The smallest life forms known, that are not cellular in nature. They live inside the cells of animals, plants and bacteria and often cause disease. They are made up of a chromosome surrounded by a protein shell. The properties of viruses are its features that make up its characteristics. Viruses have a nucleic acid that consists of RNA or DNA, and are categorized as both non-living and living matters. Viruses play a non-active role when exiting from outside of host cells, however become active when inside of the host cells.