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What is a virus

Paul Digard pd1 at mole.bio.cam.ac.uk
Thu Jun 5 03:34:22 EST 2003

> Is a virus a living organism or a biological machine?
> Thanks.
> Two Mechanical Engineers.

I don't think there's a definite answer to this: is a cell a biological 
machine?  There's also quite a large continuum of things that are 
defined as viruses (obligate intracellular parasites with an eclipse 
phase).  My favourite virus (flu) has a relatively small genome with 
only 10-11 genes and under the right circumstances it can limp along 
without at least 4 of these.  Quite simple diagrams can be drawn about 
how the proteins encoded by these genes interact with each other to make 
a new virus, as long as you're willing to ignore the host factors and 
don't mind a degree of plausible guesswork.  I've always thought of flu 
as a piece of biological clockwork and have no problem with classifying 
it as a non-living parasitic nanomachine.  There are simpler viruses out 
there too, even before you get down to the level of viroids and so on. 
But, on the other hand, there are viruses with genomes that are orders 
of magnitude larger than influenza's, including some that are comparable 
in size to, if not larger than those of the smallest known free living 
organisms.  Where do you draw the line?

Probably not much help!

Paul (a virologist)


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