Viruses Viruses Return to Scientific Viruses can only reproduce in living cells. They invade the cell and take over its biochemical systems to make more virus. The virus DNA switches on the cell's DNA to make only more virus DNA and virus proteins. Some viruses incorporate their DNA permanently in the cell's DNA and can remain quiescent for many years. Human cells have viral DNA incorporated in the human DNA, the invasion taking place many thousand or millions of years ago.
Bacteriophages are viruses that invade Bacteria and reproduce there, usually killing the bacteria.
Researchers are looking for bacteriophages that will kill bacteria but leave human cells alone. The HIV virus infecting humans can produce over a million different mutants each 24 hours, and so some will overcome the hosts immune systems and also produce drug resistant HIV strains. These resistant strains will then rapidly reproduce in the host. The viral coat of protein differs from the bacterial cell wall. Antibiotics attack the bacterial cell wall and stop bacteria from growing and reproducing.