Captions are on! To turn off, click CC at bottom right. Follow us on Twitter (@AmoebaSisters) or Facebook! Chances are in your life, you’ve had the
common cold before. The cold is extremely common. You know, it causes the sneezing and
the coughing and just makes you feel awful. The worst thing about the cold is that you
can take medications to help with the symptoms, but you really can’t treat the actual cold.
You can’t really get rid of what causes it. Why is that? The reason for this is because most colds
are caused by viruses. We’ve talked before about antibiotics; they only work on bacteria.
Viruses are definitely NOT bacteria. So antibiotics have no effect on viruses. In fact, viruses
aren’t even cells at all. You can’t say that viruses are a prokaryote or a eukaryote.
It’s not a cell. It doesn’t have a cell membrane like all cells have; it doesn’t
have a lot of cell components. It’s a non-living structure. In fact, viruses can’t even reproduce
on their own. So, viruses aren’t even alive, which makes them very difficult to treat.
Let’s talk about what they actually have. What IS their structure? One thing all viruses have in common is that
they have some type of genetic material. This does not mean they can reproduce on their
own, but they are going to use their genetic material and force their host to reproduce
themselves. This genetic material, for some viruses, is in the form of DNA. For other viruses, it’s RNA. Viruses
also usually have some kind protein coat, also known as a capsid. Capsid is a vocab word
to think of that can protect that DNA or RNA genetic material. Another thing to mention
is that viruses are very, very small; they are MUCH smaller than bacteria. You typically
are going to need an electron microscope in order to see a virus. It’s very, very small. Viruses can also contain other structures.
Some of them package special enzymes with them. Some viruses have an outer envelope.
There are different varieties of what viruses can have, but they main thing is that they
have genetic material and they typically have some kind of protein coat, also known as a
capsid. Now, viruses are very, very specific. So you’ll want to think of them as picky.
Usually, viruses have specific types of cells that they go after. So let’s talk about viral reproduction,
because we did mention that they can’t reproduce on their own and their very, very specific
for the host that they’re going to go infect. So the first cycle of the two we’re going
to talk about is the lytic cycle. In the lytic cycle, the virus (remember they’re very selective)
attaches to a host cell, and it’s going to inject either its DNA or RNA, depending
on what kind of genetic material it has, into the cell. You would think the cell would notice
this, but in many cases it does not. It takes that genetic material and it starts following
the instructions, which in this case is very bad. In this case it makes copies of the virus.
It starts making so many copies of the virus that usually it’s going to cause the cell
membrane of the host to rupture, explode, lyse! So what happens is now these new viral
copies get out of the cell, and they go and infect other cells. This is very bad. 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.
It’s definitely not a good thing for a cell. The other cycle is called the lysogenic cycle,
and I like to remember this is the longer word so I like to think of this as the longer,
sneaky cycle. A lot of times when we’re talking about this cycle, we’re talking
about a special kind of virus called a bacteriophage. It sounds very fancy, but what it means is
that it is a virus that goes after bacteria. In many cases, when we’re talking about
a lysogenic virus, this is what we’re talking about. These types of viruses that go through
this cycle, they do kind of the same thing at the beginning. They inject their genetic
material, but this time, the genetic material stays hidden in the host DNA. What happens
is that when the host replicates it also replicates the viral DNA. Eventually, what can happen
is that it can be triggered to go into the lytic cycle and then the virus can start being
assembled and lyse out of the cell. In the meantime, whenever it’s during the lysogenic
cycle, it’s kind of hidden in there. It’s kind of a sneaky kind of thing. As far as
what triggers as what triggers it to go into the lytic cycle, it can be a variety of things.
Scientists are still doing a lot of studies about this. Sometimes we notice they are environmental
triggers like UV radiation or chemical triggers, but it can cause the virus to suddenly switch
into the lytic cycle. So going back to the cold, which again is
typically caused by a virus, a lot of times it has to run its course. Your immune system
will take care of it. Some viruses are extremely complicated, like HIV, a virus that can lead to AIDS. The host that it goes after are immune cells. By going after
immune cells, it makes you very vulnerable to other infections. In fact, for someone who has HIV, the common cold could be very detrimental to their health. It’s something that
scientists are really researching to try to treat. It’s difficult, too, because HIV
is a virus that tends to mutate quickly and so if the medications are very selective against
one specific type of virus and the virus mutates, it makes it difficult to treat. So with our talk today about viruses, you
might wonder, “Is there anything positive about viruses?” Well, viruses do play a
major role right now in gene therapy. It’s a very big field right now that is growing
with research. Viruses do play a big role with that. Also, scientists are looking for
ways to manipulate or engineer viruses; for example, there is a type of virus that goes
after insects. It’s called the Nuclear Polyhedrosis virus. I highly encourage you to look it up.
This virus is very selective; it goes after certain insects. However, if it could be targeted
to a certain type of insects, the types that eat your crops, then it could be a great form
of a pesticide. The only problem is that whenever you add some kind of pesticide, whether chemical
or viral, there can be major consequences in the ecosystem. When we get to ecology,
we will talk about that. Viruses are a major component of scientific research right now.
That’s it for the Amoeba Sisters, and we remind you to stay curious.