Download Virus Power Point

What is a Virus?
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Viruses are strands
of DNA or RNA
inside a protective
coat.
They cannot live on
their own, but
invade cells in your
body and use them
as factories to make
more viruses.
What is a Virus?
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This eventually kills
the cell.
Diseases caused by
the viruses includes
colds, flu and AIDS.
Properties of Viruses
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Viruses continue to mystify scientists.
They are so small and simple, that they do not fit the living cell
classification.
They range in size from 0.01µm to 0.3 µm in diameter.
Viruses have been found to produce diseases or genetic changes
in animals, plants, algae, fungi, protozoa and bacterial cells.
Properties of Viruses continued
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Viruses have 5 properties that separate them from living
cells:
1. They have DNA or RNA - never both.
2. Replication is controlled by the viral DNA in the host cell.
3. They do not divide by binary fission or mitosis.
4. Not capable of producing their own energy because they
lack the required genes.
Properties of Viruses
continued
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5. They depend upon the ribosomes and nutrients of infected
cells for protein production.
Viral Structure
Protective coat
of fats
and polysaccharides
Protein
Coat
DNA or RNA
not both
Invasion of the Host Cell
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This is a cyclic process.
1. Virus contacts host cell.
2. Virus or DNA enters host
cell.
3. Host cell DNA is broken up
and new viral DNA or RNA is
produced.
4. Viruses use protein from
host cell membranes to make
new protein coats.
Invasion of the Host Cell con’t.
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5. Viral enzymes are produced
that lyse the host cells.
6. Host cell membrane breaks.
7. New viruses are released.
Bacteriophages
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These are viruses that invade
bacterial cells.
Infective cycle is the same as
previous description.
In some cases the viral and
bacterial cell DNA join to form a
complex.
The subsequent daughter cells
will contain both DNA types.
Bacteriophage Animation