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48 Cards in this Set

  • Front
  • Back
Before ingestion, intestinal pathogens often reside in water having what four characteristics?
1. low temp
2. low ionic strength
3. near neutral pH
4. low conc. of organic material (low nutrients)
Once injested, pathogens must adapt to what five conditions found in the body?
1. higher temp
2. high osmotic pressure
3. high and low pH
4. low O2
5. abundant nutrients
What happens to the iron in the cell when the cell is infected?
Cell sequesters all the iron
To survive do pathogens have to rapidly express adhesins? Why or why no?
Yes, to allow for colonization in the intestine.
Virulence factors are found in large areas of a chromosomes called a "pathogenicity island". Would a nonpathogenic relative of the same pathogen have this chunk of DNA?
No, it would be missing
Multicistronic operon
bacteria's unit of transcription that includes more than one cistron
gene - sequence of DNA that encodes a polypeptide
Multicistronic mRNA
mRNA that results from transcription of a multicistronic operon occuring only in prokaryotes
In bacteria, how many promoters are needed for many genes?
One promoter
RNA polymerase - a biological machine that transcribes DNA into mRNA
Sigma factor
a subunit of the RNAP that specifically recognizes and binds to the promoter region
cRNAP (core) + sigma =
= holoenzyme

What is the product of the RNAP/DNA interaction?
Formation of a closed complex

Once RNAP binds what happens?
DNA opens to form the open complex and sigma falls off. This strand separation allows for synthesis of a mRNA strand complementary to DNA sense strand.
When does transcription elongation of mRNA stop?
When RNAP encounters a termination signal

Cells regulate transcription at initiation.
What does the frequency of initiation depend on?
The ability of the RNAP to bind the promoter.
sits next to the RNAP on the promoter sequence
There are three types of regulator proteins to control frequency of initiation of virulence factors:
repressors, inducers, activators. Explain and give examples of each.
Repressors - binds to operator which overlaps promoter prohibiting RNAP binding
Inducer - binds to repressor, changing confirmation of that protein so it can no longer bind DNA, ex. Lactose

Activator- increase RNAP's ability to bind the promoter, ex CRP
The Lac operon is found in E.coli, acting to regulate metabolism of lactose - what is the relationship between glucos and cAMP in the lac operon?
In conditions of high glucose there is low cAMP and then no CRP to help RNAP bind.
How do cAMP and CRP work together in the lac operon?
They bind to eachother and this will bind to DNA and increase chances of closed complex formation and transcription occuring.

What five interactions enhance transcription initiations?
1. sigma with DNA (promoter)
2. DNA : alpha CTD
3. sigma factor : alpha CTD
4. CRP : DNA
5. CRP : alpha CTD
Does stabilizing the closed complex enhance or inhibit transcription?
Is the sigma factor involved in both the open and closed complexes?
Is cAMP:CRP involved in both the open and closed complex formation?
No, just in the closed complex formation.
What do regulons do?
Regulate large groups of independantly controlled operons to adapt to environment. They turn some operons on and others off.
Compare Vibrio Cholerae to Salmonella Typhimurium:
Vibrio Cholerae:
Life threatening diahhreal disease (3rd world) that is caused by a highly motile, unflaggellated, gram -, extracellular pathogen that colonizes in the upper small intestine and produces and excretes toxins which disseminate in watery diarrhea

Salmonella Typhimurium: Am intracellular bacterium that causes a self-limiting but severe case of diarrhia and fever and can also get into the blood. The bacterium invades into the Peyer's patches of the intestine and gets into M-cells and macrophages to produce toxins.
Explain the five steps that must happen to cause V.Cholerae disease:
1. has to be ingested via contaminated food
2. survive passage through the gastric acid barrier of stomach
3. colonize in the upper SI
4. produce and excrete toxin
5. disseminate in watery diarrhea
If a V. Cholerae is not infected with a CTX phage will it cause diarrhea?
Describe the ctxA operon of a CTX phage and its mechanism.
ctxA - is cleaved to yield active A subunit which catalyzes a Gs alpha to ribosylates ADP.
- Gs alpha activates adenylate cyclase
- AC activation increases cAMP levels to increase PKA
-PKA phosphorylates proteins that are involved in ion transport
-these proteins cause water to leak into intestinal lumen
Describe the ctxB operon of a CTX phage and what two things it is required for.
ctxB - required for secretion of A1 toxin out of the bacterial cell. And it is required for interaction with host cell surface receptor, GM1 glycoprotein.
How many A and B subunits are there in CTX operon?
1 A and 5 B
Virulence factors:

Would a nonmotile or hypermotile mutant increase virulence?
It would decrease
Within the CTX phage are flaggellar genes and cholera toxin genes for colonization and toxigenicity expressed together?
NO! Flaggellar (TCP: toxin colinization pilus) first than cholera toxin genes for colonization (ACF: accessory colonization factor) after flaggellar have been turned off.
Compare the regular Vibrio Cholerae with the strain used in vaccines:
Vaccine strain was determined to be less reactogenic and less motile
Mutations in what two genes in Vibrio Cholerae could cause reduced colonization?
ACF (accessory colonization factor) and TCP (toxin colonization pilus)
Where are acf and tcp genes located on the genome? What is this region called?
They are located on a pathogenicity island called the TCP-ACF element
What regulated the toxicity of Vibrio Cholerae?
the ToxRS virulence regulon
What is Tox R?
A protein that acts as the global virulence regulator product of the tox R gene and spans the cytoplasmic membrane of the Vibrio Cholerae
What is Tox S and what does it do?
It is a protein that acts as an environmental sensory product to the tox S gene, also spaning the cytoplasmic membrane. It activated Tox R
What regulates the transcription of the toxRS operon of Vibrio Cholerae?
What genes are turned on/off when:

Temperature is low outside host?
Tox RS: ON - gets transcribed
Tox R and S is synthesized and incorporated into the cytoplasmic membrane and waits to receive a signal.
What genes are turned on/off when:

High temp inside host's upper GI?
Tox R and S not synthesized, old proteins still present in membrane.
What genes are turned on/off when:

High temp inside host's intestine?
Tox S receives a signal unique to intestinal environment. Tox S activates Tox R. Tox R binds to the TCP-ACF element in DNA and activates TCP-ACF transcription. This causes the production of Tox T. The Tox T protein then binds to the site upstream of the promoter helping RNAP causing amplification of the Tox T being made.
Which Tox, Tox S, R, or T, is autoregulated?
Tox T
Tox T can control the production of itself - what else does Tox T control?
Tox R regulon genes including TCP and ACF (turning them on).
Would a nonpathogenic vibro cholera relative have the chromosome toxRS operon?
Yes, just not the pathogenicity island

What three things does Vibrio Cholerae virulence depend on?
1. the ToxRS operon located within the chromosome
2. the pathogenicity island of TCP-ACF element that also includes Tox T
3. The CTX phage carrying ctxAB from a temperate or lysogenic bacteriophage