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Bacteria and Viruses?

Ed Rybicki ED at MOLBIOL.UCT.AC.ZA
Tue Sep 10 00:43:32 EST 1996


> From:          arthurc at crl.com (Arthur Chandler)
> Subject:       Bacteria and Viruses?

>  A question from a non-biologist (who has been reading Stephen Gould's 
> new book, *Full House*). Gould asserts (page 170):
> 
>   "...bacteria lie right next to the left wall of minimal conceivable 
> complexity. Life therefore began with a bacterial mode."
> 
>  1) Are viruses more or less complex than bacteria?
>  2) Are viruses alive?

Yes...B-)...and Yes and no...but both need qualification.  The largest 
viruses have genomes that are very nearly as large (+300 kb) as the 
genomes of the smallest cells (eg: mycoplasma, +500 kb); it is no 
coincidence that both are parasites.  In terms of "genome complexity" 
one could say that viruses GENERALLY are less complex than cellular 
organisms, but not necessarily so.  They are all obligate parasites, 
they lack ribosomes and the machinery of metabolism; however, they 
can order the cell's machinery to their needs, and some - like 
poxviruses, phycodnaviruses, and herpesviruses - have highly 
complicated genome expression strategies.

As for being alive: yes, viruses in a cell, actively replicating, are 
engaging in processes indistinguishable from those of a cell going 
about its normal business - and a cell is most certainly alive if it 
is metabolising.  However, once the viral genome is encapsidated, it 
is effectively a quiescent collection of large molecules - much like 
purified ribosomes - and, as it does not engage in any of the 
activities associated with living organisms, cannot be termed so.  
Mind you, neither can a bacterial spore that has been lying around in 
a dessicator for 50 or so years.  The point is that both a virion - 
the particle containing a viral genome - and a spore have the 
POTENTIAL for life, given the appropriate substrate.  Which is 
nutrients int he case of a spore, and a cell in the case of a virion.

Hope that clears things up a bit B-)

                     Ed Rybicki, PhD  
      Dept Microbiology     |   ed at molbiol.uct.ac.za   
   University of Cape Town  | rybicki at uctvms.uct.ac.za
   Private Bag, Rondebosch  |  phone: x27-21-650-3265
      7700, South Africa    |   fax: x27-21-689 7573
    WWW URL: http://www.uct.ac.za/microbiology/ed.html      
                                        
    "Out here on the perimeter, there are no stars..."



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