In an episode of the classic 1950s television comedy The Honeymooners,
Brooklyn bus driver Ralph Kramden loudly explains to his wife, Alice, “You know
that I know how easy you get the virus.” Half a century ago even regular folks
like the Kramdens had some knowledge of viruses—as microscopic bringers of
disease. Yet it is almost certain that they did not know exactly what a virus
was. They were, and are, not alone.
For about 100 years, the scientifi c community has repeatedly changed its
collective mind over what viruses are. First seen as poisons, then as
life-forms, then biological chemicals, viruses today are thought of as being in a gray
area between living and nonliving: they cannot replicate on their own but
can do so in truly living cells and can also affect the behavior of their hosts
profoundly. The categorization of viruses as nonliving during much of the
modern era of biological science has had an unintended consequence: it has led
most researchers to ignore viruses in the study of _evolution_
(http://www.sciam.com/topic.cfm?id=evolution) . Finally, however, scientists are beginning
to appreciate viruses as fundamental players in the history of life.
Coming to Terms
It is easy to see why viruses have been diffi cult to pigeonhole. They seem
to vary with each lens applied to examine them. The initial interest in
viruses stemmed from their association with diseases—the word “virus” has its
roots in the Latin term for “poison.” In the late 19th century researchers
realized that certain diseases, including rabies and foot-and-mouth, were caused
by particles that seemed to behave like _bacteria_
(http://www.sciam.com/topic.cfm?id=bacteria) but were much smaller. Because they were clearly
biological themselves and could be spread from one victim to another with obvious
biological effects, viruses were then thought to be the simplest of all living,
gene-bearing life-forms.
Their demotion to inert chemicals came after 1935, when Wendell M. Stanley
and his colleagues, at what is now the Rockefeller University in New York City,
crystallized a virus— tobacco mosaic virus—for the fi rst time. They saw
that it consisted of a package of complex biochemicals. But it lacked essential
systems necessary for metabolic functions, the biochemical activity of life.
Stanley shared the 1946 Nobel Prize— in chemistry, not in physiology or
medicine—for this work.
Further research by Stanley and others established that a virus consists of
nucleic acids (DNA or RNA) enclosed in a protein coat that may also shelter
viral proteins involved in infection. By that description, a virus seems more
like a chemistry set than an organism. But when a virus enters a cell (called
a host after infection), it is far from inactive. It sheds its coat, bares
its genes and induces the cell’s own replication machinery to reproduce the
intruder’s DNA or RNA and manufacture more viral protein based on the
instructions in the viral nucleic acid. The newly created viral bits assemble and,
voilà, more virus arises, which also may infect other cells.
These behaviors are what led many to think of viruses as existing at the
border between chemistry and life. More poetically, virologists Marc H. V. van
Regenmortel of the University of Strasbourg in France and Brian W. J. Mahy of
the Centers for Disease Control and Prevention have recently said that with
their dependence on host cells, viruses lead “a kind of borrowed life.”
Interestingly, even though biologists long favored the view that viruses were mere
boxes of chemicals, they took advantage of viral activity in host cells to
determine how nucleic acids code for proteins: indeed, modern _molecular
biology_ (http://www.sciam.com/topic.cfm?id=molecular-biology) rests on a
foundation of information gained through viruses.
**************Looking for a car that's sporty, fun and fits in your budget?
Read reviews on AOL Autos.
(http://autos.aol.com/cars-Volkswagen-Jetta-2009/expert-review?ncid=aolaut00030000000007 )
To unsubscribe/subscribe or view archives of postings, go to the Gambia-L Web interface
at: http://listserv.icors.org/archives/gambia-l.html
To Search in the Gambia-L archives, go to: http://listserv.icors.org/SCRIPTS/WA-ICORS.EXE?S1=gambia-l
To contact the List Management, please send an e-mail to:
[log in to unmask]
|