Exceptions of living things NOT composed of cells?

Scott Coutts scott.coutts at med.monash.edu.au
Mon Jan 26 21:30:03 EST 2004

Larry D. Farrell wrote:

> 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!
> 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

Yep, I completely agree, but many still regard viruses, at least, as 
forms of life. That's why I mentioned the prion/viroid topic for Tom to 
read up on - because viruses require a host to replicate them, are they 
still definied as 'life'? And if so, surely viroids and prions must be 
counted too. I dont regard any of them as 'living'.

What about Rickettsias, Chalmydias and other obligate intracellular 
parasites, which cant synthesise their own ATP?


More information about the Microbio mailing list