Stationary phase - stress response L8 Flashcards
how do bacteria effect protein production
Bacteria activate and induce systems to make new proteins to carry out new functions switch off systems don’t need to adapt to environment
how are bacteria grown in a batch culture
Cells are inoculated into a sterile broth, incubated under permissive growth conditions
when does cell mass increase in batch culture growth
Cell mass increases rapidly as cells enter exponential phase of growth, then reach stationary phase
when does cell mass stop increasing
until conditions inside flask limited
why is it important for single cells to monitor nutrients
needs to be able to monitor level of nutrients and respond that will run out - no point continually running processes if these processes can’t run to completion, need to start to ‘turn things down’
when do toxic products start to accumulate in batch growth, effect
Will get a change in environment, pH tends to drop, oxygen lowers, toxic by-products will start to accumulate– protect against harsh conditions
Cell growth stops, and cells go into a dormant state
what is the stringent response
Fast cell growth requires high levels of protein synthesis, so cell needs lots of ribosomes
Under starvation conditions, when amino acids levels are limited, cell reduces number of ribosomes - would use a lot of energy to make all proteins that wouldn’t be used
how is regulation achieved
Regulation achieved by stringent factor acts with GTP in synthesis of ppGpp
stringent factor (RelA protein)
how can ppGpp be synthesised
Carbon limitation can also cause synthesis of (p)ppGpp
what does ppGpp do
down regulates the rRNA synthesis of genes = fewer ribosomes being assembled
- ppGpp down regulated tRNA synthesis
Everything in the cell is being down regulated
ppGpp and protein production
signal to RNA polymerase to stop making proteins, needs to switch off transcription – need to turn things down till have nutrients available again
what is ppGpp
an alarmone
how is ppGpp an alarmone
involved in the stringent response in bacteria, causing the inhibition of RNA synthesis when there is a shortage of amino acids present
what causes increased ppGpp
nutritional stress
how does transcription reprogramming occur
ppGpp will bind to the RNAP sites, causes “reprogramming” of transcription
what transcription changes occur during reprogramming in E.coli
results in changes in ~700 genes now changed in their gene pattern of regulation
- Most of them are down regulated – rRNA (to make ribosomes, fatty acids for membrane synthesis), some specific stress genes are up-regulated
how do bacterial cells in stationary phase differ to those in growing cells
- shorter and rounder (if rod shaped) (spheres would be smaller)
- altered metabolism (recycle molecules from other things)
- change in membrane and cell wall structure as defines shape
- increase resistance to number of different stresses e.g. starvation, osmotic shock – cell prepared self for ‘survival mode’
what are sigma factors like
interchangeable, control which sets of genes are expressed (differential expression)
what is core polymerase
enzyme that makes RNA in cell carries out transcription, when it binds to a promoter – core polymerase is directed where to start transcription by the sigma factor
where will the sigma factor bind to
-10 -35 motif
what are the motifs in bacteria
motifs differ in different sigma factors
what must a bacteria have to be expressed all the time
sigma 70 motif, can switch on others when they’re needed
how may names does each sigma factor have
two as discovered in two ways
what is the primary site of control of prokaryotes
transcription
