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CONTENTS
1. Introduction
4. Virology
2. Virus Structure
5. Virus and Medicine
3. Virus Replication
6. Review
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Introduction – Structure – Replication – Virology – Medicine - Review
We have all gotten viruses…
from bacteria, plants to animals.
Viruses cause colds, flu, warts and diseases
such as measles, AIDS and cancer.
BUT not all viruses cause diseases,
AND not all viruses are harmful to humans.
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Introduction – Structure – Replication – Virology – Medicine - Review
WHAT IS A VIRUS?
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Introduction – Structure – Replication – Virology – Medicine – Review
A VIRUS is either DNA or RNA, that is protected by a protein
coat called a CAPSID.
DNA
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CAPSID
VIRUS
Introduction – Structure – Replication – Virology – Medicine - Review
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Why are some viruses harmful?
Virus invades cell
Virus forces cell to make copies of virus
When your cells
make viruses
instead of
operating normally,
YOU get sick
Eventually so many copies are
made, the cell explodes,
releasing all of the new viruses
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Introduction – Structure – Replication – Virology – Medicine - Review
Examples of some viral diseases:
DISEASE
VIRUSES
AIDS
HIV
Wart
Flu
Measles
Cancer
Herpes Simplex
Virus
Influenza
Morbillivirus
.
Hepatitis B
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Introduction – Structure – Replication – Virology – Medicine - Review
Who do viruses infect?
Viruses usually infect a specific host including:
• 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
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Introduction – Structure – Replication – Virology – Medicine - Review
Let’s look at the Defining
Properties of Viruses
• Viruses are parasites that invade cells
• Viruses have either DNA (Deoxyribose Nucleic
Acid) or RNA (Ribonucleic Acid)
• Viruses direct the synthesis of new virus within
a host cell.
• Newly made viruses infect other cells.
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Introduction – Structure – Replication – Virology – Medicine - Review
Cell Biology
Let's review a little cell biology since viruses cannot multiply without the
help of cells. The viruses enter the cell and forces the cell to make more
viruses.
nucleus
The cell has three main zones:
Nucleus – this holds the
DNA or genetic
information about the
cell.
Cytoplasm – this is the
“factory” where biochemical
reactions occur.
Membrane – this double layer
protects the cell and allows the
cell to communicate with the
outside environment.
cytoplasm
membrane
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Introduction – Structure – Replication – Virology – Medicine - Review
DNA/RNA
DNA or RNA code for genes that defines who we are.
DNA, deoxyribonucleic acid, is
the double-stranded molecule
that encodes genetic
information (e.g. your hair color,
height, etc.) in the nucleus of
cells. The complete set of DNA
in a cell is called the genome.
RNA, ribonucleic acid, is
typically single stranded so that
it can be read to make proteins.
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Introduction – Structure – Replication – Virology – Medicine - Review
How small is a virus?
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Introduction – Structure – Replication – Virology – Medicine - Review
Viruses range in size from 20 nanometers (nm) – 250 nanometers (nm)
1 nm = 0.00000004 inches
atom
proteins
If a cell was the size of your classroom, then an average virus would be
the size of a softball.
viruses
0m
animal
cells
bacteria
10-6 m
10-5 m
10-7 m
10-8 m
10-9 m
Go five more feet!
10-10 m
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Helical Capsids
RNA
Helical capsids are rodlike structures with the
RNA in the center of the
helix. A helix is made by
stacking repeating units in
a spiral.
protein coat
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Introduction – Structure – Replication – Virology – Medicine - Review
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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Introduction – Structure – Replication – Virology – Medicine - Review
Adenovirus
Adenoviruses cause diseases like pink-eye or the common cold
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Introduction – Structure – Replication – Virology – Medicine - Review
Bacteriophage
Bacteriophage is a virus that infects bacteria.
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Introduction – Structure – Replication – Virology – Medicine - Review
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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Introduction – Structure – Replication – Virology – Medicine - Review
How do viruses replicate?
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Introduction – Structure – Replication – Virology – Medicine - Review
Replication Phases
I, II, III - Viruses enter cell
-
Attachment to cell membrane
Penetration inside cell
Losing virus protein coat
Phase I
IV - Replication
-
Tricks cell into making
more viral DNA
Tricks cell into
making viral protein
coat
V - Release
-
-
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Assembly of virus
DNA and protein
coat into whole
new viruses
Leaving the cell
Phase II
Phase III
Phase IV
Phase V
http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/adlyt.html
Introduction – Structure – Replication – Virology – Medicine - Review
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The concept of a virus as an organism
challenges the way we define life:
*
*
*
*
Viruses do not breathe.
Viruses do not metabolize.
Viruses do not grow.
However, they do reproduce.
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Introduction – Structure – Replication – Virology – Medicine - Review
Are Viruses Living?
Create 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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Introduction – Structure – Replication – Virology – Medicine - Review
A Brief History of Virology
1898
1880 – Germ Theory
100BC – China
Protection from smallpox
using variolation practice
~1400BC
First written record of
virus infections in
heiroglyphics found in
Memphis, Eygpt
Robert Koch & Louis Pasteur
Pasteur identified rabies to be
cause by an agent he termed
“virus” from the Latin for ‘poison’.
1796 Vaccination
Edward Jenner
vaccinated a boy with
cowpox-infected
material
Martinus Beijerinick
work on TMV
Freidrich Loeffler &
Paul Frosch work on
foot-and-mouth
disease in cattle
1892 beginning
of virology
Dmitri Iwanowski showed
that ceramic filtered
extracts from diseased
plants could transmit
disease to other plants.
1915-1917
Bacteriophages
(eaters of
bacteria)Frederick
Twort & Felix
d’Herelle discovered
viruses which infect
bacteria.
1909
Landsteiner &
Popper
Poliomyelitis (Yellow
Fever) was the first
human disease to be
recognized as a viral
disease
19502003
Discoveries of
Ebola, West
Nile, HIV, SARS
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Introduction – Structure – Replication – Virology – Medicine - Review
Techniques to Study Viruses
X-ray Crytallography – X-rays are
directed at a sample. How those rays
scatter can be used to determine the
structure of that sample
Atomic Force Microscope – A tiny tip
probes a surface, from which the shape
of the surface can be determined
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Sedimentary
Centrifugation – A
sample is spun so fast,
different elements in
it are separated by
density
Filters – Very
small holes in
material filter only
viruses through
Electron Microscope –
Electrons are smaller
than light wavelengths,
so viruses can be
“seen” by reflecting
electrons off of them
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Viruses Can Help Cells, Too
- Since viruses can transport DNA and RNA
into cells, scientists are exploring Gene
Therapy
- In Gene Therapy, viral genetic material is
replaced with new DNA
- In time, this could be used to cure genetic
diseases. Currently we have no cure for
these types of illnesses
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Introduction – Structure – Replication – Virology – Medicine - Review
The End! And Review
• Viruses are very simple: a shell containing
either DNA or RNA.
They infect by hijacking cells’ machinery to
force them to make more viruses.
• Viruses are tiny, even compared to a cell.
• Some viruses may prove useful in gene
therapy as natural carriers of DNA that was
specially designed to be good for a particular
reason.
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Introduction – Structure – Replication – Virology – Medicine - Review
The End
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Introduction – Structure – Replication – Virology – Medicine - Review
VIRUS
A living thing that
provides a source of
energy for a virus or
A tiny, nonliving that invades and
an organism
Organisms that
live on or near
a host and
cause it harm.
then multiplies inside of a cell.
A virus that immediately goes into
action. It begins to take over cell
functions and produce the virus’s
proteins and genetic material.These
parts then assemble into new viruses.
The viruses multiply like a copy machine
left on. When it is full it bursts open –
releases the new viruses and dies.
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Some viruses hide for a while and become part of the cell’s
genetic material. It may stay inactive and “hidden” for years.
Then under certain conditions it becomes active and acts like
an active virus. Ex – cold sores
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- Viruses
How Viruses Multiply
•Active viruses enter cells and
immediately begin to multiply, leading to
the quick death of the invaded cells.
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- Viruses
How Viruses Multiply
•Hidden viruses “hide” for a while inside host
cells before becoming active.
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- Viruses
Active and Hidden Viruses
Activity
•Click the Active Art button to open a
browser window and access Active Art
about active and hidden viruses.
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- Viruses
Deadly Virus
•Click the Video button to watch a movie
about deadly viruses.
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- Viruses, Bacteria, and Your Health
Common Viral Diseases
•Unlike with bacterial diseases, there are
currently no medications that can cure viral
infections.
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