Bacteriophage and their lifecycles Flashcards
Bacteriophage anatomy
-Head caspid proteins that contain genetic material inside
-neck and collar
-tail core
-tail sheath
-base plate
-tail fiber (only found in T4, not lambda)
Lytic cycle
-bacteriophage attach to the host cell (adsorption) by identifying protein on the membrane
-inject of DNA into the host which then circularize
-contain gene which commander the host transcriptional and translational machinery to produce phage component
- after enough phage has been prodce, create a protein that break the cell membrane/wall. release the phage into the enviroment
Lysogenic pathway
-bacteriophage attach to the host cell (adsorption) by identifying protein on the membrane
-inject of DNA into the host
-c1 gene in the phage bind to a specific region in the phage DNA (block lytic pathway)
-also active int (intergrase)which lead to recombinant event
-combine attP in the phage attB in the bacteria
-integrate into the host DNA
-this slow down bacteria division and can revert back to lytic pathway
lysogens
-bacteria that has integrated phage DNA into its DNA
lysogen and superinfection
-lysogen is immune to infect more lambda
-the intergrated phage DNA still produce c1, prevent activation of newly inserted phage DNA
stress and prophage induction
-under stress, e.coli produce new protease which degrade protein
-c1 is sensitive to the protease, which can no longer block lytic pathway
-this lead lytic cycle being activate by induction of prophage
what is transduction
◆Transduction uses phage to act as a vector carrying genes from the donor bacterium to the recipient
◆The small genome size of phage means that they can only carry a small portion of the whole bacterial chromosome.
◆Closely linked genes can be separated or mapped by transduction
two type of transduction
●Generalised transduction can be used to map genes anywhere on the bacterial chromosome
●Specialised transduction is limited to certain regions of the bacterial chromosome
Generalised Transduction pf P1
●Most commonly used E.coliphage
●Genome size of ~100kb (~2% of E.coli)
●At low frequency host chromosomal DNA instead of phage DNA is packaged.
●Resultant particles are infectious but can not make progeny phage
●A variant of P1 known as P1kc has lost the ability to recognise its own DNA and packages host DNA at a higher efficiency than the wild type.
phage P1 mutated effect
●Infection by a phage particle which has packaged host DNA will produce a partial diploid E. colicell.
●This cell will not make more phage particles as there is no phage DNA, so the infection is not lytic.
●Inserted DNA can not circularise and is therefore unstable
●Homologous recombination between this DNA and the bacterial chromosome can occur to produce recombinants (transductants)
●A double recombination event is required (because bacterial dna is not linear)
generalise tranduction trend
◆The closer that genes are together then the more likely they are to be within the same phage head
◆The closer that genes are together then the less likely that a cross over occurs between them
◆The frequency of cotransduction measures both of these parameters
How does specialise trandcution work
-occur in the lisogenic pathway, when it revert back into the lytic pathway, the phage dna exit from the host dna
-error can occur and some of the host dna is excised along phage dna
-due to maximum pakage size of 55kb and actual genome size of 48kb, some phage dna are left behind
-can only take gene adjacent to the attachment site
what can specialise transduction do
-use the helper phage to in a coinfection exp, the phage can insert its dna into a new host
-lead to duplication of some gene (patrial diploid)
-complimentary test can be perfom
-recombination of the gal region can occur but would not represent a complimentary test (can be avoided by using a defective phage)
