Indeed, it was a chemical that could reproduce like it was alive, yet needed the cells of a host organism to do so, and could be crystalized, but remained viable and infectious even then. The smallest viruses are smaller than ribosomes in cells, and the largest are so big that they re just barely visible under the highest power of magnification possible with a regular light microscope. Virions can be separated into separate nucleic acid and protein components, each separately crystallized and stored, and yet if mixed back together, can reassemble and be just as viable , as infective, as before. Viruses are obligate intracellular parasites , that is, they can express their genes, do chemical synthesis of more viral nucleic acid and protein, and replicate only within a living cell of the correct host species. When a virus enters a host cell, it takes over the host cell s metabolic machinery and chemical pathways and uses these to make more virus protein and nucleic acid, which then spontaneously come together to form not two, but MANY new virions.
Viruses are capable of replicating many copies of themselves, which then go infect other cells.
However, each type of virus has a limited range of host cells. Viruses use a sort of chemical lock and key mechanism to join to receptor sites on the surface of their host cell, thus the host may be only one or or several closely-related species. Herpes viruses are especially known for this, and it is thought that some forms of cancer may be caused in this way. When these replicate, they then burst out of the host bacterium cell, killing it as many viruses are released. To infect a new cell, the membrane surrounding the virus joins with the cell membrane of a host cell, and the capsid and nucleic acid sneak inside.