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BMR 605 > Test 1 Bacterial Gene Expression > Flashcards

Test 1 Bacterial Gene Expression Flashcards

1
Q

What are the three major mechanisms of Bacterial Gene Transfer?

A

Transformation

Conjugation

Transduction

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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
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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-
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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-
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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
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6
Q

Describe Lysogeny?

A

Genes for some bacterial toxins are transferred to non-toxic strains via lysogeny.

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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)
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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
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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
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10
Q

Define Operator (O):

A

DNA site at which regulatory proteins like repressors bind.

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11
Q

Define Promoter (P):

A

-35, -10 site for RNA polymerase binding, required for accurate, high level initiation of transcription.

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12
Q

What role does the ilvGMEDA operon do?

A

Encodes five genes whose products are required for the biosynthesis of isoleucine and valine.

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13
Q

Transcription of bacterial operons is often polycistronic, meaning?

A

One continuous mRNA spans several structural genes.

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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
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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
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16
Q

Describe the lacZYA operon

A
  • Both positive inducible and negative inducible control
  • Needs both switches to be “ON” position for full expression
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17
Q

What is the role of lacI

A

Repressor

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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
Q

What occurs when the Lac Operon is in a lactose medium?

A
  • 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
Q

Describe diauxic growth?

A
  • 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
Q

Describe Catabolite activation in relation to the lac operon.

A
  • 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
Q

What is the condition of the lac operon in the following environment?

Glucose

A

OFF

29
Q

What is the condition of the lac operon in the following environment?

Glucose + lactose

A

mostly off

30
Q

What is the condition of the lac operon in the following environment?

Lactose

A

ON

31
Q

What is the condition of the lac operon in the following environment?

Other sugars (not glucose or lactose)

A

OFF

32
Q

What is the role of the PTS system in sugar metabolism?

A
  • 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
Q

What is the mechanism of catabolite activation of the lac operon signal transduction pathway under the following condition?

High glucose

A
  • High glcIII (nonphospho)
  • glcIII turns off S1 and S2
  • cAMP levels are low
  • Glucose is used preferentially
34
Q

What is the mechanism of catabolite activation of the lac operon signal transduction pathway under the following condition?

Low glucose

A
  • High P-glcIII
  • Active adenylate cyclase
  • High levels of cAMP
  • lacZYA is transcribed in presence of lactose
35
Q

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

A
  • 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
Q

What is the level of cAMP determined by?

A
  • Adenylate cyclase (converts ATP to cAMP)
    • Activity is determined by P-IIIglc
      • P-IIIglc activates Adenylate cyclase.
  • Phosphodiesterase (coverts cAMP to AMP)
37
Q

What is the detailed mechanism of catabolite activation of the lac operon signal transduction pathway under the following condition?

Low glucose

A
  • 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
Q

Lac Operon Regulation:

Negative inducible?

A
  • lacI + allolactose
    • Lactose sensor
39
Q

Lac operon Regulation:

Positive inducible

A
  • cAMP + CAP
    • ​Glucose sensor
40
Q

Some virulence genes are under the transcriptional control of two-component regulators, what are they?

A
  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
Q

In Bordetella pertussis, a two component system controls expression of a large number of virulence genes, what are these components?

A
  • BvgS (a histidine kinase) phosphorylates BvgA (DNA binding protein) which then activates transcription of toxins (pertussis toxin) and omps.
42
Q

Describe Quorum Sensing:

A
  • 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
Q

Describe Global regulation

A

The regulation of multiple metabolic pathways by a single regulator e.g. cAMP binding protein or quorum sensing.

BMR 605 (10 decks)

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