Environmental stress response Flashcards
What causes stress?
- starvation
- acidity
- hyperosmolarity
- high or low temp
What is osmotic balance?
- mechanosensitive channels protect cell from sudden decreases in external osmotic pressure
when do channels open for osmotic balance?
- under conditions of hypoosmotic stress and allow internal solutes to rapidly exit
What is a batch culture?
- finite amount of nutrients
- each cell has own life cycle
What is a lag phase?
- adjustment to new media with no growth
What happens during exponential growth?
- nutrients run out, vulnerable as all energy goes toward growth
What is the stationary phase?
- more focused on survival (more tolerant)
- growth = death
What is the death phase?
- death>growth
- some feed off of dead neighbors and get little blips of nutrients
Cells entering stationary phase more ______ to environmental stress
resistant
what are toxic oxygen products?
- hydroxyl radical
- superoxide radical
- hydrogen persoxide
What enzyme is required to dissociate toxic oxygen products?
- superoxide dismutase or catalase
What happens during heat-shock?
- heat-shock proteins (Hsps) synthesis increases relative to synthesis of other proteins
Hsps play important roles in ____ at all temp
growth
What do hsps function as?
- repair/eliminate proteins that are damaged by heat stress
What is RpoH responsible?
- heat-shock protein synthesis; mutants deficient in RpoH cannot grow above 20 degrees C
What are the roles of Hsps for minor heat shock response?
- folding of newly synthesized proteins AT ALL TEMP
- export of proteins AT ALL TEMP
- refolding of misfolded polypeptides
- proteolysis of improperly folded/abnormal proteins
How do bacteria repair damaged DNA?
- photoreactivation
- nucleotide excision repair
- recombination
- base excision repair
- GO system
What is photodimerization?
- exposure to light (UV exposure blocks replication)
- mismatches base pairs (gaps in DNA)
- chemical modification of bases
What blocks DNA replication?
- photodimerization of pyrimidines from excitation of DNA by UV radiation
What is photoreactivation?
- light repair
- gene codes for photolyase
- dimerization reversed following absorption of 300-500nm
What does light energy do during photoreactivation?
- cleaves dimers into monomer to restore coding properties
What is photolyase?
- reverses dimerization
- 1 part damages, the other is used to fix
What is nucleotide excision repair?
- endonuclease cuts nucleotides awat on either side of dimer
- SS gap filled by DNA polymerase I and sealed by ligase
- snips and fills gap
What is the SOS response?
- cell response to distress signal by DNA damage when RecA binds to ssDNA (results from bypass in replication of damaged DNA)
- allows replication around damage
