Viruses have two main components. The first is the delivery package. This is the element that is capable of delivering a payload into the interior of a cell. The second is the genetic code that hijacks a cell's normal functioning to produce more viruses. Viruses have a genetic component, either RNA or DNA, which contain instructions for building their viral envelopes. The genetic material is as vulnerable to damage as cellular DNA.
Prions are a single component. They are proteins with the same amino acid sequence as a protein normally produced by an organism. Except they have been misfolded. The geometry of the misfolded protein is such that it becomes a catalyst to reproduce the same misfolding error. There are no "brains" in them. They can arise entirely accidentally. They're a bit like the ice-nine from Vonnegut's _Cat's Cradle_, in which a crystal of a novel form of solid water that melts at a higher temperature can recruit liquid water to grow the crystal without limit. Each individual prion can misfold any number of same-sequenced amino acid chains.
And like the ice-nine, which melted at a temperature above human body temperature, the prion may be able to survive through more extreme conditions than other forms of the protein.
In the best case scenario, the prion does little more than cause a deficiency of the normally-folded protein forms in the body. In the worst-case scenario, it poisons some other process within the body in its misfolded form.
Pet peeve of mine, but it looks like you slept through English class as well. The plural of "virus" in English is "viruses". "virus" in latin is a mass word and has no plural, like "sugar" and "air".
Your perscriptivism here seems misguided then, because if virus is a mass word we shouldn't be saying viruses either: just "virus". And anyway, if we absolutely had to express a plurality of virus, it would be "vira".
Anyway, this is hackernews.
For those of us who grew up in internet hacking communities of the early 90's "virii" was the plural form in the lingua franca. As a descriptivist of great habit, I will continue to use that form.
I am actually a descriptivist myself, but the prescriptive approach usually works best when trying to convince people how to write. Apparently not so in this case.
How about this argument then: "virii" is f*ckin ugly? No? Darn. :-)
Just because a noun is a mass word in one language, it doesn't mean it has to be in other languages that have borrowed the word.
For example, in my language, "lego" is a mass word, and to make a plural you would have to say something like "pieces of lego", but in English, the plural of "lego" is "legos".
My understanding is that the fact that viruses are not alive is more of a convention, similar to Pluto not being a planet. This is more of a question than a statement, I would love it if somebody with some knowledge on the matter could chime in.
life, species, organism.... all are leaky abstractions.
[There's a "species" that spread around the Andes and eventually reached itself on the other side---and could no longer breeed with "itself". Genes could still in theory travel all the way around and back to the discontinuous point, however.]
Having thought about this a lot, the best definition of life I've been able to come up with is as follows:
An object is considered to be alive if it consumes energy to create or maintain its own order (in opposition to the general effect of the second law of thermodynamics in the wider system in which it finds itself).
Bacteria can do things on their own (say, swim in water). Viruses can't do anything without a host's reproduction engine (like a program which can't do anything without a computer to run on). Prions are misshapen proteins which tend to damage other proteins such that the result is the same misshapen, and thus duplicating, form.
I think what was meant is that on the grand scale of "aliveness" viruses are more alive than prions. Viruses have DNA, they actively seek out host cells to hijack so they can reproduce, etc. Prions are much simpler and aren't alive at all. They're just accidentally self-reproducing patterns, basically. They don't have DNA, they don't make any specific effort to reproduce, they just "happen" from weirdly broken matter bumping together.
