What about the invaded cell?

Bernard Bartfeld bab at gwis2.circ.gwu.edu
Sun Jan 14 02:38:47 EST 1996


Harry Boswell (hboswell at netdoor.com) wrote:
: I'm not a virologist, biologist, whatever - I'm a computer scientist who's
: married to a HS biology teacher, and I asked her a question she couldn't
: answer, so I thought I'd throw it out here.  My understanding is that a virus
: attacks by entering a cell and inserting DNA/RNA into the cell's chromosone
: structure, causing the cell to produce copies of the virus. (Sorry if I've
: oversimplified).  If so, what happens to the original cell?  Is it still
: the original cell type?  Has it itself become a viral cell?  Or with it's
: now-altered DNA, is it something else entirely?  

: Or, do I have this all wrong?

: Thanks for any info,
: Harry

: --
: Harry Boswell                 hboswell at netdoor.com  
: Home Page:  http://www2.netdoor.com/~hboswell

	Harry, I've only got a B.A. in Molecular Cell Biology, and we
studied only one virus's "life" cycle for a few weeks and discussed a few
variations, but here's my answer: Some viruses do insert themselves into
the DNA sequence of the infected cell.  The virus may remain dormant for
many years while the cell goes about its normal business.  Some viruses
don't invade the DNA sequence of the cell but remain in the cell as a
separate minichromosome.  In either case, the virus may produce viral
particles without killing the cell.  These viral particles can then escape
from the cell and infect neighboring cells.  This is done utilizing the
cell's inner workings, and may not be very harmful to the cell.  If the
cell replicates it may replicate the virus right along with the cell's
normal DNA.  This is scenario one.
	In scenario two, the very same virus may then suddenly enter a
different "life" cycle.  (Other types of virus only use this second
cycle.) This cycle is deadly to the cell.  The virus completely takes over
the cell's inner workings to make more and more viral particles much
faster than they can escape through the cell membrane.  At some point the
cell, jam-packed with viral particles, explodes, spreading the virus
throughout the immediate environment.  This second cycle has been 
theorized to occur when an infected cell is placed under other stress.
	As to what becomes of the cell, or what you call the cell when it
has the virus in it, I think there is a misunderstanding here.  Just
because a virus inserts itself into the genetic code of a cell, that
doesn't make the cell a new life-form.  Compare to when you catch a cold. 
There you are, a human being, but you and many of your cells are being
used as a cold virus factory.  The virus is using your internal workings
to make and spread the cold virus.  However, you remain a human being and
your sinus's cells remain human sinus (human epithelial?) cells.  Perhaps
you could say that you are a human being with a cold and that your cells
are infected with a cold virus, but you wouldn't say that you a viral
human nor that your cells are viral cells.
	I believe there is a name for the *virus* in its nonvirulent form
(scenario one): "prophage." 

	Note: "Life," above, is in quotes because viruses are said not to
be alive.  To me, that's arbitrary line-drawing, but it's also a different
discussion. 




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