A basic virus is composed of a genome, capsid and viral envelope. Viruses are acellular, non-living organisms. They are classified as obligate intracellular parasites, which require a host organism to function.
The genome of a virus is all of its genetic material. Viruses can either have DNA-based genetic material or RNA-based genetic material. Their nucleic acids can be single or double stranded.
Viruses also contain capsids, which are proteins that coat and protect the nucleic acids within the virus. Some viruses contain outer viral envelopes composed of lipids, carbohydrates and proteins to protect the entire virion. The Influenza virus is an example of an envelope virus.