Beijerinck (1897) coined the Latin name “virus” meaning poison He studied filtered plant juices & found they caused healthy plants to become sick

1. VIRUS

2. 2
Viral History
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3. 3
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
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4. 4
Tobacco Mosaic Virus
Wendell Stanley
(1935) crystallized
sap from sick tobacco
plants
He discovered
viruses were made of
nucleic acid and
protein
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5. 5
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
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6. 6
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
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7. CHARACTERISTICS OF VIRUS
is non-cellular particles.
reproduces through infect living cells.
it is made up of nucleic acids (DNA or
RNA)
It has variety of shapes

8. 8
Characteristics
Some viruses are
enclosed in an protective
envelope
Some viruses may have
spikes to help attach to
the host cell
Most viruses infect only
SPECIFIC host cells
CAPSID
ENVELOPE
DNA
SPIKES
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9. 9
Size of Viruses
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10. 10
Characteristics
Viral capsids
(coats) are made
of individual
protein subunits
Individual
subunits are called
capsomeres
CAPSOMERES
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11. Virus Morphology
Helical
Icosahedral

12. 12
Helical Viruses
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13. 13
Polyhedral Viruses
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14. 14
Complex Viruses
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15. 15
5 Steps of Lytic Cycle
1. Attachment to the cell
2. Penetration (injection) of viral DNA
or RNA
3. Replication (Biosynthesis) of new viral
proteins and nucleic acids
4. Assembly (Maturation) of the new
viruses
5. Release of the new viruses into the
environment (cell lyses)
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16. 16
Attachment Phage attaches by tail fibers to
host cell
Penetration Phage lysozyme opens cell wall,
tail sheath contracts to
force tail core and DNA into cell
Biosynthesis Production of phage DNA
and proteins
Maturation Assembly of phage particles
Release Phage lysozyme breaks cell wall
Lytic Cycle Review
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17. 17
Attachment:
Phage
attaches to
host cell.
Penetration:
Phage pnetrates
host cell and
injects its DNA.
Merozoites
released into
bloodsteam from
liver may infect
new red blood cells
1
2
3
Bacterial
cell wall
Bacterial
chromosome
Capsid DNA
Capsid
Sheath
Tail fiber
Base plate
Pin
Cell wall
Tail
Plasma membrane
Sheath contracted
Tail core
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18. 18
4 Maturation:
Viral components
are assembled into
virions.
Tail
5 Release:
Host cell lyses
and new virions
are released.
DNA
Capsid
Tail fibers
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19. Transmission of Viruses
1. Respiratory transmission
Influenza A virus
2. Faecal-oral transmission
Enterovirus
3. Blood-borne transmission
Hepatitis B virus
4. Sexual Transmission
HIV
5. Animal or insect vectors
Rabies virus

20. 20
Treatment for Viral
Disease
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1. A vaccine against a viral disease can be made from an
attenuated, less virulent strain of the virus.
2. Interferons are naturally occurring proteins made by cells
to fight viruses
3. Genetic altering of viruses (attenuated viruses)
4. Antiviral drugs (AZT)
Protease inhibitors – prevent capsid formation