Key Terms
Virus
Acellular, obligate intracellular parasite. Not classified in the three domains of life.
Virion
The complete, mature viral particle outside a host cell.
Chamberland filter pore size
0.1 µm. Bacteria are ≥0.2 µm.
Size range
20 nm (small viruses) to 900 nm (large viruses). Giant viruses such as Pandoravirus salinus and Pithovirus sibericum app
Host range
Narrow or broad. Citrus tristeza virus: infects only a few Citrus genus plants.
Bacteriophages (phages)
Viruses that infect bacteria. Name from Greek for "devour."
Tissue tropism
Specificity for certain cell types within a host.
Example
Subterranean clover mottle virus (Sobemovirus) — has an associated virusoid packaged inside its capsid.
Mechanical transmission
Arthropod carries the virus on its body surface; transmits by physical contact. Biological transmission: arthropod carri
Common arthropod vectors
Mosquitoes, ticks, flies.
Zoonosis
Virus originates in an animal and is transmitted to humans.
Capsid
The protein coat surrounding the viral genome. Made of protein subunits called capsomeres (one or more types).
Naked (nonenveloped) virus
Nucleic acid + capsid only. No lipid layer.
Enveloped virus
Nucleic acid + capsid + phospholipid membrane (the envelope). The envelope is a portion of phospholipid membrane acquire
Spikes
Protein structures extending outward from the capsid (naked) or envelope. Allow attachment to host cells or assist in re