Bacteriophage T4 Virus
Viruses straddle the definition of life. They lie somewhere between supra molecular complexes and very simple biological entities. Viruses contain some of the structures and exhibit some of the activities that are common to organic life, but they are missing many of the others. In general, viruses are entirely composed of a single strand of genetic information encased within a protein capsule. Viruses lack most of the internal structure and machinery which characterize 'life', including the biosynthetic machinery that is necessary for reproduction. In order for a virus to replicate it must infect a suitable host cell.
Viruses exist in two distinct states. When not in contact with a host cell, the virus remains entirely dormant. During this time there are no internal biological activities occurring within the virus, and in essence the virus is no more than a static organic particle. In this simple, clearly non-living state viruses are referred to as 'virions'. Virions can remain in this dormant state for extended periods of time, waiting patiently to come into contact with the appropriate host. When the virion comes into contact with the appropriate host, it becomes active and is then referred to as a virus. It now displays properties typified by living organisms, such as reacting to its environment and directing its efforts toward self-replication.
A bacteriophage is a virus which infects bacteria. In particular, the bacteriophage T4 is a virus which infects E.Coli, a bacteria that has been used extensively for molecular biology research. The bacteriophage T4 exemplifies the life cycle of viruses. It exists as an inactive virion until one of its extended 'legs' comes into contact with the surface of an E. Coli. Sensors on the ends of its 'legs' recognize binding sites on the surface of the host's cell, and this triggers the bacteriophage into action. The bacteriophage binds to the surface of the host, punctures the cell with its injection tube, and then injects its own genetic blueprint. This genetic information subverts the host cell's normal operation and sets the cell's biosynthetic machinery to work creating replicas of the virus. These newly created viruses escape from the cell and then float about dormant until one happens to come into contact with a new host cell.
In nature, the bacteriophage T4 contains about 168,800 base pairs of double stranded DNA. This genetic blueprint contains all of the necessary information to create new bacteriophage T4. Our virtual bacteriophage T4 also contains its own genetic information; it is made up of characters of ascii VRML 2.0 code. At some point in the future evolution of cyberspace, our virus will find an appropriate host and replicate itself. The virtual virus is born, and the question of whether viruses are 'alive' is extended to the question of whether virtual viruses are alive!