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Discovery of VirusesDiscovery 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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We have all gotten viruses…
from bacteria, plants to animals.
Viruses cause colds, flu, warts and diseases
such as measles, AIDS and cancer.
AND not all viruses are harmful to humans.
BUT not all viruses cause diseases,
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• Non living structures
• No cellular
• Contain a protein coat called the
capsid
• Have a nucleic acid core containing
DNA or RNA
• Capable of reproducing only when
inside a HOST cell
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• 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
DNA
SPIKES
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•Outside of host cells,
viruses are inactive
•Lack ribosomes and
enzymes needed for
metabolism
•Use the raw materials
and enzymes of the host
cell to be able to
reproduce
EBOLA VIRUS
HIV VIRUS
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Why are some viruses harmful?
Virus invades cell
Virus forces cell to make copies of virus
Eventually so many copies are
made, the cell explodes,
releasing all of the new viruses
When your cells
make viruses
instead of
operating normally,
YOU get sick
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DISEASE VIRUSES
AIDS HIV
Wart
Herpes Simplex
Virus
Flu Influenza
Measles Morbillivirus .
Cancer Hepatitis B
Examples of some viral diseases:
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How the viruses infect ?
• Viruses infect Bacteria
– These viruses are called Bacteriophages
• Viruses infect Plants
– One example is the Tobacco Mosaic Virus
• Viruses infect Animals
– One example is the common cold
Viruses usually infect a specific host including:
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•Viruses areViruses are smaller than thesmaller than the
smallest cell.smallest cell.
•Measured inMeasured in nanometers.nanometers.
•Viruses couldn’t be seen untilViruses couldn’t be seen until
thethe electron microscopeelectron microscope waswas
invented in theinvented in the 2020thth
century.century.
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Viruses range in size from 20 nanometers (nm) –
250 nanometers (nm)
10-5
m10-6
m
10-7
m
10-8
m
10-9
m
10-10
m
0 m
viruses
animal
cellsbacteria
proteins
atom
Go five more feet!
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Viral ShapesViral Shapes
•Viruses come in a variety of shapes
•Some may be helical shape like the
Ebola virus
•Some may be polyhedral shapes like
the influenza virus
•Others have more complex shapes
like bacteriophages
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Helical Capsids
Helical capsids are rod-
like structures with the
RNA in the center of the
helix. A Helix is made by
stacking repeating units in
a spiral.
RNA
protein coat
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Tobacco Mosaic Virus
Tobacco Mosaic Virus (TMV) is an example of a virus with a helical
structure. Protein subunits wrap around the spiraling RNA strand.
This image taken using an Electron Microscope
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Enveloped Viruses
Enveloped viruses are viruses which have a membrane coat
surrounding the protein coat or capsid. These viruses are common
in animal viruses, but are uncommon in plant viruses.
Herpes Simplex Virus.
A membrane (made of proteins)
surrounds the capsid (also made of
proteins) which surrounds the viral
DNA.
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Replication Phases
V - Release
- Assembly of virus
DNA and protein
coat into whole
new viruses
- Leaving the cell
Phase I
Phase II
Phase IV Phase VPhase III
I, II, III - Viruses enter cell
- Attachment to cell membrane
- Penetration inside cell
- Losing virus protein coat
IV - Replication
- Tricks cell into making
more viral DNA
- Tricks cell into
making viral protein
coat
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Are Viruses Living?
A table where one column represent properties of living
organisms and the second column represent properties of a virus.
Properties of Living
Organisms
Properties of Viruses
Breathes (respires) Doesn’t breathe
Metabolizes Doesn’t metabolize
Grows Doesn’t grow
Reproduces Reproduces
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Atomic Force Microscope – A tiny
tip probes a surface, from which the
shape of the surface can be
determined
X-ray Crystallography – X-rays
are directed at a sample.
Techniques to Study Viruses
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Filters – Very
small holes in
material filter only
viruses through
Sedimentary
Centrifugation – A
sample is spun so fast,
different elements in
it are separated by
density
Electron Microscope
– Electrons are smaller
than light wavelengths,
so viruses can be
“seen” by reflecting
electrons off of them
