Unfortunately we all get sick once and a while, most likely because our cells were invaded by a virus. One tiny virus can make you horribly sick. But it’s actually not the virus directly that makes us have a fever, tummy ache, hurting chest, congestion…but the response given in defense by the immune system that makes us feel sick.
Are viruses alive? We can use something called the 3R’s and the Big O to find out. The three R’s and the big O stand for reproduction, response, refuel and organization. To be considered alive the thing has to be able to do all these things. A virus cannot replicate (reproduce) without help, they cannot refuel, they cannot respond, although they are organized. Therefore, they are not considered alive. They are like little robots.
A bacteriophage (a type of virus) is shaped with a “head” containing the genome, DNA and RNA, and then a cylindrical “body” and then “arms and legs” of proteins. (See picture for reference). This type of virus attaches to the cell and injects the viral genome into the healthy cell. The viral DNA then attaches to the healthy one and they will replicate causing the creation of more viral cells.
There are two ways that this replication can happen. Through the Lytic Cycle, the cell is induced to make viral proteins that are then released to affect more cells. Through the Hysogenic Cycle, the two DNA’s replicate until they trigger the Lytic Cycle. (This happens through the process of a cell splitting/replicating but with part of the DNA being viral. See this essay.)
Animal proteins enter cells differently. The membrane of the cell lets the virus in—the virus is a “ball” containing the viral RNA and enzymes. The RNA is then released into the endoplasmic reticulum, which triggers the replication of the virus’ RNA that is released to attack more cells. However, in this version of a ‘viral attack’, the cell and DNA are not altered. They just serve as a place where the virus can replicate itself.
As you can see, it only takes one virus to start a chain of continuous replication of the virus that will attack more and more cells.
There are different effects an animal virus can have. They obviously can damage and destroy cells, they can produce toxins to harm you and they may cause mutations leading to cancer (through altering the cell replication process). Viruses also trigger the immune system to respond to them. This leads the immune system to destroy the virus and all affected cells. This is what makes you feel sick.
In defense to viruses, interferons are released by the infected cells to trigger a protection by the immune system against further virus attacks. The interferons also interfere with the virus replication. Restriction enzymes also help in prevention by detecting “foreign” genetic material (viral genome) and they cut off the replication of the viral DNA with the healthy DNA so that the virus can’t spread. All this helps prevent the spreading of a virus, but they are still extremely hard to stop even with the help of antibiotics. (Common sense tells me that antibiotics are taken to trigger many of these reactions against a virus, as well as preventing the virus itself, and that’s why we take it. I am not sure about this though.)
There are several variations of a virus like a viroid. These are short strands of RNA that invade plants and inhibit their growth. The different variations of the animal virus are what cause all the human diseases, from a small cold to something much worse.
As a small note, I would like to say that I know I used a lot of scientific terms without explaining what they were. I encourage you to look these up or you can leave me a comment and I would be happy to explain them to you. Thanks!