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Chapter 18.2 Viruses and Prions
“Viruses and prions are smaller and less
complex than bacteria;
they invade cells and can alter cellular
functions.”
Chapter 18.2 Learning Targets
• Illustrate the general structure of viruses.
• Compare and contrast the sequence of events in viral
replication by the lytic cycle, the lyosgenic cycle, and retroviral
replication.
• Discuss the structure, replication, and action of prions in
relationship to causing disease.
Characteristics
• non-living particles
• invade living cells
• pathogenic - named after
the disease they cause or
organ they infect
• smallest of all organisms
T-4 Virus - infects E. coli
VIRUS - an obligate intracellular
parasite
INFECTIOUS MONONUCLEOSIS
Origin of Viruses
• Viruses may have
originated from host cells
• 1935 - first seen by an
electron microscope
• Tobacco mosaic virus first virus discovered 1886
Wendell Stanley (1904 1971) first isolated TMV
in 1935.
1886 - “Living Fluid Infectant” - the
virus passed through filters that held
bacteria.
Viral Structure
• Inner core contains viral DNA
or RNA (never
both)
• Capsid - outer coat
of protein
• Envelope - outer
layer on larger
viruses
Various Shapes of Viruses
Viral Replication
Lytic Cycle
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1. Attachment
2. Injection
3. Replication
4. Assembly
5. Lysis
LYSOGENIC CYCLE
1. Attachment
2. Injection
3. Viral DNA
integration
(provirus)
4. Cell division
5. Replication
6. Assembly
7. Lysis
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Viruses
Bozeman Biology
http://www.youtube.com/watch?v=L
8oHs7G_syI
8:06 min.
VIRUSES
CHAPTER 18
Part 2
Edward Jenner discovered a vaccine for smallpox
Smallpox
Variola (Major & Minor)
• First virus to be
studied in detail
• Edward Jenner - 1798
• First vaccine - cowpox
virus (vaccinia virus)
Child with smallpox
Last case
of smallpox
(Ali Maow of
Merka, Somalia,
contracted
smallpox in
1977 at the age
of 23. His was
the last known
case of
smallpox in the
world.)
Icosahedral Virus
(many sides)
Polio - Naked, small, icosahedral virus
Wart virus
Enveloped Virus
INFLUENZA VIRUS
Children with measles
(uncommon today)
BACTERIOPHAGE
E-Coli Bacteria
Attachment of a phage to the cell
wall of E-Coli
Temperate vs. Virulent Viruses
HERPES ZOSTER (“Shingles”)
HERPES VIRUS
HERPES
Retroviruses
• RNA viruses
• Reverse transcriptase
- makes DNA from
its RNA
• Includes HIV, polio &
some cancers
HIV
Retrovirus Cycle
The Immune System
Bozeman Biology
http://www.youtube.com/watch?v=L
8oHs7G_syI
13:47 min.
HIV /
AIDS
When HIV Becomes AIDS (HIV
#2)
http://www.youtube.com/watch?v=6
8I7JlVhuhY
3:56 min
Louis Pasteur - discovered a
vaccine for rabies
Animal Rabies in U. S.
1999