The copying process by which a cell duplicates its DNA?
Well a virus can duplicate many copies of itself by attaching itself to a cell, any cell, and using the cells machinery they inject their DNA and later the cell bursts and copies of the virus come out. When a bacteria duplicates it uses binary fission. Binary fission is when a bacteria splits itself into two and makes to copies of itself. Hope I answered your question.
When cells duplicate, DNA tells how the cell should react with its environment and how it should be constructed. for example when a person comes down with AIDS the AIDS (or HIV) virus messes with the DNA and so when the cell duplicates through mitosis it duplicates another cell with AIDS. Spreading it around the body