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Biologist ___________________________
Date ______________
Viruses 20-1
Discovery of Viruses
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Ivanovski (1892) found the tobacco mosaic disease was found in __________ from
infected plants.
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Beijernick (1897) found small particles in this __________ and named them ________.
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Stanley (1935) isolated __________ of tobacco mosaic virus. Inferred viruses were not
truly __________.
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A __________ is a nonliving particle made of proteins, nucleic acids, and sometimes
lipids.
Structure and Composition
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Viruses are very small. Simple viruses contain only a _______ genes whereas the most
__________ may have more than a 100 genes.
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The protein coat surrounding a virus is called a __________.
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Most viruses have proteins on their surface membrane or capsid that bind to
receptor proteins on the __________ cell.
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The __________ “trick” the cell to take the virus, or in some cases just its genetic
material, into the cell.
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Inside the cell, viral genes are __________ and may __________ the cell.
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Most viruses infect only a very __________ kind of cell.
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Plant viruses infect plant cells; most animal viruses infect only certain related species
of animals; viruses that infect bacteria are called _____________________.
Viral Infections
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Inside living cells, viruses use their __________ information to make multiple copies of
themselves. Some viruses replicate __________, while others initially persist in an
__________ state within the host.
Lytic Infections
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In a __________ infection, a virus enters a bacterial cell, makes copies of itself and
causes the cell to burst, or lyse.
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The virus enters the cell and __________ reproduces and hijacks the cell to make
copies of the cell till it bursts (lyses).
Lysogenic Infection
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An infection where a host cell is not immediately taken over is a __________ infection.
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__________ is a bacteriophage’s DNA that becomes imbedded in the host’s DNA.
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The viral DNA becomes embedded in the host and inactive until a __________
(radiation, heat, chemicals, etc.) and it then becomes active.
A closer look at 2 RNA viruses
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In humans, RNA viruses cause a __________ range of infections, form relatively mild
colds to severe cases of HIV.
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About_______ of viruses contain RNA rather than DNA.
The Common Cold
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__________ is engulfed inside a cell where viral proteins make new copies of viral RNA
and in roughly 8 hours bursts the host cell.
HIV
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HIV is a __________.
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A __________ is one that is copied from RNA to DNA instead of DNA to RNA.
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First it makes a viral DNA copy of its RNA which inserts into the _______ of the host.
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It can remain __________, but once activated it will begin to destroy all body systems
used to fight __________
Viruses and Cells
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All viruses are __________.
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Viruses are NOT living because they don’t grow and develop, use __________ or
respond to the environment.
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BUT viruses do have structure, reproduce using a host cell, have _______________ and
change over time.