Bacterial Replication and Transcription 5.3 Flashcards
Positive control of transcription is implemented by?
activator proteins
activator proteins bind to? enhance? allosterically modified by? does NOT bind unless?
bind to activator binding sites
enhance transcription
Activator protein activity is allosterically modified by inducers
Activator protein does not bind unless inducer is present
Activator binding site is upstream or downstream from promoter
upstream
How does an inducer affect positive control activator proteins?
promotes the binding of the activator protein to the activator binding site, and thus stimulates transcription
In the case of maltose utilization, what is the inducer? important for what?
maltose
*This system is pertinent in regulons
What is ‘regulon’?
term for genes of a pathway that are spread throughout the bacterial chromosome
Explain catabolite repression?
- global regulatory mechanism
- helps cells make the most efficient use of different carbon sources
- cells will use glucose first
due to catabolite repression, glucose or lactose is used first in a diauxic growth?
glucose
*As the glucose is depleted, the repression is lifted and production of enzymes for catabolism of the second nutrient is started
diauxic growth
bacteria exhibit this when there are two energy sources available
The lac operon is controlled by?
1) catabolite repression
2) its own specific regulatory system
explain lac operon catabolite repression complex
1) requires cyclic AMP to bind to catabolite activator protein (CAP)/ cyclic AMP receptor protein (CRP)
2) CAP/CRP cyclic AMP complex binds upstream of the promoter for the lac operon and recruits RNA polymerase
In order for Lac gene transcription to occur, cyclic AMP must bind to?
CAP
In cells growing on glucose the level of ____ is low and _____ is not activated
cyclic AMP is low (due to unphosphorylated Enzyme IIA of phosphotransferase system) and CAP is not activated
As glucose is used up cyclic AMP? What happens to CAP?
increases (due to phosphorylated Enzyme IIA of phosphotransferase system) and CAP is activated
Prokaryotic signal transduction
1) typically involves?
2) a membrane-integrated?
3) a cytoplasmic?
4) activity of response regulator depends on?
1) involves two-component regulatory systems
2) membrane-integrated sensor kinase protein
3) a cytoplasmic response regulator protein.
4) depends on its state of phosphorylation
sensor proteins are often? do what?
often kinases (sensor kinase) or associated witha kinase *transfers the phsphate to the response regulator protein
response regulator protein is typically?
a DNA binding protein that acts as a repressor in the PHOSPHORYLATED form
kinases do WHAT? like all the time?
phosphorylate stuff! phosphorylate target cytoplasmic proteins OR itself via autophosphoylation in response to environmental conditions
Quorum Sensing definition?
a process by which cells are able to detect the accumulation of a released signal and then change their behavior when the signal concentration exceeds a threshold level
Why is Quorum Sensing important for cells?
1) allows cells to survey their environment for cells of their own kind.
2) able to sense population size.
How can a cell sense population size in Quorum Sensing?
involves the sharing of specific small molecules. Once a sufficient concentration of the signaling molecule is present, specific gene expression is triggered
What is a common quorum sensing inducer?
AHL
Quorum Sensing can lead to production of?
virulence factors
AHLs cross the bacterial membranes largely through?
diffusion
AHLs are detected and bound by?
LuxR-type regulatory proteins
When/where does AHLs binding occur?
occurs when the AHL acyl chain enters the hydrophobic acyl-binding pocket
of the LuxR protein
The AHL/LuxR complex then binds to?
a DNA promoter regulatory region and activates the transcription of several Quorum Sensing (QS) genes in the lux operon
Expression of lux-like genes results in a wide range of activities in different bacteria, such as?
light production, virulence, EPS (exopolysaccharide) secretion, motility, and plasmid transfer
Explain Staphylococcus production of ArgD and how it leads to virulence proteins.
(5 steps, very long slide)
1. Basal level transcription of the argABCD operon in Staphylococcus leads to production of ArgD, the preautoinducing peptide (AIP). 2. ArgB trims ArgD into the functional AIP and exports it out of the cell. 3. As the cell population increases, the AIP concentration increases and binds to ArgC, leading to autophosphorylation of ArgC. 4. ArgC-P then activates the transcriptional activator ArgA by transfer of a phosphate group. 5. ArgA-P increases transcription of the argABCD operon as well as activating the transcription of an RNA that leads to the production of virulence proteins
