VL12: HGT of Virulence Factors

Question 1

Why is horizontal gene transfer important?

Answer 1

1. experimental method
2. driving force of evolution
3. medical importance, creation of pathogens and resistant bacteria

Question 2

What is vertical and horizontal evolution?

Answer 2

verical gene transfer: from parents to children

horizontal evolution: uptake of new information, everything else

Question 3

Name 3 general features of gene transfrer in bacteria

Answer 3

• unidirectional- donor to recipient
• donor does not give an entire chomosoem
• gene transfer can occur between species

Question 4

Name 3 mechanisms of HGT

Answer 4

• transformation: gene transfer resulting from the uptake of DNA from a donor
• conjugation: unidirectional genetic transfer between donor and recipient by direct contact
• transduction: gene transfer from a donor ro a recipienr by way of a bacteriophage

Question 5

What factors affect transformation?

Answer 5

• DNA size and state (sensitivity to nucleases)

- competence of recipient (competence factor, induced competence)

Question 6

What happens during transformation?

Answer 6

• DNA gets into the cell

- DNA recombines via recombination (legitimate, homologous or general) with the help of recA and recBC genes

Question 7

What is a bacteriophage made up of?

Answer 7

Head/Capsid
Tail
Contactile sheath
tail fibers
base plate

(nucleic acid and protein for protection and infection)

Question 8

Describe 2 types of bacteriophages

Answer 8

1. Lytic or virulent: Phage that multiply within the host cell, lyse the cell and release progeny phage
2. Lysogenic or temperate phage:Phage that can either multiply via the lyic cycle or enter a quiescenr state in the bacterial cell (lambda)
   - expression of mosr phage genes repressed
   - prophage
   - lysogen

Question 9

Describe how generalized transduction happens

Answer 9

• Generalized transduction transfers any gene
• specialized transduction reansfers specific genes

infection of donor
phage replicarion and degradation of host dna
assembly of phage particles
release of phage
infection of recipient
legitimate recombination

Question 10

What does the F factor do? how is it transferred

Answer 10

F factor (fertility factor): mediates gene transfer

transferred via conjugaton:

• donor F+, recipient F-
• F is self replicating circular dna plasmid
• contains orgin sequence which initiates DNA transfer + genes for hair like cell surface (F-pili/ sex-pili)
• F plasmid nicked at ori, transfer via rolling circle mechanism
• after transfer both cells F+

Question 11

What physiological states can the F Factor be in? and what genes do they transfer when they mate with F-

Answer 11

• autonomous (F+), x F- -> recipient becomes F+, but lwo frequency of donor choromosomal genes
• Integrated F (Hfr) x F- -> recipient rarely becomes Hfr, high transfer of certain donor chromosomal genes
• Autonomous F with donor gene (F’) x F- -> recipient becomes F’, high transfer of donor genes on F’ and low transfer of other donor chromosomal genes

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