Bacteriophage Flashcards
what is a bacteriophage
viruses that infect bacteria
what does a phage particle generally consist of
a genome (ssDNA or dsDNA) contained within a protein capsid
what is a virus
a noncellular particle that infects a host cell and directs it to produce progeny particles
why does the replication of phage require host cell machinery
energy production and nutrient aquisition, particle building blocks (nucleotides and amino acids), protein synthesis
what is the lytic phage replication cycle
- bacteriophage attaches to host cell 2. phage inserts its DNA (genome) 3. phage genome circularizes 4. cell synthesizes capsid proteins 5. host DNA is degraded and cell replicates phage genome 6. phage DNA is packaged into capsids 7. host cell is lysed to release phage progeny
how do bacteriophage perform step one of the lytic cycle (attach to the bacterium) / is this attachment specific / how does specificity possibly differ
the tail fibers on the phage have tips that contain proteins that bind to important bacterial surface molecules / yes this attachment is specific / could be species specific or strain within a species specific
what is a capsular polysaccharide / how do phage get around it
it defends the cell against phage infection as a physical barrier / they have enzymes on the tip of their tail fiber that chews through the polysaccharide and binds to the LPS
how does the viral DNA enter the bacterium / what does the tail fiber do for insertion of DNA
when the phage attaches it triggers a structural rearrangement of phage tail sheath (contracts) / it penetrates the host cell envelope that releases the phage genome
what drives the translocation of the DNA into the host cell
the pressure within the capsid
what are the early genes expressed in phage reproduction
DNAse and DNA replication machinery
what does the early DNAse do
degrades the host genomic DNA which opens up important nucleotides
when is the DNA replication machinery produced
when the DNA is circularized
what are the late genes produced in replication and particle assembly of phage
capsid proteins, DNA packaging machine, holins and lysins
what do the capsid proteins do / what does the DNA packaging machine do
they self-assemble to form empty particles / loads the phage particle with replicated genome (uses ATP)
how do bacterial cells detect the phage DNA from their own
they methylate their DNA so nucleases know what to selectively degrade
what do holins do for cell lysis / what do lysins do for cell lysis
they create a hole in the membrane of the cell / they chew up peptidoglycan which explodes the cell
what is the difference between a lytic phage and a temperate phage
temperate phages integrate themselves into the host genome once the phage DNA is injected
how do temperate phages integrate their DNA into a host / what happens to the phage once integrated
the integrase recognizes a specific attachment site on the host chromosome and integrates into that specific locus / it goes dormant
what is the integrated phage called / when does a temperate phage come out of its bacterial cell
a prophage / it stays in the host genome and is vertically transmitted to the progeny until environmental signals trigger the lytic cell conversion (reenters the lytic phage replication)
what is transduction / how does it happen
the process in which bacteriophages carry host DNA from one cell to another / occurs accidentally as a result of the phage life cycle
what are the two type of transduction
Generalized transduction and Specialized transduction
what is generalized transduction /which phages can do this / how does it happen
when part of the undegraded host DNA gets packaged into the capsid / both lytic and temperate phages can do this / host DNA does not fully degrade
what is a phage containing host DNA called / are these particles specific to what DNA they can hold / can a transducing particle cause infection
a transducing particle / no it can be any piece of the host DNA / no they cannot but they can cause a change in the genotype of the recipient cell
what is specialized transduction / which cells can do it
when a temperate phage re-enters the lytic cycle and does not re-circularize correctly taking some host chromosome with it / only lysogenic temperate phages because it requires lytic reactivation
what is the result of infection of a new host with a specialized transducing particle / what can this lead to
gene transfer from the previous host to the new host / can lead to infection or can cause change in the genotype of the recipient
what is the major driver of bacterial and eukaryotic evolution
bacteriophage evolution
what is the analogous system in both bacteria and eukarya
the STING protein that turns on antiviral within cells does the same thing in bacteria but causes the degradation of all NAD (kills the cell)
can bacteriophage be used to fight infection in eukarya
yes
