Temperature stress and Osmoregulation L9 Flashcards
what happens when temperature changes
chemical and enzymatic reactions change
- faster rates at higher temperatures
- slower rates at lower temperatures
growth rates change
what is an arrhenius plot used for
describe the relationship between growth rate and growth temperature
effect of temperature on microbes growth
Can cool microbes to a point where stop growing, if warm them up again will grow again
what occurs at minimum growth rate
membrane gelling
transport processes slow so growth cant occur
what occurs between minimum and optimum growth rate
enzymes and reactions occurring at increasingly rapid rate
what occurs at optimum growth rate
enzymes and reactions occurring at maximal possible rate
what occurs at maximum growth rate
protein denaturation, collapse of cytoplasmic membrane, thermal lysis
in frozen water what grows
nothing as microbes need water to grow
what is a psychotroph
organism that has an extended growth range
can adapt to extremes of temperature by changing cellular processes
what does each single stress response induce
specific set of stress proteins
what are stress responses controlled by
alternative sigma factors
what happens if stress response genes induced
helps cell repair any damage and adapt to new temperature
what happens to the cell after heat shock occurs
major damage - proteins denatured
macromolecular complexes dissociate e.g. ribosome
individual cell proteins denatured
how does cell respond to high temperature stress
inducing synthesis of heat shock proteins (Hsps)
what are heat shock proteins function
role in getting proteins to fold correctly
how do proteins fold
not all proteins fold spontaneously inside bacterial cells
~30% need assist
what do proteins that cant fold need
chaperone
heat shock proteins are chaperones
what are the two major groups of heat shock proteins - chaperones
20% need DnaJ and DnaK
10-15% also need GroES and GroEL
what happens in response to heat shock
needs more heat shock proteins and other new gene products
what prevents heat shock gene production
DnaK normally binds to sigma 32 and prevents it binding to promoter to express heat shock genes
what happens to the unused sigma 32
targeted for degradation by protease FtsH
what happens when heat shock occurs
DnaK now needed in cell to bind to denatured proteins
releases sigma 32 and heat shock proteins induced
when is sigma 32 made
sigma 32 always present in cell
what happens to DnaK under normal conditions
DnaK targeted, picked up by DnaJ sent to FtsH, gets broken down
what happens when DnaK and DnaJ release sigma 32
can interact with RNAP and switch on heat shock genes
how does osmoregulation effect the cell
Turgor pressure controlled by adjusting total osmotic solute pool
Solute accumulation /efflux is central to control
Many different cellular systems involved
what is the most abundant cation in bacteria cytoplasm
potassium
when does potassium concentration increase
following hyperosmotic shock
what effects potassium concentration
adaptive process so must be reversible
what causes potassium influx
response to increasing osmolarity = trk, kdp
what causes potassium efflux
response to reducing osmolarity = kdpB, kdpC
what operon controls potassium efflux
Encoded by kdpFABC operon
what REGULATES potassium efflux
KdpD and KdpE = “2 component response regulator”
where is KdpD
inner membrane protein of E. coli
what is KdpD
autophosphorylating sensing protein
cytoplasmic regulator protein
what happens in Kdp regulation
periplasm proteins change shape in response to potassium concentration
- if potassium conc low = protein on outside in periplasm changes shape = protein picks up a phosphate group from ATP = autophosphoprylation
phosphate transferred to KdpE protein (in cytoplasm)
KdpE-phosphate binds to kdpFABC operon promoter
when is the kdpFABC operon activated
Switch on in response to potassium depletion outside cell
wat happens in kdpFABC operon when high enough potassium
signal goes away
reset system in response to environment
what are porins function
allow diffusion of small polar molecules across OM of Gram-negative bacteria
Allow bulk transport across lipids
what are the two major porins produced
OmpF
OmpC
how do the porins differ
OmpF = 1.16 nm pore allows rapid diffusion of molecules OmpC = 1.08 nm excludes bile salts & allows slower diffusion of molecules
In human gut where high solute concentration present which omp is made
OmpC produced -bile cant get through
Small regulatory proteins involved in controlling this switch
what is the pro of small porins
bile salts can’t get through
what is the con of small porins
slow diffusion of molecules
what is EnvZ
sensing protein
what happens in low osmolarity in porin regulation
outside gut = low osmolarity Phosphate group transferred EnvZ in inner membrane from regulatory protein OmpR ompR phosphate goes towards C OmpR-P conc always low will only bind to ompF OmpC porin not activated
what is IHF
Small DNA binding protein known to be involved in the regulation of many genes
what is IHF made of
consists of 2 subunits (α and β)
what does IHF do
binds to specific consensus sequence in promoters 5′-TATCAA-3′ and 5′-TTG-3′ pulls DNA round in really tight curve IHF can bind and pull it round change shape to stop promoters bind
what happens in high osmolarity in porin regulation
inside gut = high osmolarity
Direction of Phosphate transfer is now towards OmpR
[OmpR-P] increased and can now bind to weak promoter binding sites
ompF repressed by DNA bending of promoter induced by IHF binding
ompC porin activated by OmpR-P
what are stress responses for
required for the survival of individual cells
Cell has to change itself to match the change in the environment
how is the role of alternative sigma factors identified
identified in controlling sets of genes (regulons) linked to different stress responses
what are examples of stresses and different regulatory systems
General stress (RpoS) Starvation “stringent” response (ppGpp) Heat shock (DnaK, σ32) Osmotic shock (K+, compatible solutes, Omps, 2-component response regulators)
what regulates which omp porin is made
regulated in response to changes in the environmental conditions
