Exceptions of living things NOT composed of cells?

Larry D. Farrell farrlarr at isu.edu
Mon Jan 26 14:00:00 EST 2004

Scott Coutts wrote:

> Tom Williams wrote:
> > I'm an undergraduate student who's curious about
>  > something mentioned in an anatomy lecture:
> >
> > My professor said that it was possible to have
>  > life without a cell, or cells.
> >
> > How can this be??? Can somebody please explain
>  > how, or even if this is true?
> >
> Hi Tom,
> It depends on how he defines 'life'. This always instigates a big
> discussion on what 'life' actually means.
> He's probably talking about anything able to replicate, so then he's
> including viruses. Viruses are able to replicate, but as far as I'm
> concerned, this is not 'life'... I dont regard viruses as 'living'. If
> you're interested, you might like to look up viriods and prions -
> they're able to replicate, but they're smaller than viruses... They're
> single molecules!
> Scott.

However, none of these are capable of replicating independtly of other
organisms, which is pretty much a requirement for "life" as it is
generally defined.  (Note, of course, that most eukaryotes need another
organism in the form of a mate to initiate the process of replication but,
once begun, the process does not depend specifically on the other organism
providing on-going functions for the process to continue to completion.)
Viruses and viroids are essentially inert unless placed into (or at least
in very close proximity to) host cells that provide the essential
functions and materials needed for replication, while prions produce
copies of themselves only if provided with properly folded copies of the
prion protein, usually provided by living host cells.

Larry D. Farrell, Ph.D.
Professor of Microbiology
Idaho State University

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