Viruksen

Viruses are submicroscopic infectious agents that replicate only inside living cells. They are not considered living organisms by many definitions because they lack metabolism and cellular organization outside a host. A virus particle, or virion, contains genetic material—DNA or RNA—encased in a protein coat called a capsid; some viruses also have a lipid envelope.

Viruses vary in size and shape, from 20 to several hundred nanometers, and in genome organization, which can be single- or double-stranded, and linear or segmented. They infect all forms of life, including bacteria, plants, and animals.

Replication occurs by hijacking the host cell’s machinery. After binding to a receptor, the virus enters or injects its genome, uses host and viral enzymes to replicate, and produces new viral proteins. Assembled virions are released by cell lysis or budding, often causing cell damage or death. Some infections are acute and self-limiting, others establish latency or chronic replication.

Classification systems group viruses by genome type and replication strategy (the Baltimore system) and by structure and family names (e.g., Herpesviridae, Retroviridae). In medicine, viruses are targets for vaccines and antiviral drugs, and they are widely used as tools in biotechnology, such as viral vectors for gene delivery.

Public health surveillance, hygiene, vaccination, and antiviral therapies help reduce viral diseases. Ongoing research explores virus evolution, host interaction, and how viruses adapt to new environments and hosts.