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The Amazing
World of Viruses
Viral History
2
Discovery of Viruses
•Beijerinck (1897)
coined the Latin
name “virus”
meaning poison
•He studied
filtered plant juices
& found they
caused healthy
plants to become
sick
3
Tobacco Mosaic Virus
•Wendell Stanley
(1935) crystallized
sap from sick tobacco
plants
•He discovered
viruses were made of
nucleic acid and
protein
4
Smallpox
•Edward Jenner (1796)
developed a smallpox
vaccine using milder
cowpox viruses
•Deadly viruses are
said to be virulent
•Smallpox has been
eradicated in the world
today
5
Viewing Viruses
•Viruses are smaller
than the smallest cell
•Measured in
nanometers
•Viruses couldn’t be
seen until the
electron microscope
was invented in the
20th century
6
Interdependence
Viruses and
organisms rely
on their
environment
and other
species for survival.
Viruses
But, Viruses are NOT cells.
A virus is an infectious agent made up
of:
•a core of nucleic acid (RNA or DNA)
•a protein coat
Alive or not?
Even scientists disagree as to
whether or not viruses are
alive. What do you think? Look
at the chart on the next page
to help you decide.
Characteristic
of life
CELL
VIRUS
Made of cells
YES
NO
Obtain & use
energy
YES
NO
Grow & develop
YES
Reproduce
YES
Respond &
adapt
Contain RNA or
DNA
Only inside a
living cell
Only inside a
living cell
YES
YES
YES
YES
Alive or not?
Most scientists do not consider
viruses to be living because don’t
have the necessary parts to
reproduce on their own.
They MUST infect a cell and use
its parts to reproduce.
Structure
of a virus
ENVELOPE
Because viruses don’t
carry around the
necessary parts to
reproduce
themselves they
are very simple
structures.
NUCLEIC
ACID
CAPSID
Structure
of a virus
Consists of 2 parts: ENVELOPE
1. A Nucleic acid either DNA or
RNA
2. Capsid – A protein
Coat that
surrounds and
NUCLEIC
protects the ACID
DNA/RNA
CAPSID
Types of Viruses
1. Standard DNA based Virus
2. Retro Virus
3. Bacteriophage
Basic Virus
A strand of nucleic acid surrounded
by a protein coat.
DNA  RNA  Protein
Retrovirus
A virus that
contains RNA
instead of DNA
ENVELOPE
RNA
Human
Immunodeficiency
Virus (HIV) is a
retrovirus
HIV causes AIDS
CAPSID
Bacteriophage
A virus that
infects only
bacteria.
CAPSID
HEAD
DNA
CAPSID
TAIL
FIBER
Helical Viruses
21
Polyhedral Viruses
22
Complex Viruses
23
24
Ticking time
bombs . . .
Viruses CANNOT reproduce,
EXCEPT inside a living cell. They
invade a living cell and let the cell
work for them.
Virus Cycle
A Viral Infection has 2 possible
stages:
1. Lytic Cycle
2. Lysogenic Cycle
*Some viruses go straight to the
lytic phase and never enter
the lysogenic phase
Virus Cycle
1. Lytic Cycle - stage where
virus is actively reproducing
and killing host cells
2. Lysogenic Cycle - stage where
virus is inactive and host cells
remain unharmed
1.
Lytic Cycle
The virus injects its DNA into the host
cell
2. The DNA uses the host cell’s resources
and organelles to make new viruses.
3. The viruses cause the cell to burst
4. The cell dies and the newly made copies
of the virus are released to go infect
new cells.
5. The cycle continues.
Cycle Illustration
1
2
4
3
5
Lysogenic Cycle
1.
The Virus injects its DNA into the host
cell.
2. The DNA inserts itself into the host cell’s
DNA and stays there inactive.
3. There are NO symptoms of the infection
at this stage.
4. Eventually the viral DNA will remove
itself from the host cell’s DNA and the
lytic cycle will begin.
Lytic
Cycle
LysoGenic
Cycle
Role of viruses
All viruses are parasites: they benefit while
harming the host cell/organism.
Viruses cause disease in every kind of
organism—animals, plants, fungi, protists,
and bacteria.
Viral diseases
Are hard to cure, but many
can be prevented by
•Good hygiene
•Immunization
Some viral diseases
•
•
•
•
•
HIV
Measles
Smallpox
Influenza
Chicken pox
•
•
•
•
•
Common cold
Herpes
Warts
Mononucleosis
Mumps
MEASLES
Mumps
SMALLPOX
HERPES
1918 Flu
Herpes Virus
SIMPLEX I and II
41
Adenovirus
COMMON COLD
42
Influenza Virus
43
Chickenpox Virus
44
Papillomavirus –
Warts!
45
Helical Viruses
46
Polyhedral Viruses
47
Complex Viruses
48
Links
http://www.virology.net/Big_Virology/BVFamilyIndex.html
Sources
http://www.virology.net/Big_Virology/BVFamilyIndex.html
Biology, Kenneth R. Miller & Joseph Levine, 1991, Prentice-Hall, Inc.,
Englewood Cliffs NJ.
Biology: The Web of Life, Eric Strauss & Marylin Lisowski, 1998,
Scott Foresman Addison Wesley, Menlo Park CA
TAKS Power Tools, Glencoe Science, Glencoe McGraw-Hill, 2001, New
York, NY.
Microsoft Office Clipart