"Domain" Virus

Viruses are nothing more than a segment of genetic material locked in a tiny shell. They have no cells, do not eat, and depend on host cells from other Domains to reproduce. As such, they pose many questions: How did they originate? How should they be classified? Are they even alive at all?

The genetic material in a virus can be RNA or DNA, can be one strand or two (like a latter), and copied (transcribed) in either a 'positive' or a 'negative' direction. The 'shell' (capsid) is a protein capsule built by the virus' genetic material. It can be spherical or helical/tubular.

All viruses reproduce the same way. They attach to a cell of one the other Domains. They inject their genetic material into it (or allow themselves to be engulfed). The 'hijacked' host cell then inadvertently copies (transcribes) the virus' genetic segment the same way it transcribes its own genetic DNA/RNA code. The host cell produces numerous copies of the virus, which rupture the cell and spread out to infect other cells.

All viruses are parasites; many are pathogens. They infect almost every living thing on earth. They have killed hundreds of millions of humans in the past and continue causing disease today. Viruses cause the common cold, smallpox, AIDS, herpes, Ebola, and many others. They are linked to other illnesses also.

Nevertheless, viruses are crucial to modern molecular and cellular biology. They are simple 'tools' that researchers use to penetrate, investigate, and manipulate the genetic code of cells. Viruses have allowed us to discover invaluable information about the cells of living things.