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Subject - Biochemistry, Immunology

Viruses are small, self-replicating nucleic acid/protein aggregates that depend on the metabolism of their host cell for replication. Viruses do not have their own metabolism; it is thus a question whether viruses can be considered a life form. The genome of a virus can be single- or double-stranded DNA or RNA. Viruses can have a very simple structure and may consist of only a nucleic acid with a protein shell (capsid) for protection. Some viruses pathogenic to animals have a more complex structure: their capsid is surrounded by a membrane made of lipids and glycoproteins that originates in the membrane of the host cell. Viruses that multiply in bacteria are called bacteriophages.

In humans, viruses cause many diseases, including measles, mumps, rubella, chicken pox, rabies, hepatitis, or influenza; some cancers are also related to viral infections (e.g. papilloma viruses). There are vaccines against some of these diseases; the use of antibiotics does not help against viruses.