MT3 Session 13: Bacteriophages Flashcards
T-even bacteriphage parts
type of DNA/RNA
capsid, tail=sheath+tube, 2 sets of 6 tail fibers, baseplate
linear dsDNA
T-even bacteriophage attachment
to LPS, porin OmpC
entry mech of T4
tail fiber bind, baseplate binding induces sheath contraction, cell wall degrade, pressure pushes DNA in
virus life cycle necessities
- attach to host cell - use host receptor
- genome entry
- virion assembly
- exit
burst size
#virus/ particle that burst =#virus after 1st rep/#virus originally
“early genes”
for DNA rep, regulate/lack of
“late genes”
for lysis
mech that temperate phages use to incorporate into host DNA
site specific recombo
name of phages that:
undergo lytic cycle
undergo lytic AND lysogenic
virulent, temperate
early gene fxns of T4 include
cleave host DNA, replace key host enzymes
replication method of T4 - mech list
rolling circle :
- linear circularizes
- nick
- detach + replace
- fll and cut
Lytic cycle steps
- attachment and inject
- early genes transcribed
- rolling circle rep
- late genes make head and tail
- package heads
- add tail
- add tail fibers
- pop!
late genes of T4 include
making capsid, tail
eclipse period
after adding cells, when [virus]=0, before rep
latent period
eclpse period + replication, haven’tpopped
rise period
when lysis releases until constant concentration of viruses - ALL FREED
lysate
end pt suspension of particles proportional to burst size x cell density : (#v )(#cells) \_\_\_\_\_\_\_\_\_\_\_\_ (cell)(vial)
plaque assay steps
add phage to bacteria, to agar
pour on plate -> see plaque
how do you find out the sequential steps of viral assembly?
use defectives with conditional lethal mutation:
abnormal features, stopped progress
temp sensitive, nonsense mutations+nonsense supressor tRNA
T4 mutant gne 19
won’t create internal tube onto baseplate
so see only baseplates
concatemer
long DNA line - repeat a chromosomal unit mult times
terminal redundancy of T4
has 3% more of normal chromosome length - @ beginning repeated at end
bacteriophage λ
morphology
icosa head, tail, no tail fiber
bacteriophage λ
receptor
LamB = maltoporin - for maltodextrin (starch degrade prod - xglucose lines
how do you get more bacteriophage λ’s to infect a single cell?
add maltose
cells will make more maltoporins –> more entry sites
what does T4 infect?
E coli
what does bacteriophage λ infect?
E coli
what does bacteriophage P22 infect??
S. enterica
lysogen
resultant host in lysogeny after viral dna is incorporated
name of phage in quiescent state
prophage
bacteriophage λ: virulent? temperate?
temperate
lysogeny
incorporation into hst DNA
name of cause for prophage exiting the host DNA
induction
lysogeny rep:
theta replication - bidirectional + site spec recombo
gene regulation for lysis/lysogeny
both have ___
both have early genes at some point
lysis: early off, late on
lysogeny: lysis off (early, late), integration on
bacteriophage λ late genes
REGULATION
N (early) allows Q(late): there’s a cascade before committing
temporal so all steps are completed in order before proceeding
bacteriophage λ encapsulation mechanism
still has concatemeric DNA
TERMINASE cuts dna at COS (cohesive site) site with sticky ends for RECIRCULARIZING
bacteriophage λ LYSOGENY INTEGRATION
protein
mech
- RECOMBINASE to recog host sites &no RecA
site specific recombo:
-chromosome attW.w split in half, λ attXx site cut in half by INTEGRASE –> forms Wx, wX - need EXISIONASE to cut it back out because the attachment sites are no longer the same
attP, attB, att_
attachment site in bacteriophage λ for site specific recombo
why do you need exisionase in bacteriophage λ?
site specific recombo creates two recominant attachment sites, so integrase can’t catalize the back reaction because it can’t bind
bacteriophage λ repression
c1
bacteriophage λ derepression
RecA starts induction of prophage: causes cleaves LexA ,
LexA
represses synthesis of DNA -supresses SOS system
why is RecA a good induction starter for bacteriophage λ?
it cuts out the prophage when it detects DNA damage
-> indicates host is compromised–>
aberrant recombination
improper excision allows bacteriophage genes to be left in host, and phage carries host genes (likeshiga toxin)
how does Phave P22 encapsulate?
cuts when head is filled up “headful encapsulation”
what phage often does generalized transduction (swaps its carrier DNA for the host’s)
P22
M13 life cycle
slow release- don’t lyse host cell
- insert circular ssDNA -> dsDNA
- replicate circular ssDNA, assemble
- have phages bud out as the cell grows (at slower rate)
colored bacteriophage plaques o f M13
b galactosidase or not (white)
