Viruses

When is a life form not a life form? When it's a virus.
Viruses are strange things that straddle the fence between living and non-living. On the one hand, if they're floating around in the air or sitting on a doorknob, they're inert. They're about as alive as a rock. But if they come into contact with a suitable plant, animal or bacterial cell, they spring into action. They infect and take over the cell like pirates hijacking a ship,
A virus is basically a tiny bundle of genetic material either DNA or RNA carried in a shell called the viral coat, or capsid, which is made up of bits of protein called capsomeres. Some viruses have an additional layer around this coat called an envelope. That's basically all there is to viruses.
When viruses come into contact with host cells, they trigger the cells to engulf them, or fuse themselves to the cell membrane so they can release their DNA into the cell.
Once inside a host cell, viruses take over its machinery to reproduce. Viruses override the host cell’s normal functioning with their own set of instructions that shut down production of host proteins and direct the cell to produce viral proteins to make new virus particles.
Some viruses insert their genetic material into the host cell’s DNA, where they begin directing the copying of their genes or simply lie dormant for years or a lifetime. Either way, the host cell does all the actual work: the viruses simply provide the instructions.
Viruses may be able to