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chances are in your life you've had the
common cold before it can cause sneezing
and coughing and can make you feel awful
the worst thing about the common cold is
that you can take medications to help
with the symptoms but you really can't
treat the actual cold with antibiotics
like you would a strep throat infection
or an infected tooth why well let's talk
about what causes it a virus the common
cold is caused by a virus while all
living things are made of one or more
cells see the modern cell theory viruses
are not cells viruses aren't technically
classified as living things since they
lack many characteristics of life but
there is some debate in calling them
non-living as well
medications like antibiotics attack
bacteria like e coli which are living
cells anti-fungal medications can be
used on fungi like athlete's foot which
are made of living cells viruses are not
bacteria or fungi you can't classify a
virus as a prokaryote or a eukaryote
either because it's not a cell
so what is their structure like first of
all viruses are much much smaller than
cells you typically are going to need an
electron microscope in order to see a
virus viruses come in many shapes our
favorite one to draw is the
bacteriophage it sounds very fancy but
it's a type of virus that tends to
attack bacteria despite this being our
favorite to draw know that the shape of
viruses vary greatly one thing all
viruses have in common is that they have
some type of genetic material this
genetic material can be in the form of
dna or rna viruses usually have some
kind of protein coat also known as a
capsid the capsid can protect the dna or
rna genetic material viruses can also
have other structures
some viruses package special enzymes
with them some viruses have an outer
envelope these additions can be useful
to the virus in virus replication
one thing that makes virus replication
or reproduction unique is that they
can't replicate without a host
and it's there reproducing that tends to
be a problem for its host whether the
host is you in the case of the common
cold or an insect plant this bacterium
viruses tend to be very specific for the
host that they're going to infect
but anything that is alive can be a host
because cells have the machinery that
viruses need in order to replicate we're
going to talk about two types of viral
replication cycles the first one is the
lytic cycle in the lytic cycle the virus
remember very selective attaches to a
host cell it often binds to a receptor
that this cell has which gives it access
to attach the virus can inject either
its dna or rna depending on what kind of
genetic material it has
into the cell
some types of viruses are actually taken
inside the cell themselves now you would
think that the cell would notice viral
dna or rna or an entire virus that has
been taken in but in many cases it does
not it takes the genetic material from
the virus and it starts following the
instructions which in this case is very
bad because the instructions tell it to
make copies of the virus the cell uses
its own resources to start building it
starts making so many copies of the
virus that it can cause the cell
membrane of the host to rupture explode
rice so what happens is now that these
new viral copies they can get out of the
cell and go and infect other cells this
is known as the lytic cycle by the way
the lysing of the cell membrane is a
very bad thing for the cell the cell
cannot survive without its cell membrane
the other cycle is called the lysogenic
cycle and i'd like to remember this is
the longer word so i like to think of
this as the longer sneaky cycle viruses
that go through this cycle tend to do
the same thing at the beginning they
inject their genetic material but this
time the genetic material stays hidden
in the host genetic material what
happens is that when the host makes new
cells it replicates its own genetic
material and the viral genetic material
then those daughter cells make new cells
and they also replicate their own
genetic material and the viral genetic
material and so on this is the lysogenic
cycle
that may not seem like a problem but it
really becomes one if the virus gets
triggered to go into the lytic cycle
from that point because then all those
cells that have the viral genetic
material can start assembling viruses
and as far as what triggers it to go
into the lytic cycle it can vary it
could be a chemical trigger for example
or a lack of food for the host
going back to the common cold a lot of
times it has to run its course your
immune system will typically take care
of it and medications can help with the
symptoms that they don't feel as bad but
unfortunately some viruses are extremely
complicated like hiv a virus that can
lead to aids like most viruses it is
very specific it binds to a cd4
glycoprotein that is found on the
surface of specific cells such as helper
t cells
the problem about this particular target
is that helper t cells play an important
role in protecting the body in the
immune system
since hiv goes after these immune cells
it can make a person that is infected
with hiv vulnerable to other infections
there are medications that have been
developed to help keep hiv from
replicating as quickly and there
continues to be research into looking
into ways to keep the virus from
attaching because if the virus can't
attach it can't insert its genetic
material a problem that continues to be
a challenge is that many viruses
including hiv can mutate so a treatment
developed against a certain virus type
may not work on a mutated form
so with our talk about viruses you might
wonder is there anything positive about
viruses
well some viruses can play a useful role
in gene therapy definitely something to
explore more
also remember how we mentioned that
viruses can go after other organisms
like insects for example
a virus that targets pest insects could
be an alternative to a chemical
pesticide one such example virus that
you may want to explore is the nuclear
polyhedrosis virus
still it's important to consider that
whenever talking about any kind of
pesticide chemical or viral there could
be consequences in the ecosystem
well that's it for the amoeba sisters
and we remind you to stay curious
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bye