Have nucleic acids to make copies of themselves, take over cell machinery Causes diseases in plants and animals, bacteria infected by bacteriophages or phages Colds, AIDS, rabies Russian botanist studying tobacco mosaic disease, passed sap through filters small enough to catch bacteria. Later another botanist said disease could only reptoduce in living cell, but had characteristics of living organism. A nucleic acid core surrounded by protein coat or capsid.
Some viruses also have membranous envelope of proteins, lipids, carbohydrates, trace metals.
Cannot do cellular respiration or synthesize proteins, etc Has either RNA or DNA, not both. All living organisms have both. Virus nucleic acid may have escaped from cells Species specific for the type of cell they came from. Genetic similarity between virus and host, more so than other viruses. Phages can be cultured in bacteria in lab, used in genetic engineering.