Viruses are sometimes regarded as the simplest known
living things although other people do not accept that they are living. This comes down to defining what living means
and there is no universally accepted definition.
The viruses that have been discovered so far have all
been parasites that enter a cell and change the cell’s instructions so it
produces copies of the original virus.
Free Living
Viruses
No free living viruses are known. However, if they existed, finding them would
be an extremely difficult job. With
disease causing viruses, their presence is suspected from their effects on the
host they are infecting. Even then
finding the virus is a difficult job.
However, if, for example, there were some free living
viruses in the ocean, the job of finding them would make finding a needle in a
haystack seem very easy.
But although no free living viruses have been found,
it is entirely possible that they do exist. Even if they do not exist, they may have existed in the past.
For a virus to be free living it would have to
replicate its nucleic acid from nucleotides, ribose sugars and phosphate
groups. Nowadays there is possibly no environment with
consistently enough of these. Having
replicated its nucleic acid the virus would then need to assemble its protein
sheath. However, the main use of the
protein sheath is to enter cells. So
perhaps a free living virus might consist of only self replicating nucleic
acid. This could be much simpler even
than the viruses that are known.
Of course someone might argue that this
hypothetical entity was not a virus. Again this is a matter of definition.
Where do
viruses come from?
We do not know how they originated and there are
several different theories. One of these
theories is implied by the previous paragraph. In the early seas and other water bodies of the Earth, there may have
been quite a lot of nucleic acids and other organic compounds including ribose
sugars and phosphate groups. Some
chemicals could form capable of using the simpler organic compounds to make
copies of themselves. This is what DNA
does. These self replicating chemicals
would not be what most people would call life. They would not always make perfect copies of themselves. Competition would develop between these self
replicating chemicals for the organic building blocks. The self replicating chemicals most efficient
at using them would make more copies of themselves. So these pieces of DNA would develop into
what we might call a free living virus.
This might have happened before there was any cellular
life. Perhaps when cells started to
appear some of the free living viruses started to enter the cells and were in
an ideal environment to self replicate. Maybe it was at this point that the protein sheath became an advantage
to enable the nucleic acid of the virus to be injected into the cell.
Antivirus
In recent times these parasitic type viruses have
become an important disease causing agent. Effective antivirus drugs are a quite recent development. The most important specific preventative for
viruses is still vaccination.
General
Health
Many common viruses such as the common cold cannot yet
be vaccinated against. A well balanced
diet containing enough fresh fruits and vegetables and other foods will ensure that our bodies have
the nutrients needed for our immune systems. Another factor is to avoid excessive stress. Someone who is stressed is more likely to get
ill.
Sources
History of virus: http://library.thinkquest.org/26802/origin.html
