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Viruses
The “tiny” guys.
Wendell Stanley
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First isolated virus in 1933, the purified extract
crystallized.
Worked with the Tobacco Mosaic Virus.
Affects members of the tobacco family: white
potatoes, tomatoes and garden peppers.
Coined the term “virus,” it means “poison”
The Basics
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All organisms on Earth
have at least one virus
that affects them.
Viruses carry a piece of
DNA or RNA from a living
organism.
Pathogens: agents of
disease. “that which
produces suffering”
Viruses are not
considered to be alive.
The basics continued.
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Most viruses consist of DNA and a protein coat
called a capsid. This is used to bind the virus to
the host cell. Some have RNA and are called
retroviruses.
Viral Basics
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Many animal viruses
also have a membrane,
called an envelope, that
they took from the last
host as they were
pushing out of the cell.
It can be made from
proteins, lipids, and
glycoproteins. This
allows them access to
the new hosts cells.
Size
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Viruses range
between 20 and 200
nanometers.
They are barely able
to be seen with our
best light microscope.
Most are seen
through the use of
electron microscopes.
(TEM and SEM)
Shapes
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Helical shaped like the
Tobacco Mosaic Virus.
Polyhedral like the
adenovirus which
causes the common
cold
Shapes
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Round like the
influenza virus.
Complicated injection
structures like the
T4 bacteriophage,
“Bacteria eaters”
Reproduction
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No metabolic enzymes
No ribosomes, therefore, no equipment for
protein synthesis.
MUST have a living cell to carry out their
life cycle. “Hijackers”
Overwrites the cell blueprints, causes host
cells to become “Virus Factory”
Entry methods
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Bacteriophage punches hole in bacteria
and injects DNA.
Plant viruses enter through tiny holes/rips
in the cell wall. Holes/rips usually due to
injury to plant.
Animal viruses enter through endocytosis.
Cell is tricked into taking virus inside.
Animal virus specifics
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Very specific binding sites, like an enzyme
lock and key system.
Only receptor sites that exactly match the
virus glycoproteins will allow virus in:
HIV…white blood cells
Polio…spinal nerve cells
Hepatitis…liver cells
Meningitis…meninges of spinal column and brain
cells
Plant virus specifics
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Most plant viruses carry RNA, rather than DNA.
Some are carried by insects that feed on the
plants using piercing mouthparts.
Can cause severe damage to major cash crops.
Impatiens Necrotic Spot Virus (INSV)
Cucumber Mosaic Virus (CMV)
Tomato Ringspot Virus (Tom RSV)
Viral Origins
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Fragments of host genomes.
Incredible diversity due to so many templates
available to escape from.
Coevolutionary partnership offers protection to
species habitats.
Viruses of nearly all the major classes of
organisms - animals, plants, fungi and
bacteria / archaea - probably evolved with
their hosts in the seas, given that most of
the evolution of life on this planet has
occurred there.