Control of Gene Expression Flashcards
list example operons
Lac
Arp
Trp
operator
allows RNA Pol to access DNA strand and start replication
repressors
regulatory proteins that bind to operator
operon senses glucose levels, sugar/carbon source
lac operon
gene expression cleaves lac operon to
allolactose (inducer)
interacts with the repressor
when inducer is bound to repressor what happens at operator?
it is not bound to operator
you need Cap to promote transcription
CAP
catabolite repression/global regulation
requirements for transcription on lac operon
CAP active and allolactose bound to operator
what happens when: lactose but no glucose
Allolactose is inactive, not bound
CAP is bound to CAP site
transcription occurs
what happens when neither lactose or glucose is available
transcription is blocked by repressor
what happens when lactose and glucose are available
transcription is inhabited by lack of CAP
what happens when lactose is not available but glucose is
Allalactose is bound
CAP is not bound
transcription is inhibited by lac of CAP and presence of repressor
CAP requires ___ to bind
no glucose
Allalactose requires ___ to bind
no lactose
will not be bound if lactose is present
CAP activity is modulated by
cAMP
levels of cAMP are controlled by adenyl cyclase (converts ATP to cAMP) – must have high levels of adenyl cyclase to get lots of cAMP so you must have low glucose
adenyl cyclase active only when little or no glucose is present
large quantities/high levels of tryptophan acts as ___
co-repressor of Trp Operon
Trp operon is on when
tryptophan is low
activity of tryptophan as a corepressor of Trp Operon
binds to repressor protein and blocks transcription (binds operator and blocks RNA Pol)
Trp expression is regulated by:
repression (on and can be turned off) and attenuation
attenuation
alteration of translation to alternate transcription
formation of termination loop that causes dissociation of Pol thru putting pressure on
regulatory protein or Arb protein
AraC
also regulated by global regulation
AraC
regulator that does both
activates transcription and turns off transcription
3 binding sites
absence of Arb
results in bending of DNA and 2 AraC form a dimer
Arb is available
Arb binds
AraC releases
results in dimer of AraC bound to Arb at key site to promote transcription
Riboswitches
way to regulate gene expression
many systems
results in folding of leader sequence to determine if transcription continues or is terminated
depends on RNA and ability to form 2’ structure
Gram - and riboswitch
can either free up shine delgarno so that 16s can bind or not (influences what happens)
Riboswitches regulate translation of ___ in gram -
mRNA
mechanisms of Riboswitches
binding to metabolite which alters structure
OR binding to a ligand to alter
which bacteria have OmpC and OmpF
Gram -
outer membrane, so they must have outer membrane protein cores
OmpF
opening of lager pore
allows more to flow through
opening of a smaller pore to allow less diffusion is which of the Omp?
OmpC
Regulation of Omp
depending on environment, upregulation/rexpression of 1 and inhibition of expression of other
Mechanisms of expression of Omps
micro RNA (OmpF, binds)
2 component systems (sensor kinase – senses environment -gut or nah- which then causes phosphorylation of response regulator (ompR))
OmpR
response regulator (protein 2)
EmpZ
sensor kinase of OmpC/OmpF system
how do you determine if clockwise or counter clockwise
methylation or ligand binding
ligand binding > methylation
spinning =
run, so moving counter clockwise
methylation >
attractant has already bound, and used up what’s there
tumble, stimulates clockwise rotation
CheA
phosphorylates
sensor kinase
to continue on a run, not going to spin
CheA is NOT phosphorylated
When high [attractant] proteins are:
CheR= methylated
CheA= phosphorylated
CheR
adds methyl groups
CheB
removes methyl groups
promotes continuation of run
