L 20 virulence and gene regulation

Question 1

VIRULENCE FACTOR

Answer 1

any bacterial property required for entry, growth, or survival in a host (but not required for life in lab)

examples:
capsule - inhibits killing by complement
adhesins - permit adherence to host cells
acid tolerance factors (ASPs) - adapt pathogen to stomach
enzymes - synthesize unavailable nutrients

Question 2

VIRULENCE GENE

Answer 2

any gene that encodes a virulence factor

5 - 10 % of Vibrio or Salmonella genes

often located on mobile genetic elements (plasmids or phage)

or in

pathogenicity islands* (large, localized regions of chromosome missing in related non-pathogens)

Question 3

cistron

Answer 3

a sequence of DNA that encodes a polypeptide.

old term for gene

Question 4

operon

Answer 4

a unit of transcription that includes more than one cistron.

Question 5

a typical operon contains

Answer 5

a promoter, an operator, cistrons and a terminator

Question 6

promoter

Answer 6

the site at which RNAP binds

Question 7

sigma

Answer 7

sigma, a subunit of RNAP that specifically recognizes and binds the promoter (TATAAT or TTGACA). falls off after elongation begins (involved in open and closed confirmation) has homologs in archea and eukaryotes

Question 8

closed complex.

Answer 8

The product of the RNAP/DNA interaction

Question 9

Open complex

Answer 9

once bound RNAP causes the double strand to open making the open complex

Question 10

primary transcription regulation

Answer 10

at initiation

Question 11

Repressor

Answer 11

binds the operator, a site located close to or overlapping the promoter. The overlap prohibits binding of RNAP to promoter. (steric hindrance)

Question 12

inducer

Answer 12

a small molecule that binds the repressor, changing that protein’s conformation so that it can no longer bind DNA

Question 13

lac operon in the presence of glucose & low cAMP

Answer 13

example of repression: repressor is bound to the operator blocking the promoter

Question 14

lac operon when glucose is absent and therefore cAMP is high AND lactose is present

Answer 14

1. lactose (inducer) binds the repressor preventing the repressor from binding the operator
2. cAMP (co-activator) bind CRP (activator)
3. cAMP-CRP interacts with RNAP increasings its ability to bind the promoter
4. the gene is transcribed (lac mRNA is made)

Question 15

activator

Answer 15

interacts with RNAP increasing the ability of RNAP to bind the promoter. Increase the stability of the closed complex

Question 16

what affects the probability that transcription will occur?

Answer 16

The probability of transcription initiation increases
as the stability of the closed complex increases

activators increase stability
repressors decrease stability

Question 17

polymerase core enzyme

Answer 17

2 alpha, 1 beta and 1 beta* subunits

highly homologous to all RNA polymerases

Question 18

sigma + core enzyme

Answer 18

holoenzyme

Question 19

CRP

Answer 19

activator in lac operon, it is a dimer and when bound to cAMP it interacts with DNA and the alpha-CTD subunit involved in closed complex formation

Question 20

alpha-NTD

Answer 20

helps to assemble the core enzyme

Question 21

alpha-CTD

Answer 21

connected to a-NTD by a flexible linker, binds DNA, involved in closed complex formation, interacts with sigma involved in open formation

Question 22

regulons

Answer 22

a group of operons (aka global control system) subject to the control of a common (or global) regultor

Question 23

how does a regulon work?

Answer 23

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.