Viruse
Viruse are non-cellular infectious agents that depend on host cells to replicate. They range in size from about 20 to 300 nanometers and contain genetic material—DNA or RNA—enclosed in a protein coat called a capsid. Some viruse also have a lipid envelope derived from the host cell membrane. Inside the host, viruse direct the cell's machinery to produce viral components, often disrupting normal cell function.
Viruse are classified by genome type (DNA or RNA), strandedness (single or double), symmetry of the capsid,
Life cycle: attachment to a suitable host receptor, entry by endocytosis or membrane fusion, genome release,
Host range varies widely—viruse can infect animals, plants, fungi, or bacteria (bacteriophages). Transmission routes include respiratory
History: the existence of viruse was established in the late 19th and early 20th centuries with work