bacterial gene transfer 6.1 Flashcards
what are 3 methods for bacterial gene trasnfer?
transformation
transduction
conjugation
All three mechanisms require?
Homologous recombination
Homologous recombination takes place when?
closely related DNA sequences with (extensive homology) from two distinct genetic elements are combined into a single element
Recombination is an important ______ process
evolutionary
*cells have specific mechanisms for ensuring that recombination takes place and that it takes place with precision
What is RecA protein?
single-stranded binding protein
- an important enzyme mediator for process of recombination
- Only competent cells are transformable
What is competence?
a state in which cells are able to take up free DNA (must be able to capture and take up DNA on membrane)
competence is related to changes in?
the cell surface that allow binding of DNA
Not all bacteria can accomplish transformation, you MUST have _____ to do so
competence
In the end of transformation, a single strand of transforming DNA is integrated into the chromosome using?
homologous recombination and then a complementary strand is synthesized
Why is the discovery of transformation a seminal event in biology?
it led to experiments demonstrating that DNA is the genetic material of cells (Avery, McLeod and McCarty) and PROVED that DNA was genetic material
What was the experiement for transformation? bacteria used? R-cell and S-cells?
Griffith’s experiment with pneumococcus= Streptococcus pneumoniae using S cells (smooth colony cells with capsule= virulence factor) and R cells ( rough colony cells without (incapable of making) capsule)
DId S cells or R cells kill the rats?
heat killed S cells= alive
Live S cells= dead
Live R cells= alive
Live R cells + heat killed S cells= dead
the key to Streptococcus pneumoniae being deadly is? also proved?
the capsule
- bc heat killed S cells with capsule didn’t kill rat BUT heat killed S + live R AND live S cells alone did kill rat
- ***DNA as genetic material
What prevents bacterial uptake by macrophages?
capsular polysaccharide
What is transduction?
1) transferred DNA is carried in the capsid (protein coat) of a bacteriophage.
2) The donor’s DNA replaces part or all of the viral genome in the bacteriophage core.
* Therefore the virus is now defective, bc it doesn’t have all of the genetic information for its own replication
Transduction involves the transfer of?
host genes from one bacterium to a bacterial virus and then from the virus to another bacterium
In generalized transduction random fragments of the DNA from the bacterial
chromosome are incorporated into?
the virus particle
Efficiency of this type of transduction is low?
generalized transduction
specialized transduction requires?
- -1)viral DNA to be incorporated into the host chromosome of the donor
- -2)viral DNA to then be excised from the donor host chromosome.
- -3)imprecise viral DNA excision from the host chromosome so that adjacent host genes are also excised (this virus may not be defective).
- –4)viral infection into another bacterium (recipient); transducing efficiency in this case may be very high
What type of transduction may NOT have defective viruses after DNA is extracted?
specialized transduction
Efficiency of this type of transduction is high?
specialized transduction
Temperate virus
a virus whose genome is able to replicate along with that of its host and not cause cell death. This is called a state of lysogeny
Provirus (Prophage)
the genome of a temperate virus when it is replicating within the host chromosome
Lysogen
a bacterium that contains a prophage
Lysogenic pathway
a series of steps after virus infection leading to replication of viral genome as a prophage
Lytic pathway
series of steps after virus infection that leads to virus replication and destruction of the host cell
Some temperate phages cause
phenotypic changes in the bacteria they infect even without transducing bacterial genes
What does state of lysogeny mean?
a virus being able to replicate its genome (as well as its host) and NOT cause cell death
lambda phage is a type of?
temperate phage
In the case of temperate phages such as lambda phage, the virus genome gets incorporated into the?
bacterial DNA at the same spot each time
temperate phage have what type of transduction?
specialized transduction
-only a few of the same bacterial genes are transduced each time with RARE mistakes
In the normal lytic event the excision of phage DNA from the host DNA leads to?
normal phage production without host DNA excision
In the lysogenic state, viral genes
confer new?
properties on the cell
phage conversion are examples of _____ state
lysogenic state
Give 2 examples of phage conversion?
1)toxin production by pathogenic bacteria
such as Corynebacterium diphtheriae
2) surface polysaccharide structure in
Salmonella anatum
