last authored: Dec 2009, David LaPierre


H1N1 influenza virus, CDC


Viruses are packages of genetic information contained by protein shells, designed for delivery into host cells for protein expression and replication. They have very small genomes made up of DNA or RNA, with most lacking a nuclear membrane or cell wall. Viruses are much smaller than bacteria, measuring 20-300 nm in diameter.


Their simplicity makes them obligate intracellular parasites, requiring host machinery for replication.






Specific Viruses


Virus Structure

A virus, or virion, contains a nucleocapsid - the genome plaus the protein capsid.

The genome may be DNA or RNA, and can be single-stranded, double-stranded, linear, circular, or segmented.

The capsid contains repeating capsomeres. These are usually helical or isocahedral, with 20 sides.

Some viruses only contain nucleocapsid, but others are covered by a large envelope, with inner proteins and outer lipids, with glycoproteins protruding through.

Structural proteins include the capsid, core nucleic acid packaging proteins, or envelope glycoproteins. Non-structural proteins include enzymes.



Viral transmission can occur in many ways. These include



Effects of Virus Infection

Viruses can cause:

Viruses can have many effects on cells.



Virus Replication



Virus Diagnosis