Green 16 - Growth Regulation Flashcards
Gene expression is often regulated by ____ ____.
Growth rate
Which 2 regulatory proteins are involved in the stringent response within E. coli and what are each triggered by?
SpoT - limiting P, iron, osmotic shock
RelA - living amino acids
Describe, with the aid of a diagram, how RelA brings about the expression of stress response genes.
RelA converts GDP/GTP + PPi -> pp(p)Gpp
ppGpp build up sensed by DksA and brings it to RNAP
RNAP then, with sfS, allows the expression of the stress response genes
Describe how a limiting phosphate conc brings about a change in gene expression via the stringent response.
Limiting P sensed by SpoT (because no exponential growth - this is what SpoT senses)
Reverse reaction of ppGpp -> GDP + PPi is inhibited
Build up of ppGpp - recognised by DksA
RNAP transcribes the IraP protein
IraP binds to RssB (normally sequesters RpoS (sfS) and directs it to ClpXP for degradation)
SfS is free to activate the stress response genes
Describe how the steady state is maintained via the stringent response.
RelA and SpoT work together -> ppGpp
ppGpp stimulates RNAP to transcribe IraD
IraD + RssB
SfS Is free. unsure what the function of this is now
This system figured out by mutational analysis NOT nutritional studies
Give 3 examples of how the stringent response is involved in pathogenesis.
- Legionella response to nutrient depravation. nutrient starvation -> high concn of ppGpp. Nutrient rick = low conc of ppGpp
- Salmonella response to the production of host CAMPs (antimicrobials). helps to defend against them
- another example = escape from a phagosome inside host and initiate replication
Why, when nutrient concn is low, are many catabolic enzymes made?
At low nutrient concn = low C sources
Low concn of a variety of C sources become available therefore need a variety of catabolic enzymes to exploit these C sources
What is catabolite repression?
Catabolite repression allows E. coli to use its preferred C source first (glucose)
Uses the catabolite glucose to repress expression of enzymes involved in breaking down of other carbohydrates
Explain how the phosphotransferase system is involved in the regulation of the lac operon expression.
PTS system transports glucose from outside the cell -> cytoplasm
when glucose is present, the PTS is unP (as glu > glucose-6-P when leaves the transporter)
inactive Adenylate cyclase - no cAMP production
when no glu present, PTS is P , active AC
AC converts ATP -> cAMP
@ the lac operon, cAMP binds to CRP (tf - cAMP receptor protein)
binds @ promoter and recruits RNAP
when we have high glu and no lactose, lacI repressor bound @ operator to repress transcription
when we have lac and low glu, Allolactose (inducer) binds to and removes the repressor to allow transcription
expression of genes to use lactose as energy source
What other molecule, that is not transported by the PTS, involved in cAMP synthesis and partitioning of the proteome?
a keto glutarate - inhibits AC
What are the roles of a keto glutarate in the cell?
Energy generation in the Krebs cycle
Production of Glu in N assimilation
____ metabolism is _____ proportional to _____ rate (in the absence of futile N cycling).
Anabolic
directly
growth
What happens to anabolism when the growth rate is low?
Rate of anabolism decreases, the proteome shifts to producing more catabolic enzymes to exploit the limited nutrients
Give the process of N cycling, with a keto glutarate.
a keto glutarate -> Glu -> Glu -> N recycling back to aKG
What occurs when there are high rates of catabolism?
Low anabolism
high concn of aKG
AC inhibited therefore low cAMP
barely any expression of catabolic genes (high cat = high source of C)
