Re-Is a virus alive?

GS microHero at compuserve.com
Wed Feb 5 00:55:22 EST 1997


Steven Projan wrote:
> 
> This is a frequently asked question and debated issue.  Just because
> virus are parasites requiring a host cell in which to replicate does
> not make them non-living as there are many examples for bacteria
> (which most of us would consider alive) which are obligate
> intracellualr pathogens.  But if we consider viruses as living
> entities than where do we draw the line?  What about plasmids, which
> are composed solely of DNA and replicate inside cells (usually
> bacteria) but do not become encapsidated live viruses?  In 1980
> Richard Novick wrote an article for Scientific American in which he
> referred to plasmids as the smallest of organisms.  If we accept
> plasmids as organisms then where do we put prions?   And what about
> those degenerate bacteria, the mitochondria and cholorplasts, do we
> consider these the formerly living, the undead, really nice
> parasites, symbionts?
> 
> Perhaps we should just consider that there is a continuum between
> what is the biochemical and what is the living.  Perhaps life is like
> pornography - I believe it was Supreme Court Justice Hugo Black who
> said that he don't know how to define pornography but he knew it when
> he saw it.
> 
> Steve Projan
> Wyeth-Ayerst Research

But you can't define what you don't delimit - if there is a chemical 
process or set of processes which can be identified as "life" there must 
be distinguishing characteristics. If life is simply the ability to 
replicate macromolecular structures from a pre-existing template then 
crystals are alive. Since one essential characteristic of life is a local 
entropy reduction crystallisation should qualify. Some theories of prion 
formation are not really that far from this idea.

Personally I go for a definition which includes the presence of nucleic 
acid (RNA, DNA or both). You still have a problem - is a 'flu virus an 
organism or a community? Ditto for diploid and polyploid cells...

Graham Shepherd
microHero at compuserve.com



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