PROKARYOTIC EXPRESSION Flashcards
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Why is it important to regulate gene expression?
- why produce unrequired proteins?
- important for differentiation in eukaryotic development
- transcription and translation are energy consuming processes
- genes/ protein products are often required in different environments
- genes/ protein products are often required in different quantities
Majority of regulation is done at the ___ level.
transcriptional
How is gene expression regulated post transcriptionally?
- folding of mRNA can prevent translation
- protein modification
The strength of sigma 70 is based on the ____ ____, changing the probability that RNA polymerase is recruited.
binding sequence
What is positive regulation?
uses transcriptional activators, so that gene is active in the presence of transcriptional factors
- 1 part of activator binds to DNA near promoter and another recruits RNA polymerase
What is negative regulation?
gene is active in the absence of transcriptional factor
- bind to operator region and blocks access of RNA polymerase of inhibits its action
What is an operon ?
- a cluster of genes regulated by a single promoter and expressed together as a unit
Lac operon is _____ regulated by cap (___ ___ ___).
WHY?
positively
catabolite activating protein
- glucose is preferred energy source, occurs in low glucose conditions.
What does laci do as a repressor?
- produces a product that normally binds to the operator (lacO), which blocks RNA polymerase
When lactose is present what happens?
-lactose binds to laci, causing a conformational change meaning it can no bind to lacO and RNA polymerase can initiate transcription
Laci repressor acts in ___, meaning it can spread to other operons.
trans
LacO operates in __, meaning mutants are only affecting the specific operon.
cis
What activates CAP?
- causes extra enhancement
cAMP
- binds to CAP and causes an allosteric change to allow RNA polymerase recruitment, becomes a promoter at alpha sub unit of RNA polymerase
Function of Y gene in lac operon
permease
Function of Z gene
to cut galactoside into galactose and glucose
Trp operon is __(a)__ regulated by tryptophan, which binds to the _(b)__, activating it. The repressor then binds to operator to initiate __(c)__.
a) negatively
b) repressor
c) transcription
How are the lac operon and trp operons different yet are still both negatively regulated?
Trp operon good example of ___ inhibition.
- Lac operon is inactive in the absence of lactose
- Trp operon is inactive in the presence of tryptophan
- feedback
ara operon is ____ regulated
positively
what are araBAD genes required for?
metabolism of arabinose
max araBAD expression requires what?
a CAP
When arabinose is present, binds to _(a)__ to recruit __(b)__ at _(c)___ region.
a) araC
b) Rna pol
c) initiator
When arabinose is absent, araC has ___-(a)____ conformation and binds as dimer to operator (__(b)__) and inducer ((c)) regions.
a) anti- activator
b) araO
c) I1
What are regulons? Used to respond to ?
groups of operons regulated together
- environmental fluctuations
Different sigma factors are used to….
-Important sigma factor in heat shock regulation ?
direct R pol to different promoter sets
- sigma factor 32
What is a constitutive mutant?
where the lack operons are ALWAYS active causing unregulated gene expression
