Lecture 6 Flashcards
(25 cards)
RpoS
Activated during stationary phase and controls 10% of genes in E.Coli
RpoS
Stress induced sigma factor which transcribes the housekeeping genes
MazEF Complex
an antitoxixn gene and a toxin gene hat combine resuting in a neutralized toxin. mediated death pathway can act as a defense mechanism that prevents the spread of bacterial phage infection, allowing bacterial populations to behave like multicellular organisms.
What happens to MazEF complex during stationary phase?
The two genes are not synthesized as much and some cells become poisoness instead of neutralized
Bacillus and Clostridium form endospores which do what?
Provide strong resistence to chemicals, ionizing radiation and heeat
How are spores produced in vegetative cells?
there is a nutrient stress which creates low concentration of SpoOA-P, genes with high affinity to SpoOA-P are activated to create some cells with immunity to toxins and some cells that are toxins. The Toxins kill cells with low SpoOA-P and dead cells are lysed releasing nutrients. The cells with high SpoOA-P concentration now form spores
What mutation do streptomycin-resistant cells have?
A heritable change in DNA in the gene rpsL
Describe the streptomycin-dependent mutation discussed in lecture?
Mutated S12 prevents strep. from binding, the correct codon-anticoon interaction takes place
How can you isolate streptomycin-resistant mutants by selection?
Plate the cells on plate with streptomycin and see which ones can grow (These are the resistant cells)
Is the mutation heritable?
Yes in the absence of selection
What does auxotrophic mean?
THe bacteria has a mutation which keeps it from making a certain amino acid
What will plates look like in serial dilution in mutations are INDUCED by streptomycin?
similar number of mutated colonies on each plate as the first time you plate them
What will plates look like in serial dilution if mutation are random and pre-existing?
greater variation than before in the number of resistant colonies per plate
MutHLS protein complex function?
Recognizes changes in helix due to base pair mismatch (in euks if you have a mutation here you have higher probability of cancer)
How does MutHLS find bad DNA?
It recognizes older DNA (because it is methylated) an knows that the old DNA is good so it looks for places were the DNA is unmethylated
How does MutHLS actually repair the DNA?
It makees a nick in the DNA and unwinds it at the unmethylated places and then DNA polymerase fills the gaps in. DNA ligase then fills the gap
How do mutations usually occur?
When the cell is attempting to repair DNA damage
How does UV damage the DNA?
By forming thymine-thymine dimers causing a distorted DNA backbone
Light Reactivation repair system
Photolyase enzyme easily reversed the thymine-thymine dimer
Excision Repair system
UvrABC nuclease and UvrD helicase remove DNA containing damage to create single stranded “patch”. The patch is then repaired by DNA poly 1 and ligase
What is unique about the W3110 uvr phr strain of E.Coli?
The E.coli has inactivated photolyase system and inactivated excision repair mechanism
what happens when W3110 is exposed to UV?
MANY cells die because they can’t be repaired and the cells go into SOS response which results in high rate of mutations
What does the SOS response do?
It stops the LexA repressor protein from working resulting in inactivated genes
What happens to DNA poly 3 and what replaces it?
It can no longer replicate but Poly V takes its place
