Lecture 9 Flashcards
T7: podoviridae
-thicc
-naked icosahedral capsid
-60nm
-shirt tail and tail fibers
-lytic no lysogeny
-linear dsdna genome 40kbp
-phage receptor: LPS
true or false: the Ty genome is divided in clusters
true in 3
-class I : early
-class II: dna metabolism
-class III: virion structure and assembly
entry of T7 DNA into cytoplasm
-attached to the surface of the bacterial cell wall
-introduces its phage DNA in bacteria by making a tunnel through the OM, PG and IM
-e.coli rna pol binds to promoter sequence of the phage RNA
-class I genes are expressed
what are the 3 special genes in T7 and what do they do
Gene 0.3: inhibits host type I restriction endonucleases
Gene 0.7: inhibits E coli RNA Pol
Gene 1: T7 RNA Pol
true or false: T7 carries its own polymerase
true
True or false: the DNA ligase in T7 is a class I gene
false: it is a class II gene
what are the 4 class III gene in T7
8: portal protein
9: scaffolding protein
10: capsid protein
11: tail protein
T7 RNA pol
-e.coli rna pol canm only transcribe genes from class I promoters not II and III
-dna entry proceeds until class II promoters are reached
-T7 rna pol encoded in Class I genes
-takes over from e.coli rna pol in transporting DNA into cell
explain t7 dna replication
oop
why do the T7 phage makes concameter
problem:
-dna pol needs a primer to initiate DNA synthesis
-thus the rna primer at the 3’ end of template DNA cannot be removed or replaced with dna=loss in sequence
is T7 dna replication unidirectional or bi
bidirectional
true or false t7 dna replication looks like ecoli DNA synthesis
true
continuous leading and lagging strands
true or falseL t7 encodes all its own DNA replication proteins
true
how are the large concameters of t7 made
formed via 150 bp terminal repeats
t7 phage life replication
ppt 14 lect 9
lambda phage
-siphoviridae
-dsdna
-ssdna at the ends aka cohesive ends
-temperate bacteriophage
-icosahedral dead
-tube like tail non-contractile
-receptor- surgar transport proteins lamB (maltose transporter_
-used to construct the cDNA libraries
what are temperate phages:
able to gropw lytically or exist as a repressed prophage
prophage
integrated phage dna, lytic genes are repressed, passivally replicate with host chromosome
lysogen
bacteria carrying prophage
explain the whole genome of lambda
oop
how does lambda regulate transcriotion
-transcription start: activator and repressor
termination: antiterminator
explain initial transcription events
oop
ppt 20 lec 9 -24
true or false: CII initiates the establishment of lysogenic phage of infection
true
Cll is inactivated by a host cell protease, has a very short half-life (a few minutes), its stability is enhanced by Clll whose expression is driven by PL and can inactivate host cell proteases. Cll itself is much less stable in metabolically
active cells. go see ptt 25 lect 9
go lytic or lysogenic?
-Upon infecting a bacterium, N and Cro are expressed
-Cro suppresses the expression of CI from PRM
-N leads to the expression of early genes CII and CIII
-In metabolic active cells, CII is very unstable, unable to
activate CI expression from PRE, GO LYTIC
-In metabolic inactive cells, CII is more stable, reaches high enough concentration to activate CI expression from PRE, GO LYSOGENIC
retroregulation of int expression
see ppt 27 lec 9
what does the lambda phage need to integrate the DNA and yeet away?
-integrate: INT, IHF
-yeet: int, IHF, Xis
The great escape aka temperate phages-> lytic
-Stresses such as ultraviolet light irradiation causes DNA damage that activates RecA protein which in turn binds
to CI, stimulates the autoprotease activity of CI and leads to CI cleavage.
-Transcription from the PL promoter leads to the production of mRNA that direct the synthesis of both Xis and Int that together with IHF excise and liberate prophage DNA.
cdna
basically you use a replacable region in a phage, you digest it and you digest human DNA and you mix them, now you get a recombinant virion containing genomic DNA
