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Viruses; Genisis and Taxonomy

Giovanni Maga maga at vetbio.unizh.ch
Fri Jan 19 02:27:36 EST 1996

In article <DLEu8n.EJB at watserv3.uwaterloo.ca>, Craig Kuchocki *Spidey*
<CJKUCHOC at SCIENCE.Watstar.UWaterloo.CA> wrote:

> The virus is a free entity until it infects a host.  I was correcting a 
> professor last week when she called viruses "organisms" but I failed to 
> come up with a suitable term to refer to them by.  Calling them organisms 
> is just for lack of better terminology.  When a virus has infected an 
> organism and is replicating, it can be considered alive and is classified 
> as an organism.

I do not agree with this one. I do not want to re-open the debate about
viruses considered as living, but since the virus is an entitity with well
distiguishable characteristics and its own taxonomy, IF you consider it a
living organism, THEN you should do it regardeless the point of its life
cycle you are looking at. 
Along your line, we should then consider any kind of parasite that needs
to be within a host cell to replicate as non-living, non-organism until it
is effectively replicating (think about protozoal parasites that have
resistance forms like oocysts to survive outside the host). If then we CAN
consider a virus as an organism is another matter. I think it strictly
depends on how we define both organisms and life and I believe it is more
a semantic problem than a real one.

> Viruses replicate using the machinery in the host organism.  All the 
> components of the progeny are assembled by the host cell (ie. the DNA/RNA 
> and amino acids).  They cheat their way through a life cycle in a way.

It is not entirely correct. Many viruses replicate their DNA/RNA genome by
virtue of viral enzymes (DNA polymerases, Reverse Transcriptase). Some of
them also have enzymes and proteins essential for transcription of their
own genes. Of course nucleotides and aminoacids are taken from the cell,
but, for example, herpes viruses also have basically all the essential
enzymes not only for replication (helicase/primase, DNA polymerase etc.)
but also enzymes for nucleotide biosynthesis (thymidine/deoxycytidine
kinase, thymidylate kinase).

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