Transduction Flashcards
summarize generalized transduction
1) phage infects cell
2) host DNA hydrolyzed, phage proteins/DNA replicated
3) during packaging, error occurs where host DNA is packaged
3) when affected phage infects another cell, crossing over may occur to form recombinant bacteria
summarize specialized transduction
bacteria already has prophage, imprecise excision during induction causes phage to have some bacterial DNA with phage DNA
- injection of that combination can cause some extent of recombination
what are recombinants/transductants
outcome of when in subsequent infections, Host DNA is injected in and recombines with new bacterial DNA
whats a transducing particle
phage with capsid head containing host DNA
what are 3 features of generalized transducing phages
1) non specific pac sites
2) headful packaging mechanism
3) broad host range
what are pac sites
non specific pac sites are sites recognized by enzymes for cleaving
what is headful packaging in generalized transducing phages
mechanism that packs DNA into capsid head. has no specific regulations that stop it from packing bacterial host DNA.
- once mechanism is initiated, concatemer with host DNA and phage DNA is cut at unit lengths and packaged
what is broad host range in reference to transducing phages
means that phages with bacterial DNA can inject into any cell without restriction or specificity
what is two factor cross
when genes are close to each other on genome they would be co-transduced (where 2 genes are injected into recipient and undergo recombination)
how do you calculate co-transduction frequency
(# of cotrasnductants/ total transductants) X 100%
explain specialized transduction in refence to lambda-D-gal
lamda phage is integrated in host DNA and is excised improperly.
excision of gal+ leads it to prevent capsid head formation
excision of bio+ leads a loss of ability to integrate phage DNA into host–> makes it lytic
what are characteristics of specialized transducing phages (lamda-D-gal)
1) once integrated, phage requires helper phage (to produce head/tail or proteins for lysogenic mechs)
2) can create di lysogens
what are di lysogens
lysogenic phage (so one integrated in host genome) with 1 phage dna being wild type (donates its properties to) tranducing phage (one thats missing functions)
this whole process is high frequency transduction (HFT)
what is lysogenic conversion
promotor genes called morons in which toxin phage is able to integrate itself into them and make non toxic bacteria’s toxic
explain lysogenic conversion in enterohemorrhagic E-coli
SOS response induced in host leads to inactivation of STX phage (represses lytic genes– so now not repressed)
- elevates expression of stxAB genes (toxic)
- expression lyses and releases shiga toxins which leads to
HAMBURGA DISEASE (HUS)
