Genetic Variation, Gene Transfer and the Evolution of Virulence Flashcards Preview

Disease & Defense - Unit 2 > Genetic Variation, Gene Transfer and the Evolution of Virulence > Flashcards

Flashcards in Genetic Variation, Gene Transfer and the Evolution of Virulence Deck (21)
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1
Q

Tyeps of bacterial regulation of gene expression (2)

A
  1. regulation of transcription

2. regulation of transcription via DNA rearrangement

2
Q

Bacterial regulation of transcription & virulence

A
  • control gene expression based on environmental conditions

- e.g. up-regulation of virulence genes in low-iron conditions as occurs in human/animal host

3
Q

Bacterial DNA rearrangement & virulence

A
  • “phase variation”
  • e.g. salmonella typhimurium: invertible segment of DNA reversibly switches synthesis between two flagellar antigens
  • e.g. N. gonorrhoeae: alternation between different antigenic forms of pili
4
Q

Mechanisms of bacterial genetic variation (3)

A
  • spontaneous mutation
  • recombination
  • acquisition of new genes
5
Q

Bacterial spontaneous mutation and virulence

A
  • randomly occurring gene alterations
  • low mutation rates
  • examples: 1. Pseudomonas/TB antibiotic resistance 2. Strep. pyogenes increased invasiveness due to single amino acid change @ pyogenic exotoxin B
6
Q

Bacterial recombination and virulence

A
  • site-specific or homologous recombination –> new strains with new properties
  • e.g. N. gonorrhoeae
  • possibility of new traits/virulence factors
7
Q

Types of bacterial acquisition of new DNA

A
  1. acquisition of transposable elements
  2. bacteriophage conversion
  3. acquisition of plasmid
  4. acquisition of “pathogenicity islands”
8
Q

Transposon definition + types

A
  • discrete segment of DNA capable of moving itself from one chromosomal location to another
  • “insertion sequence”=encdoe transposase
  • “complex transposons”=carry additional genes such as those encoding antibiotic resistance, toxins, virulence factors, etc.
9
Q

Bacterial plasmids definition

A

autonomously replicating, usually circular, extrachromosomal DNA; may be transferred between bacteria via conjugation or transduction

10
Q

“Pathogenicity islands” definition

A

large segments of DNA in some bacterial strains that encode virulence factors.

11
Q

Types of bacterial gene transfer

A
  1. Transformation
  2. Transduction
  3. Bacterial conjugation
12
Q

Bacterial transformation process

A
  1. naked DNA in vicinity
  2. transformable species becomes competent for DNA uptake @ certain point in growth cycle –> take up naked DNA
    3.
13
Q

Bacterial transduction definition

A

DNA transfer mediated by bacteriophage

14
Q

Growth process of a “virulent” bacteriophage

A
  1. virus attaches and injects genome into bacteria
  2. viral genome replicated and proteins produced (“latent period”
  3. viral proteins assembled and released upon lysis of cell
15
Q

Characteristics of “temperate” bacteriophages

A
  • don’t invariably kill host cell
  • lytic response: phage multiplication and cell lysis OR
  • lysogenic response: host cell remains viable and viral DNA maintained w/in a prophage state
16
Q

Prophage state characteristics

A
  • viral DNA inserted into host cell genome
  • viral DNA replicated as part of bacterial chromosome
  • repressor protein maintains prophage state, usually until stress conditions –> stimulated to enter lytic state
17
Q

Mechanisms of transduction

A
  1. error in DNA packaging results in incorporation of host bacterial DNA into new bacteriophage –> injected into a new bacteria to produce genetic recombinant (“transductant”)
  2. bacterial plasmid is incorporated and transduced
  3. bacteriophage conversion: bacteriophage genome encodes genes expressed during lysogenic state that cause new trait in bacteria
18
Q

Bacterial conjugation definition

A

genetic transfer via physical contact between recipient and donor cells; usually mediated by plasmids

19
Q

Conjugative plasmids definition

A

self-transmissible; mediate own transfer

20
Q

F plasmid paradigm

A
  • self-transmissible plasmid discovered in E.coli
  • contains info for: 1. autonomous replication 2. sex pili 3. conjugative transfer 4. ability to integrate into bacterial chromosome
  • transfer initiated by round of DNA synthesis begining at oriT (origin of transfer)
  • transferred via conjugation bridge
21
Q

Process of chromosome transfer by Hfr strains

A
  1. certain F+ cells may transfer sections of chromosomal DNA = “Hfr mating type”
  2. sex factor is linearly inserted into bacterial chromosome (instead of extrachromosomal)
  3. transfer is unidirectional w/polarity