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GENE TRANSFER MEDIATED VIRUSES (Temperate infection (:angel: by Lysogenic…
GENE TRANSFER MEDIATED VIRUSES
Bacteriophage
Viruses that
infect bacteria
:pencil2: 10-400nm diameter
2 types
:smiling_imp: Virulent :arrow_right:
multiplies and lyses
host cell
:angel: Temperate :arrow_right: either :smiling_imp: OR
remain in host
without destroying it
:check:
T4 phage
example of
virulent infection
:smiling_imp:
infect
E.coli
:pencil2:DNA~165kb long contained in
Capsid head
Tail
is used for
host attachment
Lytic cycle
:recycle:
:one: Virus attaches to host
receptor
:two: Viral DNA injects into host :no_entry:
capsid remains outside
:three:
Synthesis
:arrow_right: host machinery redirected to
make phage components
:arrow_right:
host's DNA degraded
:skull_and_crossbones:
:four:
Assembly
:arrow_right: Baseplate, head and tail assembled separately :arrow_right:
packasome
protein
fill capsid with viral DNA
:five:
Lysis
:arrow_right:
holin
crates holes in
E.coli
:arrow_right:
lysosomes attacks peptidoglycan
Transduction
Tested by Lederberg and Zinder
Recombination of viral DNA
crossover occur :arrow_right: refers to break and rejoin DNA
able to use
recombination frequency
to estimate the distance between bacteria and phage genome
Phage crosses
:couplekiss:
Tested by infecting
E.coli
by T4 phages with two different opposite traits
Generalized transduction
:star:phage can carry any part of bacterial chromosome :arrow_right:
random DNA fragments are mistakenly packaged into virus :arrow_right: infects to other bacterium
occurs during lytic cycle
:smiling_imp:
Specialized Transduction
:star:an error in the
lysogenic cycle
of temperate phage :arrow_right: cause the
improper excision
of prophage :arrow_right: uneven excision :arrow_right: phage only carries the bacterial DNA
near phage insertion site
to infect other bacterium
Temperate infection
:smiling_imp: by
Lytic cycle
:recycle:
:angel: by
Lysogenic cycle
:recycle:
:one: Phage injects its DNA into host cell
:two: Phage DNA integrates into host chromosome
:three: Prophage DNA is copied when cell division occurs
:four: exposure to stress (
UV light
) triggers the excision of viral DNA from host chromosome :arrow_right: :one:
:warning: Viral DNA remains into host :arrow_right:
Prophage
:warning:
Prophage
infected bacteria :arrow_right:
Lysogen
:check: HIV is an example of temperate infection to Human cell (host cell) :arrow_right:
HIV is prophage :arrow_forward: lysogen
the two cycles can overlap