Viruses are not cells. They do not have a nucleus or other organelles that are associated with cells. They have no metabolism and are considered genetic parasites in that they use the host cell for but one purpose---to replicate their genetic material and produce progeny virions (infectious viral particles). The effect on the host cell, which can range from no effect, to a disruption in cellular function, to killing of the host cell, is related to the disease state caused by the infecting virus.The structural organization and morphology of viruses vary. Basically they are composed of a protein, called the capsid, that surrounds their genetic material---nucleic acid of either DNA or RNA. Together this structure is called the nucleocapsid. In addition, some viruses have an outermost covering called the envelop that is added to the virus as the virus buds from the host cell. Thus, this structure is of host cell origin. The lipid composition of this envelop is identical to the host cell membrane; it may carry some of the host cell membrane proteins as well. The virus can add its' own proteins to this envelop. An example of such an enveloped virus is HIV. The size of animal viruses range from a diameter of approximately 20 nanometers (nm = 10- 9 meters) for Parvoviruses to approximately 200nm for Poxviruses. The diameter of animal cell is approximately 0.01mm (millimeter= 10 - 3 meters). The highest taxonomic grouping for viruses is the Family with subdivision into subfamilies, genera, species, and strains or serotypes. Related Topics |
