The United Colours of Virus-ton
We all get sick all the time, and when we do, it's usually due to one of two reasons: you were infected by a bacterium or virus, or because you fell in love with someone out of your league. This chapter is mostly going to talk about the former. If you want to know about love, you should listen to more Beatles songs. People have known about bacteria for centuries because they are visible by most microscopes. However, viruses are a fairly recent discovery. As for monkeys, well, science may never know where they came from, but our best guess is that they're just tiny robots in costumes. Viruses, however, have been hard to study for 3 reasons:
- Viruses are very small and can only be seen on special microscopes –while they never get on rollercoasters, they are always comfortable on airplane seats.
- Viruses cannot grow or replicate without taking over another cell – they make the worst roommates.
- Viruses are very diverse – they take offense to the term "virus," and prefer to be called "Virus Americans."
Because viruses are very diverse, it is very hard to define the features of a virus. An individual virus is also called a "virion" or virus particle, and it must have 2 elements: a nucleic acid genome (either DNA or RNA), and a protective coat. This coat can either be a protein capsid, or capsid and lipid bilayer, called an envelope. NOTE: This should not be used for actual mail. We tried, and now are no longer allowed near FedEx employees.
FIGURE 1: Prototypical virus structure
The cartoon above shows that there are two types of viruses: those with envelopes, and those without, called naked viruses. Wait. You are 18, right? Otherwise, just skip ahead to the non-naked viruses section until you're ready. You know what? We'll let you have a peek at naked viruses in the anyway…just don't rat us out. WE DON'T LIKE RATS.
You can take all viruses and split them into various types based upon type of genome (RNA vs. DNA, segmented vs. non-segmented), how it is spread (oral-fecal, bloodborne, saliva), type of capsid (helical vs. icosahedron), host type (animal vs. bacterial/archaea).
We'll go through all of these things, so don't worry about the words now, but just know that viruses are very diverse. Finally, this chapter is mostly going to talk about animal viruses, specifically those viruses that infect humans. Which is fortunate, as the non-human infecting viruses are all freakish looking. (such as the bacteriophages described in the Capsid Structure section).