Typically, when I taught the characteristics of life I would mention that viruses mess with our understanding of life but wouldn’t go much further, it was outside the scope of the course. For obvious reasons — ie the current covid-19 pandemic– I’ve been thinking about the tiny little virus and its tenacity for life, wrapped up in a package that defies our understanding of life.
So, how do viruses mess with the characteristics of life? The biggest issue is the ability to reproduce. You see, a virus can’t reproduce on its own. One of the big requirements for reproducing is replicating the genetic material. But a virus can’t replicate its own genetic material.
Thre are two types of genetic material. DNA acts as the blueprint for everything the organism needs to make. Some viruses have DNA, but others, including coronaviruses, have a related form of genetic material called RNA. There are differences between DNA and RNA, but broadly DNA is the idea while RNA is the actual implementation plan. Both DNA and RNA viruses need to hijack a host’s cell machinery in order to replicate.
So, a virus enters a host cell and hijacks the machinery so that the cell makes more viruses rather than its normal proteins. This of course can have some impacts but most of the symptoms we experience when we have a viral infection are actually caused by our body’s immune response: the things our bodies do to get rid of a virus are the things that make us feel sick.
One purpose of a fever is thought to be an attempt to kill off bacteria or viruses. A fever is caused by chemicals caused pyrogens. Harper, et al (2018) also found that some genes are up-regulated (meaning they increase production) by an increase in temperature associated with a fever. These genes are largely associated with inflammation which is another immune response which tries to isolate the invader and attract other cells that will (hopefully) fight the infection.
Something to keep in mind is that it isn’t in a viruses’ best interests to kill its host. The virus is not intentionally causing harm, it is trying to survive. Which brings me back to the characteristics of life. We struggle to understand that which isn’t like us, we struggle then to understand viruses. But viruses share something with all living things that will never end up in a science textbook: everything alive takes actions in order to continue to exist, guided by conscious intention or not.