What is enzyme induction?
- Bacteria only produce enzymes required for growth on particular substrate in the presence of the molecule
- It’s an efficient system as bacteria are exposed to different nutrients/conditions
-Enzyme induction is a process in which a molecule induces the expression of an enzyme.
What is a promotor?
Binds RNA Pol and initiates transcription -> mRNA
What is an operator?
Binds regulatory proteins to alter transcription
What is negative regulation mediated by?
A repressor
What is the role of a repressor?
A regulatory protein that turns off gene expression
How does the repressor act?
The repressor binds to the operator and can block the polymerase from moving past the repressor/accessing the promotor region
What is positive regulation mediated by?
An activator
What is the role of an activator?
A regulatory protein that turns on gene expression
How does the activator act?
The activator binds to the operator and assists with binding of RNA pol
What is the effect of a weak promotor in the absence of the activator?
They won’t transcribe as well
An inactive activator = ?
No expression
An inactive repressor = ?
Constitutive expression (genes keep expressing)
What is the repressors relation to the lac operon?
It controls the lac operon
What is the effect of an inducer?
A repressor would normally bind to the operator and turn off expression but if the inducer is present, this will block the repressor effect
The lac operon is only transcribed in the presence of …
Lactose
-No lactose = repressor stops expression of Lac
How does Lactose work in the Lac gene?
It is able to bind to LacI promotor as an effector, this alters its binding abilities meaning it’s unable to bind to DNA -> enabling DNA pol to express genes
What is a polycistronic?
mRNA producing multiple genes
(1. Inducers regulate new B-gal synthesis)
What is the effect of removing the inducer?
Synthesis of B-gal is stopped
(2. Inducers differ from substrates)
What can other molecules that are not substrates act as?
Inducers
- The component that recognises the inducer is distinct from the enzyme
- > one recognises the inducer, one breaks down the substrate
(3. Genes controlled together)
What did gene mapping show about the LacZ/Y/A genes?
That they are closely linked and co-regulated
(4. LacI is a repressor)
What did they find about lacI-?
- That they were constitutive (always on) for production of enzymes
- They didn’t respond to inducer therefore were a regulatory mutant
- Mapped closely to lacZYA
What did the PajoMo experiment show?
- That LacI was a repressor
- That the L+ allele was dominant
An Fprime plasmid with a Lac+ could switch off expression in both copies of DNA. Why is this?
The protein is diffusible (trans)
-The lacI gene encodes a diffusible factor
Are operator sites diffusible?
No, they only control the downstream gene
What is O^C?
Operator Constitutive Mutants
What mutations are dominant over repressor mutations and why?
Operator mutations are dominant over repressor mutations as they are downstream in the pathway
->repressor needs to bind (to DNA) to have its effect, by taking this site there’s no site to bind
Finish the sentence
Operators are…
Cis acting
What does the repressor interact with?
The operator
What type of dominance does O^C have and to what?
O^c is cis-dominant over lacI+ and lacl^s
