Virulence of Mechanisms of Gene Regulation Flashcards
Before ingestion, intestinal pathogens often reside in water at
- low temperature
- low ionic strength
- low concentration of organic nutrients
- neutral pH
After ingestion, intestinal pathogens must adapt to
- higher temperature
- higher osmotic strength
- low pH
- high pH
- bile salts
- lack of oxygen and abundant nutrients
- sequestration of iron by host
To survive this journey, the pathogen must rapidly express a variety of gene products:
-proteins that help tolerate low pH of stomach
-flagella and chemotaxis proteins
-for migration to suitable niche
-adhesins that permit colonization
-toxins & invasins to elicit disease
iron chelators (siderophores) to scavenge for iron
VIRULENCE FACTOR
- any bacterial property required for entry, growth, or survival in a host
- —examples:
- capsule - inhibits killing by complement
- adhesins - permit adherence to host cells
- acid tolerance factors (ASPs) -
- adapt pathogen to stomach
- enzymes - synthesize unavailable nutrients
- 5 - 10 % of Vibrio or Salmonella genes
- often located on mobile genetic elements (plasmids or phage) or in pathogenicity islands*
pathogenicity islands
-large, localized regions of chromosome missing in related non-pathogens
cistron
a sequence of DNA that encodes a polypeptide
Bacteria organize their genes in
multicistronic operons.
operon
-a unit of transcription that includes more than one cistron.
multicistronic mRNA
-the mRNA that results from transcription of a multicistronic operon
The typical operon
promoter, an operator, cistrons and a terminator
promoter
the site at which RNAP binds
sigma
a subunit of RNAP that specifically recognizes and binds the promoter
closed complex
The product of the RNAP/DNA interaction
open complex.
Once bound, RNAP causes the double strand of DNA to open
how do cells regulate transcription
- Cells regulate transcription primarily at its initiation
- They make the decision to initiate or not by setting the frequency of initiation
- The frequency of initiation depends upon the ability of RNAP to bind the promoter
repressor
- binds the operator, a site located close to or overlapping the promoter.
- The overlap prohibits binding of RNAP to promoter
inducer
-a small molecule that binds the repressor, changing that protein’s conformation so that it can no longer bind DNA
activator
-interacts with RNAP, increasing the ability of RNAP to bind the promoter
co-activator
- (cAMP) binds activator
- increasing ACTIVATOR binding affinity
The probability of transcription initiation _____ (incr/decr)
as the stability of the closed complex ____ (incr/decr)
- increases, increases
- activators increase stability
- repressors decrease stability
regulon (a gene network) chain of events
1) through the action of some sensor molecule, a cell senses a stimulus;
2) sensor signals to activate/deactivate a regulator;
3) regulator binds to several operons;
4) binding turns some on & some off;
5) gene products respond to the original stimulus; &
6) gene products exert feedback control on their own expression.
most of the regulation of gene expression comes from…
-getting the RNA polymerase to bind long enough to get transcription
when glucose levels are high, cAMP levels are ______
low
Glucose present / cAMP absent = _____
repression
glucose absent/cAMP present
lactose (inducer) present = ______
INDUCTION
interactions that enhance transcription initiation
1) sigma /DNA (promoter)
2) DNA/alpha-CTD
3) sigma/alpha-CTD
4) CRP/DNA
5) CRP/alpha-CTD
