Phage and Genetic Exchange Flashcards
bacteriophage
viruses that infect bacteria
what genetic material can a bateriophage has
RNA and DNA
how do bacteriophage invade bacteria
tail fiber attach to surface
DNA is injected into the cell
how does filamentous phage invade bacteria
ingested by bacterium as a whole
what determines hosts specificity of bacteraphage
tail fiber proteins and host receptors
what happens to a phage after it has infected a bactrium
enters lytic or lysogenic life cycle
what happens in lytic cycle
phage replicates it DNA
lyses bacteria
name 2 processes that occur in lysogenic cycle
prophage
phage induction
prophage
DNA is integrated into bacterial chromosome or plasmid
phage induction
prophage an excise itself from the host DNA and start lytic cycle to multiply and release from bacteria.
name three types of bacteriaphages
virulent
temperate
filamentous
virulent bacteraphage does not have what
lysogenic cycle
temperate bacteraphage have what
either lytic or lysogenic cycle
filamentous phages do what to bacteria
no lyse of bacteria
continuously secrete new phages
what are 2 events in the lytic cycle
phage DNA replication
packaging
replicative form in lytic cycle
double stranded circular DNA
pac site in lytic cycle
phage coat proteins bind to specific DNA sequence
-packs DNA into an intact new phage
lambda phage replication replicates what
lambda phage genome that is linear dsDNA
cos sites
cohesive ends of lambda phage genome
what happens when lambda is injected into cell
cos site join to form circle
what types of replications are seen in lambda phage
0 replication
rolling circle replication
for lambda genome what is cancatermers? what process makes it?
tandem repeats
rolling circle replicatoin
for linear dsDNA, characteristic of ends that isn’t lamdba phage
blunt end without sticky cos sites
for linear dsDNA, what is stage 1
replication of multiple origins
for linear dsDNA, what is stage 2
replication following recombination
how are cancatermers formed in linear dsDNA,
recombination at ends of daughter DNA
what type of packaging does linear dsDNA have
headfull packaging
what is headfull packagin
phage head is filled with DNA until it is full
phages using headful packaging are more likely to
pack host bacterial chromosome DNA for genetic exchange
lysogen
bacterium that harbors a prophage
for temperate phage, what determines whether it goes into lytic cycle or lysogenic cycle
balance between CII synthesis (lysogeny) and gene products for DNA (lytic cycle)
what are 3 genes important for the lysogenic swtich
CI, CII, CIII
what is the CI gene
“master switch” of lysogeny
in early infection of bacteria what genes get infected
both CII and CIII
what does CII do
activates expression of CI
What does CIII do
prevent degradation of II
what 2 domains does CI contiain
dimerization domain
DNA binding domain
what are 2 functions of CI
transcriptional repressor for lytic cycle
transcription activator- its own expression
how does phage DNA integrate into the host chromosome
site specific DNA recombination b/w phage attachment site (attP) and bacterial attachment site (attB)
the recombination between phage attachment site (attP) and bacterial attachment site (attB) is mediated by who
phage integase
lysogeny (lysogenic cylce) is maintained by what
CI dimmers
When DNA gets damaged with phage inside DNA what happens
- ssDNA produced
- ssDNA binds RecA
- -then RecA binds CI
- CI leaves DNA
When CI autocleaves form DNA what genes are de-represse
cro
integrase
excisase
what does cro gene do
inihibit further expression of CI
integrase and excisase form what
site-specific recombinase complex
recombinase complex does what
recognizes hybrid attachment sites and excises the prophage from host chromosome by site specific recombination
-DNA becomes ciruclar
what is genetic exchange
genetic exchange between 2 bacterial cells
name 3 mechanisms for genetic exchange
transduction
conjugation
transformation
define transduction
transferring DNA from a donor cell to a recipient cell by bacteriophage
what are two types of tansduction
generalized
speacilized
what makes a phage a transducing phage
- package host DNA
2. low sequence or no sequence specificity requirement for packing DNA into head
What is generalized transduction
phage infect bacterium
host DNA fragmented
phage DNA made with 1% host DNA fragment in it
Specialized transduction
induction of prophage from lysogency
- takes places b/w host and bacterial DNA
- new phage have piece of host DNA
- usually host DNA that is close to attachment site gets mixed in
conjugation
transfer of DNA from a donor cell to a recipient cell by plasmid
conjugation requires what
cell-cell contact initiated by sex/F pilus
what is a plasmid
circular dsDNA exists in bacterium independent of chromosome
self-transmisssible plasmids also called what? and characterstic
F factor/plasmid
have all the genes needed for moving among cells
mobolize plasmids
have some but not all the genes for transmission, need F plasmid for help
what is sex/F pilus
bacteria containing an F plasmid have a hair life appendage on their surface
what does F pilus initiate
cell-cell contact b/w donor and recipient cells during conjugation
F + bacteria or male bacteria
bacteria with an F plasmid
donors of DNA conjugation
F- bacteria
no sex pilus
recipients during conjugation
steps for DNA transfer during conjugation
- nick DNA by endonucleuase
- unwind helicase and transfer
- synthesis of DNA in new strand
Steps for cell connection for conjugation
mating bridge
what initiates the transfer of DNA in conjugation
a cut at OriT - origin of transfer on plasmid
in conjugation , in what direction is DNA transferred
5’ to 3’
tranconjugate
the call that has received a transferred F plasmid in conjugation
what is high-frequency recombinant strains or Hfr
integrated with chromosome F plasmid
Where does F plasmid exist as an episome
outside the chromosome
why does a Hfr strain cause high frequency of recombinant strain?
- chromosome DNA of Hfr bacteria can be trasnferred to recipient strain
- integrated F plasmid can be released from chromosoe and take some chromosome DNA with it
how is Hfr stain trasnfere
- transfer unidirectional from 5’ to 3’
2. genes closer to oriT transfer first
what does R plasmid carry
multiple antibiotic resistance genes
how does R plasmid acquire antibiotic genes
transposon-mediated recombination
MRSA (methicillin resistant S. aurea) , scary!
resistant to virtually at bacteria
vancomycin- only one not resistant
is vancomycin resistance common
yes
Transformation
uptake of naked DNA by bacterial cell
tranfection
Eukaryotic cells take up of naked DNA
competence
ability of bacteria to take up naked DNA
competence pheromes
signal cells to become competent
