[blakestyger]

There seems to be a concensus that viruses are not 'alive'.
I'd like to know - what do you think? Reasons please.

[Madidus_Scientia]

I suppose this depends on how strict your definitions of life are. I can see how people would argue this, since a virus is quite simple and tiny compared to a bacteria, it is basically just some genetic material packaged in a membrane. One of the common things people say that something alive does is to replicate itself, well a virus does effectively do this but not by its own mechanisms - it inserts its own genetic material into a host cell and the host cell does all the work of replicating the virus. The virus itself does not consume materials to grow and divide like a bacteria does. Actually, it does bugger all except float around, it doesn't even need to respire. So i guess you could think of it as some self replicating molecule instead of life. It could not exist on its own without other life to infect, even if it did have a store of organic food.

Mad Cow disease is a similar concept, this isn't actually caused by any virus, merely a molecule of protein, that when it comes into contact with another molecule of protein that is similar to it but is part of the organisms normal functions (its found in the brain), it binds to it and moulds it to the same shape as the mad cow disease protein. this protein then in turn encounters other proteins and before you know it the protein has replicated exponentially. I think this is even harder to call life.

But a virus definitely is something that replicates (even if its not self-replicating) and evolves, I myself would say it is life, just at its most basic levels. But when you argue whether its alive or not, i think what you're really argueing about is your definition of life.

[Carol-A]

But when you argue whether its alive or not, i think what you're really argueing about is your definition of life.

I totally agree with this!!

[another_someone]

since a virus is quite simple and tiny compared to a bacteria,

even this is not inevitably so, although it is commonly so.

http://en.wikipedia.org/wiki/Mimivirus

Mimivirus is a viral genus containing a single identified species named Acanthamoeba polyphaga mimivirus (APMV). In colloquial speech, APMV is more commonly referred to as just “mimivirus”. It has the largest capsid diameter of all known viruses, as well as a large and complex genome compared to other viruses. Though knowledge of the virus is relatively limited, the discovery of the virus excited many people due to the implications of its complex nature, with people hailing it as everything from a new domain of life to a missing link between viruses and bacteria.
The mimivirus genome is a linear, double-stranded molecule of DNA roughly 1.2 million base pairs in length. This makes it the largest viral genome in scientific knowledge, outstripping the next-largest virus genome of the myovirus Bacillus phage G by a little over double. In addition, it is larger than at least 30 cellular organisms.

In addition to the large size of the genome, mimivirus possesses an estimated 911 protein-coding genes, far exceeding the minimum 4 genes required for viruses to exist (c.f. MS2 and Qβ viruses). Analysis of its genome revealed the presence of genes not seen in any other viruses, including aminoacyl tRNA synthetases, and other genes previously thought only to be encoded by cellular organisms. Like other large DNA viruses, mimivirus contains several genes for sugar, lipid and amino acid metabolism, as well as some metabolic genes not found in any other virus (M. Suzan-Monti, 2006). Roughly 90% of the genome was of coding capacity, with the other 10% being “junk DNA”.