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 their 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 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, lyse.
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 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's 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 is. It really becomes one if the virus gets triggered to go into the lytic cycle from that point.
Because then all those cells that had 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 so 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 polyhidrosis 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.