Viruses: non-living or alive?
A virus makes use of existing enzymes and other molecules of a host cell to create more virus particles. Viruses are neither unicellular nor multicellular organisms; they are somewhere between being living and non-living. Viruses have genes and show inheritance, but are reliant on host cells to produce new generations of viruses. Many viruses have similarities to complex molecules. Like DNA, viruses undergo molecular replication and they can often be crystallized. Because viruses are dependent on host cells for their replication they are generally not classified as "living". Whether or not they are "alive", they are obligate parasites, and have no form which can reproduce independently of their host. Like most parasites, they have a specific host range, sometimes specific to one species (or even limited cell types of one species) and sometimes more general.
Viruses form when molecules are assembled from organic compounds providing complex, microscopic structures which have the potential for self-assembly, and thusly they have large implications in the study of the origin of life. In the debate of whether viruses are alive or not, if the requirement for autonomous self-reproduction is abandoned, it can be strongly argued that viruses are indeed alive. Some small viruses are more efficient than most cellular life forms as their ratio of functions to working parts is so high. If viruses are alive then the prospect of creating artificial life is enhanced or at least the standards required to call something artificially alive are reduced.
