Virus
The Papillomavirus is a DNA virus
that causes warts. These infectious
particles are small, about 15 nm in
diameter
The Adenovirus is a DNA virus that
causes colds and "pink eye".
Viral diseases in humans
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AIDS
Chicken pox
Common cold
Influenza
Measles
Mumps
Polio
immune system
skin
Respiratory system
respiratory system
skin
Salivary Tissue
Nervous System
Definition
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A virus is a small infectious piece of
material— much smaller than a
fungus or bacterium—that must
invade a living cell to reproduce
(replicate).
Adenovirus
The polio virus, left, once crippled millions.
Courtesy of the MicrobeLibrary.org; © Jean-Yves
Sgro, University of Wisconsin. The T4
bacteriophage, middle, is a virus that invades
bacterial cells. Courtesy of the
MicrobeLibrary.org; © Dennis Kunkel. Gold
clusters bound to the knob protein of Adenovirus,
right. Courtesy of Brookhaven National
Laboratory.
Virus Basics
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not living but contain genetic
material
lack all cell structures
can reproduce ONLY in living cells
and do not carry out any other life
processes.
they survive by using the cell’s
“machinery” to reproduce
More basics
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the Latin word for
poison is virus
1892 a Russian
biologist
discovered the first
virus (a plant
virus)
has genetic
material (DNA or
RNA) wrapped in a
protein coat
tobacco mosaic virus
What is a bacteriophage?
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It is a bacteria “eater”
Since the invention of the electron
microscope, it is known as a virus.
(we’ll use microviewers in class)
Size of common viruses
Name
Size
Cowpox and smallpox 250 nm
Influenza, mumps
100 nm
Tobacco mosaic virus 65 nm
Yellow fever virus
22 nm
Polio
12 nm
Nanometer to meter
{scientific notation}
Size
250 nm
Conversion
250 x 10-9
100 nm
x 10-9
65 nm
x 10-9
22 nm
x 10-9
12 nm
x 10-9
How do viruses infect cells ?
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The virus takes control of the cell
machinery
The cell “forgets” its own needs and
works for the benefit of the virus.
There are 4 steps to how a virus
duplicates itself once it attaches to a
cell :
1
2
3
4
More on Active Viruses
Attach
a specific virus attaches to the surface of
specific bacterial cell.
Invade
The genetic material of the virus is injected into the
host cell
Copy
The nucleus of the host cell begins copying the
genetic
material of the virus
Release
The cell bursts and a lot of new viruses are
released. The
new virus cells go on to infect other cells.