A virus is mostly made of hereditary material (DNA or RNA) with a protein covering. It has no nucleus, no mitochondria, and few other parts that are usually found in a cell. Use the Cell Theory to explain whether a virus is alive or not. A virus is not alive, because each individual virus lives by itself. A virus is not alive, because it is not made of cells. A virus is alive, because new viruses come from existing viruses. A virus is alive, because it can attack animal cells, and use the animal cells to produce new viruses.