A beautifully written article in the NY Times.
Viruses are different from all other life forms. Whereas the rest of us whether were talking humans, mushrooms, petunias or bacteria are made of one or more cells, viruses are not. They havent got a cell, with all that machinery for detecting, and interacting with, the outside world. Instead, viruses are just sets of genes packed inside a capsule, or capsid, that is usually made out of protein molecules. (Depending on the virus, the capsid will take one of a number of forms. Some look like 20-sided dice. Others resemble moon landers tiny containers on a set of legs.)
Many viruses have unorthodox genetics: instead of using DNA to store their genetic information, they use a related molecule, RNA. Moreover, while in its capsid, a virus is inert: it does not eat, it does not breathe. And all viruses are parasites. That is, they cannot reproduce make more viruses unless they are within the cell of a proper organism.
One is that viruses play a fundamental role in regulating the food chain. This is because death-by-virus is different from death-by-predator. When a predator kills a microbe, it consumes it: the microbes cell is incorporated into the predators body. In contrast, when a virus kills a microbe, the microbes cell bursts open, or lyses, releasing new viruses and a lot of cellular debris back into the environment. This debris can then be consumed by other microbes. In other words, by lysing their victims, viruses are constantly making food available to other life forms.
As you lie in bed with flu, or sit at your desk sneezing with a cold, it may be hard to appreciate the wonder of viruses. Yet, just as much of the beauty we see around us the length of a hummingbirds beak, the speed of the gazelle is an evolved response to other life forms (the depth of a flower, the leap of a cheetah), so too at the level of the cell, much of the intricacy we see is due to evolution in response to viruses. Its an intricacy that we are still unraveling: we have much to learn in the years ahead. Perhaps one day, well be able to use our knowledge to beat viruses at their own game.