Download Viruses Virus • Microscopic particle that invades and

V iruses
Virus
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Microscopic particle that invades and kills a cell
Smaller than bacteria
Change rapidly
Cannot perform all life processes
Can only reproduce in a host cell
o Host – organism invaded by a parasite
Classifying Viruses
 All viruses contain nucleic acid (either DNA or RNA) surrounded by a protein
coat
 Classified by shape
o Crystals
o Spheres
o Cylinders
o Spacecraft
Cycles of viruses
 Lysogenic Cycle – the virus goes into a host cell but remains inactive; when the
host cell divides, copies of the viruses genetic material will go into each new cell;
when the virus becomes active, it begins the lytic cycle
 Lytic Cycle
o Virus attaches itself to the host cell
o The virus injects its genetic material into the host cell
o The genetic material takes over the host cell and instructs the cell to make
new virus parts
o The virus parts join to make new viruses which burst out of the host,
killing the host cell.
o The cycle begins again
Fighting a Virus
 Vaccines can be given to prevent viruses
o Inject a small amount of dead or weakened virus
o Body will form antibodies that kill that particular virus
o If you come in contact with the virus, your body will remember it and
make additional antibodies so that you can quickly kill off the virus
 Antiviral Drugs
o Some drugs can prevent a virus from reproducing