so let's talk about viral replication
since we know that viruses are made of
only proteins and one type of nucleic
acid which means they have no organelles
to make copies of themselves with they
have to get inside other cells in order
to use their ATP and their organelles to
make copies of themselves so first step
get inside that cell and I'm just going
to mention a few things for review so
remember there are three ways of getting
into a cell you know one of the ways of
getting in is that bacteria phages they
literally just inject their genetic
material inside of the cell whereas
every other type of virus uses one of
two ways they if they're not envelopes
they they trick the cells receptors into
letting them in or if their envelope
they can either use that receptor trick
or they directly fuse with the membrane
and once that genetic material is inside
of the cell the virus has hacked in and
it's ready to do a takeover but here's
where it makes a choice it's kind of
either impatient and ready to get going
to copy itself or it sits back and says
you know what I'd rather sit and wait
until I'm ready to take over so let's
just draw these two possibilities out to
see what happens
and with the first choice the the
impatient virus goes ahead and takes
over the cells machinery they're their
ATP ribosomes nucleic acids amino acids
to start making copies of the virus's
genetic material which again can be RNA
or DNA and also the viruses proteins to
make their protein coat and these will
self assemble that means they just come
together on their own to form fully
functional viruses and because it keeps
making more and more and more of these
it will eventually force the cell to
lyse or break open and once it breaks
open all of these viruses are released
into the environment and if there are
other cells nearby then this army can
start marching out to infect to hack
into those nearby cells and create more
armies so this makes a lot of sense if
you have a lot of hosts around and your
goal is to just create the biggest army
in the fastest way possible and so
that's the impatient virus so what about
the other option the other option is
where the virus decides it's just going
to sneak in and hitch a ride it thinks
that the bacteria seems to be doing fine
on its own maybe there aren't other
hosts nearby so there's no reason to
kill off the host because lie sing it
would kill the host so we don't want
that we're just going to keep the host
alive and in order to sneak in and and
let the bacteria do its thing while it's
waiting it's going to combine with the
hosts genetic information so that the
hosts really can't tell that it's there
it's basically quietly sitting there
because it's repressed there are
repressor genes on this virus so it's
not expressed it's not transcribed so
it's not doing anything and this is
called a pro virus or you might also
hear the word Pro fade and again because
it's not doing anything this is called a
dormant or latent phase so the bacteria
just does its own thing
it continues replicating and of course
the virus is already there so it will
continue to replicate so it will
replicate when the bacteria does because
it's part of its genome but about one in
10,000 times that this happens or if
something happens like the bacteria is
exposed to UV light or something well in
any case there's something that weakens
that repressor gene that we talked about
on that virus so it's no longer quiet
and the hosts genome like most other
genomes will start wanting to repair
itself
that means it will cut out to try to
repair its genome it will excise out
part of its DNA that just happens to be
the virus and now the virus is active
it's ready to make copies of itself lyse
the cell and get its army out into
infecting other cells so the official
terms for the impatient method is the
lytic cycle and the hitch a ride method
is called the lysogenic cycle so now you
should have a good idea of what the
lytic and lysogenic cycles are in viral
replication