VIRUSES
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BIOLOGICAL WARFARE
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STILL NOT FEELING WELL
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Flu
Rabies
Chicken pox
Mumps
Common Cold
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STILL NOT FEELING WELL
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SEXUALLY TRANSMITTED
DISEASES
AIDS
 Hepatitis
 Herpes
 HPV
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SEXUALLY TRANSMITTED
DISEASES
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STRUCTURE
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VIRUS
A
typical virus is
composed of a
core of DNA or
RNA surrounded
by a protein coat.
 The protein coat
is called a capsid.
 Viruses are NOT
alive. They are
not living things!
Receptor Site
The receptor site is the location on the cell where the
virus locks in.
 It is specific – a virus can only enter a cell if it matches
exactly!


Like pieces of a puzzle
Viruses have two life cycles
1. Lytic Cycle: Viruses-immediately infect
the host cell (FAST)
Small Pox- Lytic
Jenner developed first vaccine 1798
2. Lysogenic Cycle - lay dormant in the
cell, viral DNA incorporated into host
DNA, (SLOW)
Herpes Simplex 1/Lysogenic
Shingles-Lysogenic/ Chicken pox virus (herpes varicella-zoster)
Viral Infections
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Lytic infection –
a virus enters a cell,
makes copies of itself
and causes the cell to
burst.
 -Cold, Flu
Lysogenic
infection – virus mixes
its DNA with the DNA
of the host cell and the
virus replicates as long
as the body keeps
making new cells.
 -Herpes
Retroviruses

Contain RNA and not DNA
- to be able to take over a host cell, the retrovirus must be able
to convert the RNA into DNA
- to accomplish the conversion, retroviruses insert an enzyme
called Reverse Transcriptase into the host cell
Treatment
Vaccines are taken BEFORE a viral infection
occurs.
 Your immune system:
 Recognizes the weakened virus (vaccine)
 Targets them for destruction
 Remembers the virus so that the next time it
enters your cells it is automatically killed
 You never get sick!!!
 Unlike bacterial infections, viral infections
cannot be treated once you are infected.

Bacteriophage

Bacteriophages are viruses that infect bacteria
Characteristics of Viruses
 Not
Alive
- Must reproduce(replicate) inside a host
 Structure
- Nucleic Acid – DNA or RNA
- Protein coat – called a capsid
- Envelope – some contain a layer of membrane taken
from a host cell
 Mutate
Rapidly
 Host Specific
- can only infect one type of cell
 Small – from 20nm to 250nm
- most are too small to be seen with a light microscope
 Vaccines
used to prevent catching a virus