Test 1 Bacterial Gene Expression Flashcards
1
Q
What are the three major mechanisms of Bacterial Gene Transfer?
A
Transformation
Conjugation
Transduction
2
Q
Describe Transformation?
A
- Direct uptake DNA from surrounding environment
- Allows for evolution of DNA over time
- Useful technique in micro lab
- Introduces genes to bacteria
3
Q
Describe Conjugation?
A
- Transfer of DNA from a bacterial cell of one mating type (donor) to cell of the other mating type (recipient)
- F-Pilus mediates cell to cell contact.
- Cells carrying the plasmid are designated F+
- Recipients of the DNA lack F factor and are thus F-
4
Q
How is donor mating type determined?
A
- By the presence of a type of transmissible plasmid called the F Factor (or F plasmid)
- Recipients of DNA are F-
5
Q
Describe Transduction?
A
- Transfer of DNA via bacteriophage
- Virus picks up DNA, transfers to another bacteria
- Lytic vs Lysogenic phages
- Generalized vs specialized transduction
- Phages that replicate only via lytic cycle: virulent
- Phages that does both lysis and incorporate host DNA: temperate
6
Q
Describe Lysogeny?
A
Genes for some bacterial toxins are transferred to non-toxic strains via lysogeny.
7
Q
Describe Transposition?
A
- Transposons are DNA segments within bacterial DNA.
- Can be excised and re-integrated in new location in DNA
- Once excised, can also be moved to plasmid
- Mechanism of action:
- Bacteria #1 is resistant
- Transposon carries resistance to a gene
- Transposon moved to plasmid which then transfer to other bacteria (VRE)
8
Q
Regulation of Gene Expression
A
- Regulatory Elements in prokaryotic genes
- Control of Transcription Initiation
- Control by Two Component Regulators
- Quorum Sensing
- Global Regulation
9
Q
At what levels can the abundance of a protein be controlled in prokaryotic cells?
A
- Gene copy number
- Transcription initiation (lac and trp operons)
- mRNA stability
- Tranlation initiation (Shine Dalgarno)
- Protein Stability
10
Q
Define Operator (O):
A
DNA site at which regulatory proteins like repressors bind.
11
Q
Define Promoter (P):
A
-35, -10 site for RNA polymerase binding, required for accurate, high level initiation of transcription.
12
Q
What role does the ilvGMEDA operon do?
A
Encodes five genes whose products are required for the biosynthesis of isoleucine and valine.
13
Q
Transcription of bacterial operons is often polycistronic, meaning?
A
One continuous mRNA spans several structural genes.
14
Q
Negative control always requires a ? and what are the two types?
A
- Repressor
- Two types:
- Negative Inducible: Ligand inactivates repressor
- Negative repressible: Ligand activates repressor
15
Q
Positive control always involves an ? protein, and what are the two subtypes.
A
- Activator
- Two types:
- Positive inducible: Ligand activates activator
- Postive repressible: Ligand inactivates activator protein
16
Q
Describe the lacZYA operon
A
- Both positive inducible and negative inducible control
- Needs both switches to be “ON” position for full expression
17
Q
What is the role of lacI
A
Repressor
18
Q
What is the role of lacP
A
Promoter
19
Q
What is the role of lacO
A
Operator, and binding site for lacI
20
Q
What is the role of lacZ?
A
- Encodes B-galactosidase which cleaves lactose into glucose and galactose; also can convert lactose to allolactose, the true inducer.
21
Q
What is the role of lacY?
A
Encodes a permease which facilitates the uptake of lactose into the cell.
22
Q
What is the role of lacA?
A
Encodes transacetylase which may detoxify lactose metabolites.
23
Q
In a glucose medium lac repressor binds to?
A
lacO
24
Q
What is the result when the repressor binds to lacO?
A
- The bound repressor overlaps lacP and physically blocks the progression of RNA polymerase.
- No transcription of lacZYA
25
What occurs when the Lac Operon is in a lactose medium?
* Initially low level of **lacZ** gene product converts lactose to allolactose which causes a conformational change.
* This results in the repressor no longer being able to bind to the operator.
* **lacZYA** can now be transcribed and translated at high levels.
* **Dependent on high levels of cAMP.**
26
Describe diauxic growth?
* Given the preferential metabolization of glucose, all glucose is consumed before lactose metabolism is initiated. This results in a **sequential use** of nutrients and a corresponding lagging growth period as glucose becomes scarce before lactose use begins.
27
Describe **Catabolite activation** in relation to the **lac** operon.
* **Positive control**
* Required in order to turn off lacZYA transcription when glucose is present in the growth medium.
* Relies on cAMP binding protein
* cAMP levels are determined by glucose levels.
28
What is the condition of the lac operon in the following environment?
Glucose
**OFF**
29
What is the condition of the lac operon in the following environment?
Glucose + lactose
**mostly off**
30
What is the condition of the lac operon in the following environment?
Lactose
**ON**
31
What is the condition of the lac operon in the following environment?
Other sugars (**not glucose or lactose**)
**OFF**
32
What is the role of the PTS system in sugar metabolism?
* PTS components transport sugars like glucose and mannose across the inner membrane.
* When glucose is low:
* P-IIIglc activates adenylate cyclase which produces cAMP.
* This turns off nonPTS sugar transport systems like lac permease and maltose binding protein.
33
What is the mechanism of catabolite activation of the **lac operon** signal transduction pathway under the following condition?
High glucose
* **High glcIII (nonphospho)**
* **glcIII turns off S1 and S2**
* **cAMP levels are low**
* **Glucose is used preferentially**
34
What is the mechanism of catabolite activation of the lac operon signal transduction pathway under the following condition?
## Footnote
**Low glucose**
* **High P-glcIII**
* **Active adenylate cyclase**
* **High levels of cAMP**
* **lacZYA is transcribed in presence of lactose**
35
What is the mechanism of catabolite activation of the lac operon signal transduction pathway under the following condition? Specifically in reference to cAMP
High glucose levels
* Levels of cAMP are very low and **IIIglc is relatively high.**
* low cAMP means cAMP-CAP complex is not present
* **Transcription of the lac operon is off**
36
What is the level of cAMP determined by?
* Adenylate cyclase (converts ATP to cAMP)
* Activity is determined by P-IIIglc
* P-IIIglc activates Adenylate cyclase.
* Phosphodiesterase (coverts cAMP to AMP)
37
What is the _detailed_ mechanism of catabolite activation of the lac operon signal transduction pathway under the following condition?
Low glucose
* Low glucose levels mean P-IIIglc level is high
* **Adenylate cyclase is activated and therefore cAMP levels are high.**
* cAMP binds to catabolite activator protein (CAP)
* cAMP-CAP complex binds to site in **lacP**
* This results in **helix unwinding** at downstream sites and **facilitates the binding** of RNA polymerase and therefore increases the transcription of the operon.
38
Lac Operon Regulation:
Negative inducible?
* **lacI + allolactose**
* Lactose sensor
39
Lac operon Regulation:
Positive inducible
* **cAMP + CAP**
* ****Glucose sensor
40
Some virulence genes are under the transcriptional control of two-component regulators, what are they?
1. 1st protein component: Membrane sensor that detects environmental signals.
* Signals include oxygen and osmolarity
* Sensor can be a protein kinase.
2. Transcriptional activator (e.g. CRP) or in some cases a repressor.
* Termed response regulator.
41
In Bordetella pertussis, a two component system controls expression of a large number of virulence genes, what are these components?
* BvgS (a histidine kinase) phosphorylates BvgA (DNA binding protein) which then activates transcription of toxins (pertussis toxin) and omps.
42
Describe **Quorum Sensing**:
* Set of genes that are activated when bacteria cell concentration reaches a threshold.
* Bacteria produce a signaling molecule (S) which bind to cell wall receptors and transduce a signal to activate gene expression.
* This is used by some bacteria to produce biofilms.
43
Describe **Global regulation**
The regulation of multiple metabolic pathways by a single regulator e.g. cAMP binding protein or quorum sensing.
