October 15, 2009
Are Viruses Alive?
A research into the puzzling world of viruses
Joshua Cerna
Science
How viruses were discovered
• About 111 years ago 2 scientists, Friedrich
Loeffler and Paul Frosch, discovered the
cause of a fatal disease in cows and sheep
called foot-and-mouth disease.
• This disease was caused by something
smaller than bacteria, something that had
strange properties. It was called a virus since
it was different from anything else known at
that time.
Viruses as virions in the air
• When viruses are outside of host cells they
appear dormant. In this dormant state they
are called “virions.”
• Virions appear to be non-living and are
metabollically inert. In this state they are
nothing more than static organic particles.
• Virions cannot move about on their own but
instead get carried around in the air when
animals and humans cough or sneeze.
Sample photo of virions
•
Below is a photo of virions of the H1N1 influenza virus
that causes the commonly called “swine flu” disease in
humans. It is currently spreading fast in North America.
Viruses inside host cells
• When virions in the air get breathed in by
other animals and humans, the virions attach
themselves to the host cells of the animals
and humans, and become active. In this
active state they are properly called “viruses.”
• Viruses appear to be living while inside their
host cells. For example, viruses react and
adapt to their environment within the host
cells. Viruses also replicate inside the host
cells.
Diagram of a virus infection
•
Below is a diagram of how a virus might infect a human.
Viruses replicating themselves
• Viruses by their own selves cannot reproduce
or replicate. Viruses use their host cells as
factories for replicating themselves.
• Viruses force the host cells to do their bidding
to replicate with chemical commands for
doing so.
• After replicating inside a host cell, viruses
break out of that host cell and go on to take
control of more host cells.
Virus evolution
• Viruses are made up of either RNA or DNA
genetic material. This genetic material easily
changes as the viruses react to their
environment. This is how viruses evolve.
• Viruses that cause diseases in different
animals often mix each other’s genetic
material and result in newer mutated forms of
viruses.
• The current H1N1 virus is actually a mutation
of viruses that originally came from birds
(avian), pigs (swine), and humans.
Diagram of a virus mutation
•
Below is a diagram of how a virus’ genetic material might
mutate within a host cell.
H1N1 virus evolution
•
Below is a diagram of how the H1N1 virus evolved from
previous avian, swine and human viruses.
So, are viruses alive?
• In a way viruses aren’t really alive because
they depend on a host cell to replicate.
• Also, viruses aren’t made up of cells like
those found in plants and animals. They
really are made up of just RNA or DNA
material surrounded by a protein shell. They
are so simple as to seem not alive.
• However, viruses can seem alive in their
replicating activity inside host cells. So my
opinion is neutral on whether or not viruses
are alive.
Viruses are unique
• Although viruses aren’t made up of cells and
might appear to be non-living, they possess
behavior consistent with being alive such as
when they replicate.
• One scientist said, tongue in cheek, that
“viruses are on borrowed life.”
• Because viruses sometimes appear dormant,
and viruses sometimes appear alive, I think
that viruses are unique and should be
classified separately from living organisms.