! Marie!A.!Pamatmat!BIOS!350,!Professor!Gibbons,!Spring!‘19!
!
BIOS%350%Unit%2%Exam%
%
The!Viral!Life!Cycle!
!
-virulent!phages!typically!lead!to!immediate!death!of!the!cell!or!establish!latent!or!
chronic!infection!
-temperate!phages:!become!part!of!a!host!chromosome!and!are!replicated!with!the!cell!
genome!until!such!time!as!they!induced!to!make!newly!assembled!viruses!
!
Lytic!Cycle!
! -the!cycle!goes!through!the!step!in!a!particular!order:!a!step!by!step!process!
! -5!stages!om!bacteriophage!lytic!cycle:!
1.!Attachment!(absorption):!the!phage!interacts!with!specific!bacterial!
receptors.!Interaction!surface!of!host!cell!and!the!virus!
2.!Penetration:!occurs!through!contraction!of!the!tail!sheath,!which!acts!
like!a!hypodermic!needle!to!inject!the!viral!genome!through!the!cell!wall!
and!membrane.!Once!the!bacteriophage!attaches!to!the!receptor!it!
causes!some!conformational!changes!
3.!Biosynthesis:!the!virus!synthesizes!virus-!encoded!endonucleases!to!
degrade!the!bacterial!chromosome.!Will!be!able!to!code!for!the!next!
generation!of!viron,!copying!of!genome.!It!will!make!the!genomes!for!the!
next!generation!of!viruses.!The!capsid!and!DNA!made!in!separate!chunks,!
but!will!end!up!being!merged!together!later!on.!!
4.!Maturation!(assembly!step):!new!phage!particles!get!assembled.!All!
the!pieces!get!connected!together.!Not!100%!perfect!in!maturation!step,!
but!will!produce!a!lot!of!virons.!!
5.!Lysis:!mature!viruses!burst!out!of!the!host!cell!in!a!process!called!lysis.!
The!viral!DNA!will!code!for!a!large!amount!of!DNA!that!will!be!released!
from!the!cell!when!the!cell!wall!gets!damaged.!The!viral!genome!is!coding!
for!genome!for!a!larger!amount.!Cell!will!lyse!or!burst!and!release!the!
phages.!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !
!
!
!
,! Marie!A.!Pamatmat!BIOS!350,!Professor!Gibbons,!Spring!‘19!
!
Lysogenic!Cycle!!
! -phage!genome!also!enters!the!cell!through!attachment!and!penetration!
! -lysogeny:!the!process!in!which!a!bacterium!is!infected!by!a!temperate!phage!
-lysogenic!conversion:!the!presence!of!the!phage!may!alter!the!phenotype!of!the!
bacterium,!since!it!can!bring!in!extra!genes!
-induction:!results!in!the!excision!of!the!viral!genome!from!the!host!chromosome!
-very!specific!attack!for!the!virus,!temporary!execution!style.!
-have!a!period!of!time!where!the!host!can!be!infected!by!the!genome,!but!the!
host!is!still!alive!and!it!can!reproduce!itself!
! ! -has!the!same!steps!as!lytic!cycle!but!has!a!few!more!steps!
! -the!viral!DNA!joins!up!with!the!host!cell!DNA!(establishing!prophage)!
! ! -it!will!not!be!directing!any!activity!to!replicate!the!viruses!
! ! -won’t!be!causing!harm!to!the!host!
! ! -all!the!daughter!cell!will!contain!prophage!itself!
-excised:!the!host!cell!is!dying!and!the!virus!is!dying.!Cutting!back!out!the!prophage,!the!
environment!was!a!bad!growth!environment.!!
!
!
!
Terms!that!come!in!handy!
◦ Prophage:!Viral!DNA!integrated!into!host!cell!DNA!
◦ Lysogen:!Bacteria!once!prophage!is!established!
◦ Lysogeny:!Process!where!lysogenic!phage!infects!bacterial!host!
◦ Lysogenic!conversion:!Lysogen!takes!on!new!characteristics!due!to!prophage!genes!!
◦ Often!can!produce!toxins!it!couldn’t!make!before!
◦ Induction:!Environmental!change!that!leads!to!prophage!excision!
!
!
!
!
!
, ! Marie!A.!Pamatmat!BIOS!350,!Professor!Gibbons,!Spring!‘19!
!
Transduction!
!
-occurs!when!a!bacteriophage!transfers!bacterial!DNA!from!one!bacterium!to!another!
during!sequential!infections!
! -2!Types:!
! ! -generalized!
! ! -specialized!
-the!virus!hijacks!the!host!cell,!degrades!the!host!chromosomes!and!makes!more!
viral!genomes!!
-the!asexual!transfer!of!genetic!information!allows!for!DNA!recombination!to!
occur,!thus!providing!the!new!host!with!new!genes!
-generalized!transduction:!occurs!when!a!random!piece!of!bacterial!
chromosomal!DNA!is!transferred!by!the!phage!during!lytic!cycle!
-specialized!transduction:!occurs!at!the!end!of!the!lysogenic!cycle,!when!
the!prophage!is!excised!and!the!bacteriophage!enters!the!lytic!cycle.!
-when!excision!the!viral!genome!is!just!to!cut!but!also!the!host!
genome!maturation!still!occurs!the!same!!
-when!they!infect!the!next!host!they!penetrate!the!genome,!they!
inject!the!previous!bacteria’s!genome,!and!can!cause!changes!in!
the!new!host!cell!
-delivers!bacteria!genes!to!another!bacteria!
-not!just!mutations!that!change!the!genome!of!the!
bacteria!
-bacteria!permeable!enough=!transformation!
! ! -5!steps!in!Specialized!Transduction!
! ! ! 1.!Viral!attachment!&!penetration:!the!phage!infects!the!cell!
! ! ! 2.!Integration:!the!phage!DNA!becomes!incorporated!into!host!genome!
3.!Excision:!the!phage!is!excised!from!the!bacterial!chromosome!along!
with!a!short!piece!of!bacterial!DNA.!The!DNA!is!then!packaged!into!newly!
formed!capsids.!
4.!Infection:!Phage!containing!both!viral!and!bacterial!DNA!infect!the!new!
host!cell!
5.!Recombination:!the!phage!DNA!along!with!the!attached!bacterial!DNA!
are!now!incorporated!into!the!new!cell.!!
!
!
!
BIOS%350%Unit%2%Exam%
%
The!Viral!Life!Cycle!
!
-virulent!phages!typically!lead!to!immediate!death!of!the!cell!or!establish!latent!or!
chronic!infection!
-temperate!phages:!become!part!of!a!host!chromosome!and!are!replicated!with!the!cell!
genome!until!such!time!as!they!induced!to!make!newly!assembled!viruses!
!
Lytic!Cycle!
! -the!cycle!goes!through!the!step!in!a!particular!order:!a!step!by!step!process!
! -5!stages!om!bacteriophage!lytic!cycle:!
1.!Attachment!(absorption):!the!phage!interacts!with!specific!bacterial!
receptors.!Interaction!surface!of!host!cell!and!the!virus!
2.!Penetration:!occurs!through!contraction!of!the!tail!sheath,!which!acts!
like!a!hypodermic!needle!to!inject!the!viral!genome!through!the!cell!wall!
and!membrane.!Once!the!bacteriophage!attaches!to!the!receptor!it!
causes!some!conformational!changes!
3.!Biosynthesis:!the!virus!synthesizes!virus-!encoded!endonucleases!to!
degrade!the!bacterial!chromosome.!Will!be!able!to!code!for!the!next!
generation!of!viron,!copying!of!genome.!It!will!make!the!genomes!for!the!
next!generation!of!viruses.!The!capsid!and!DNA!made!in!separate!chunks,!
but!will!end!up!being!merged!together!later!on.!!
4.!Maturation!(assembly!step):!new!phage!particles!get!assembled.!All!
the!pieces!get!connected!together.!Not!100%!perfect!in!maturation!step,!
but!will!produce!a!lot!of!virons.!!
5.!Lysis:!mature!viruses!burst!out!of!the!host!cell!in!a!process!called!lysis.!
The!viral!DNA!will!code!for!a!large!amount!of!DNA!that!will!be!released!
from!the!cell!when!the!cell!wall!gets!damaged.!The!viral!genome!is!coding!
for!genome!for!a!larger!amount.!Cell!will!lyse!or!burst!and!release!the!
phages.!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !
!
!
!
,! Marie!A.!Pamatmat!BIOS!350,!Professor!Gibbons,!Spring!‘19!
!
Lysogenic!Cycle!!
! -phage!genome!also!enters!the!cell!through!attachment!and!penetration!
! -lysogeny:!the!process!in!which!a!bacterium!is!infected!by!a!temperate!phage!
-lysogenic!conversion:!the!presence!of!the!phage!may!alter!the!phenotype!of!the!
bacterium,!since!it!can!bring!in!extra!genes!
-induction:!results!in!the!excision!of!the!viral!genome!from!the!host!chromosome!
-very!specific!attack!for!the!virus,!temporary!execution!style.!
-have!a!period!of!time!where!the!host!can!be!infected!by!the!genome,!but!the!
host!is!still!alive!and!it!can!reproduce!itself!
! ! -has!the!same!steps!as!lytic!cycle!but!has!a!few!more!steps!
! -the!viral!DNA!joins!up!with!the!host!cell!DNA!(establishing!prophage)!
! ! -it!will!not!be!directing!any!activity!to!replicate!the!viruses!
! ! -won’t!be!causing!harm!to!the!host!
! ! -all!the!daughter!cell!will!contain!prophage!itself!
-excised:!the!host!cell!is!dying!and!the!virus!is!dying.!Cutting!back!out!the!prophage,!the!
environment!was!a!bad!growth!environment.!!
!
!
!
Terms!that!come!in!handy!
◦ Prophage:!Viral!DNA!integrated!into!host!cell!DNA!
◦ Lysogen:!Bacteria!once!prophage!is!established!
◦ Lysogeny:!Process!where!lysogenic!phage!infects!bacterial!host!
◦ Lysogenic!conversion:!Lysogen!takes!on!new!characteristics!due!to!prophage!genes!!
◦ Often!can!produce!toxins!it!couldn’t!make!before!
◦ Induction:!Environmental!change!that!leads!to!prophage!excision!
!
!
!
!
!
, ! Marie!A.!Pamatmat!BIOS!350,!Professor!Gibbons,!Spring!‘19!
!
Transduction!
!
-occurs!when!a!bacteriophage!transfers!bacterial!DNA!from!one!bacterium!to!another!
during!sequential!infections!
! -2!Types:!
! ! -generalized!
! ! -specialized!
-the!virus!hijacks!the!host!cell,!degrades!the!host!chromosomes!and!makes!more!
viral!genomes!!
-the!asexual!transfer!of!genetic!information!allows!for!DNA!recombination!to!
occur,!thus!providing!the!new!host!with!new!genes!
-generalized!transduction:!occurs!when!a!random!piece!of!bacterial!
chromosomal!DNA!is!transferred!by!the!phage!during!lytic!cycle!
-specialized!transduction:!occurs!at!the!end!of!the!lysogenic!cycle,!when!
the!prophage!is!excised!and!the!bacteriophage!enters!the!lytic!cycle.!
-when!excision!the!viral!genome!is!just!to!cut!but!also!the!host!
genome!maturation!still!occurs!the!same!!
-when!they!infect!the!next!host!they!penetrate!the!genome,!they!
inject!the!previous!bacteria’s!genome,!and!can!cause!changes!in!
the!new!host!cell!
-delivers!bacteria!genes!to!another!bacteria!
-not!just!mutations!that!change!the!genome!of!the!
bacteria!
-bacteria!permeable!enough=!transformation!
! ! -5!steps!in!Specialized!Transduction!
! ! ! 1.!Viral!attachment!&!penetration:!the!phage!infects!the!cell!
! ! ! 2.!Integration:!the!phage!DNA!becomes!incorporated!into!host!genome!
3.!Excision:!the!phage!is!excised!from!the!bacterial!chromosome!along!
with!a!short!piece!of!bacterial!DNA.!The!DNA!is!then!packaged!into!newly!
formed!capsids.!
4.!Infection:!Phage!containing!both!viral!and!bacterial!DNA!infect!the!new!
host!cell!
5.!Recombination:!the!phage!DNA!along!with!the!attached!bacterial!DNA!
are!now!incorporated!into!the!new!cell.!!
!
!
