Stress Flashcards
What is stress
Any deviation from optimal growth conditions that result in a reduced growth rate
How do stress response systems interact together
By a complex of global regulatory networks
Types of stress
Osmotic
Oxidative
PH
Thermal
Nutrient
Osmotic stress happens when
Sudden change in solute conc
Hyper out
Hypo in
Osmoregulation is
A process to minimise cell damage
4 ways of osmoregulation
Controlling ions efflux and uptake
Accumulation of osmolytes
Osmosensors
Biofilms
Osmolytes func and who
Proline, betaine , trehalose
Allow cell to retain water
Protect proteins from denaturation or aggregation
Reduce ROS
Osmosensors are and lead to
Proteins that detect osmotic changes
Activation of some genes expression and metabolic adjustments
Biofilm in osmotic stress
Physical barrier
Gradient of osmotic conditions
Metabolic interactions
Genetic adaptation like plasmid transfer
Oxidative stress is
Due to
Imbalance between ROS and antioxidant mechanism
Disturbance in cells redox state
Aerobic metabolism or exogenously from enivironment
The ROS
Superoxide anion o2-
Hydrogen peroxide h2o2
Hydroxyl radical HO’
How ROS transfer to each other
O2»_space; O2- by oxidase
O2-»_space; H2O2 by superoxidase dismutase
H2O2»_space; HO’ by peroxidase, most dangerous
2 reactions
Haber Weiss»_space; O2- + H2O2 > OH- +OH’ +O2
Fenton»_space; fe2 + H2o2»_space; Fe3 +OH ‘ + OH-
How to regulate oxidative stress
Scavenger enzymes, no enzyme for hydroxyl
Redox signals by redox sensitive regulators
The overall reaction
Oxygen to superoxide by oxidase
Then to hydrogen peroxide by SODs then to water by catalase or hydroxyl radical by peroxidase
The genes of regulation in oxidative stress
SoxRS, respond to superoxide in all
OxyR respond to hydrogen peroxide in negative
PerR respond to hydrogen peroxide in positive
Transcriptional activators, upregulates genes concerned with antioxidative defense and repair mechanisms
PH and acid tolerance mechanisms
PH homeostasis
Restriction of proton permeation
Consumption of protons
Alteration of cell membrane
Biofilm
Metabolic regulation
Protection and repair of macromolecules
What are repair mechanisms in oxidative stress stimulated by redox sensitive regulators
Aa biosynthesis
Cell wall synthesis
Ph homeostasis
Restriction of proton entry
Proton consumption
Proton pumps to pump protons out and import potassium and sodium to counterbalance acidification by antiporters
Less permeable membrane and modulated channel size
Consune excess ex urease combines with H+ to produce ammonia to neutralise the pH in heliobacter pylori
Proton pump vs antiporter
Low pH vs High pH
Proton pump is unidirectional for protons
Antiporter is bidirectional for a range of ions
Low ph is high conc of protons, high ph is the opposite
Altering membrane
Biofilm in pH
Metabolic
macromolecules repair
Change in integrity, fluidity and lipid composition to protect from proton influx
Protect and shield by extracellular matrix and interactions
Glycolysis increase by 70 percent
Chaperons protect misfolding and inhibit death signals
Why glycolysis increase with low pH
ATP production and protons consumption
And fixing the NADH/NAD+ ratio
To compensate the damage
What do some bacteria do to stabilise proteins and prevent their denature at low ph
Acid shock proteins
High temp leads to
Low leads to
Denaturation
Disruption of membrane
DNA damage
Metabolic changes
Reduced metabolism and ice formation
Mesophiles…leads to heat shock and
…leads to cold shock and code for..
40
15
Chaperons
The signal controlling heat shock response is..HSP known as…help in..under
Types according to molecular weight
Unfolded proteins
Chaperone
Proper folding
Heat stress
HSP70, HSP90, smallHSP
HSR phases, induction
Induction, in stress but not lethal signal activated transcription factor to increase heat shock genes to overproduce heat shock proteins.
HSR adaptation
Adaptation, protein structure stabalized and not unfolded, misfolded are not aggregated, refolding of misfolded or denatured, correct folding of new proteins
HSR,Steady state
Balance between protein synthesis and degradation, sustained as long as stress us present
Response to nutrient limitation
Starvation
Stringent
Starvation aim
Adapt till nutrients conditions improve
Starvation steps 1
Express higher nutrient utilization systems to scavenge nutrients
Degrade glycogen stored for energy, release enzymes to degrade complex molecules and gain nutrients from the environment
Starvation steps rest
DNA condensation
Ribosome degradation
Endospore
Altering amounts and types of lipid components
Energy saving
Why degrade ribosomes
Who can form endospore
energy consuming processes are
To gain nutrients
Bacillus and clostridium
DNA replication and cell division
Bacteria in starvation can increase…in membrane or adjust its…by…to make the membrane more…and maintain…
Unsaturated fatty acids
Thickness
Changing length of fatty acid chains
Fluid
Integrity
Stringent response
Depletion of amino acids, growth stops them metabolism adjustments to maintain protein synthesis accuracy
How stringent response
Low DNA replication
Low RNA accumulation esp stable ones r and t
Low biosynthesis of carbs, lipids, peptidoglycans
Shut down of transport of macromolecule precusors
