Viruses
Have you heard of…?
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Avian Flu
West Nile
HIV
SARS (severe acute respiratory syndrome)
Chicken pox, measles, rabies, or polio
common cold
All caused by viruses.
Discussion: Is a virus a living thing?
Evidence for living:
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carry __________________
_________________________
_________________________
Characteristics of living things:
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Made up of ___________
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________________
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________________________
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________________________ (metabolism)
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________________________
Viruses are not considered living:
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not ______________- only made up of genetic material and
protein coat
do not ___________________________
o if undisturbed, ________________________
do not do anything in nutrient agar (grow nor die)
if undisturbed, __________________________
cannot _________________________ without a host cell
Do not ________________________________
Cannot _____________________________
Tobacco Mosaic Virus
History
In the late 1800’s something was infecting tobacco plantations,
causing bleached spots on the leaves forming a pattern the farmers
called a mosaic.
In 1892, Dmitri Ivanovsky investigated.
He looked for infectious agents by crushing leaves of infected
plants and passing juice of
crushed plants through a filter small enough to ______
________________________.
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He found the filtered juice from infected plants could still
cause disease to another plant. Ivanovsky declared the disease
was caused by a ______________________ too small to be seen
with the light microscope.
Martinus Beijerinck called the filtered, infectious substance a
"_______________" and this discovery is considered to be the beginning
of ___________________-.
The name “virus” means __________________________- in Latin.
1931: Electron microscope allows for first imaging of viruses.
Transmission Electron Microscopy (TEM) is a technique in which a
beam of electrons is transmitted through an ultra-thin specimen.
Although Louis Pasteur and Edward Jenner were the first to develop ____________________to protect against viral
infections, they did not know that viruses existed.
Smallpox virus was a major cause of death in the 20th century, killing about 300 million people.
Smallpox virus was a major cause of death in the 20th century, killing about 300 million people.
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Smallpox virus was a major cause of death in the 20th century, killing about _______________________.
Symptoms:
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high fever.
chills.
malaise.
headache.
severe back pain.
abdominal pain.
vomiting.
Edward Jenner developed __________________:
Edward Jenner (1749–1823), a rural physician, contracted small pox as a boy. Jenner knew of a local belief that dairy
workers who had contracted a relatively mild infection called cowpox were immune to smallpox. In 1796 he
inoculated an 8 year old boy with Cow Pox.
Jenner then took some "_____________________" and repeatedly inoculated the boy who survived and was
subsequently immune to smallpox.
The word ___________________is derived from the Latin _______________meaning "cow".
Louis Pasteur developed Rabies Vaccination:
 In France cures were desperately sought for rabies.
Rabies is a viral disease that causes acute inflammation of the brain in warm-blooded animals.
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Pasteur (1822–1895) looked for the "_______________________" in mad dogs.
 Pasteur showed that when the dried ________________________ from
dogs that had died from rabies were crushed and injected into healthy dogs they did not become
infected. He repeated the experiment several times on the same dog with tissue that had been dried for
_______________________, until the dog survived even after injections of
________________________________.
 Pasteur had immunised the dog against rabies.
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Definitions
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A virus is a _______________________________________________________________
___________________________________.
Acts _______________ by entering a host cell and using the material in the host cell to
reproduce.
_______________ is the study of viruses and the diseases they cause.
 Bacteriophage is a virus that infects bacteria.
 Viron is the ____________________________________________________________
 A ___________________is a bacteriophage (often shortened to "phage")
___________________inserted and integrated into the host bacterial DNA.
 ____________________ means that a virus can only attack particular cells
of a particular organism.
Eg. Polio virus attacks nerve cells
Mumps virus attacks salivary glands
 ____________________ is an RNA viruses that inserts a DNA copy of their
genome into the host cell in order to replicate (e.g. HIV).
Structure
Viruses are ___________________-they lack most of the components
of cells, such as organelles, ribosomes, and a plasma membrane.
All viruses consist of:
 a nucleic acid core (consisting of either RNA or
DNA),
 an _____________________ or
____________________ that encases the nucleic
acid,
 sometimes an ____________________ of lipid
(fat) and protein molecules that is used to enter
host cell (host lipid membrane cannot detect viral
lipid membrane)
TEM image of a group of typical head and tail bacteriophage.
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Shape
Viruses come in many shapes and sizes, but these are __________________ and
____________________ for ______________________. In general, the shapes of viruses are
classified into four groups:
Filamentous
Isometrical
Enveloped
(Helical)
(Polyhedral)
(Spherical)
Complex
(Head and Tail)
Filamentous viruses
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are long and ______________________.
Many plant viruses are filamentous, including TMV (tobacco mosaic virus).
Isometric viruses
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have shapes that are roughly ___________________,
poliovirus or herpesviruses.
Enveloped viruses
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____________________________________________________________.
Animal viruses, such as HIV, are frequently enveloped.
Complex Head and tail viruses
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Size
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infect _________________________.
They have a head that is similar to icosahedral viruses and a tail shape like filamentous
viruses.
viruses can be up to ______________ than bacteria.
17-1000 nanometers
(1000nm = 1 micrometer)
http://www.cellsalive.com/howbig_js.htm
Replication
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Viruses exist in ______________________
When not in contact with a host cell, the virus remains
_______________________.
o During this time the virus is static - no internal
biological activities occurring within the virus,
o _____________ can remain in this dormant
state for extended periods of time, until they come into contact with the
appropriate host, at which time it becomes ____________________ and is then
referred to as a _________________. It now displays properties typified by living
organisms, such as ________________ _________________ and directing its
efforts toward _____________________.
http://highered.mheducation.com/sites/0072995246/student_view0/chapter8/lambda_phage_
replication_cycle.html
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LYTIC CYCLE
 Used by most viruses
 Produces symptoms immediately
1. Attachment:
- to host cell (All viruses have some type of protein on the outside coat that "recognizes"
the proper host cell.)
2. Penetration:
- genetic material _______________________________
- or host cell engulfs virus by process called __________________________
- genetic instructions released into the host cell,
- the injected genetic material ____________________ to the host cell's enzymes
3. Replication and protein synthesis:
- host is directed to make __________________________ and protein
-host cellular ____________________ make parts for more new virus particles
4. Assembly:
- of _________________________________
- the new particles assemble into ______________________.
5. Release:
- the new viral particles (virions) rupture the cell
- process called ____________________________.
- The new virus particles leave the host cell, ready to infect other cells
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LYSOGENIC CYCLE
 Produces symptoms some time after
 Host cell not lysed right away
 Steps 1 & 2
3b. Viral genetic material inserts into DNA of host cell
- call a ______________________
- host DNA continues to function
- may remain in host DNA for ________________________
4b. as host cell replicates, viral genetic material is also copied to the new cells of the host
- viral genetic material remains ________________________________
- ___________________________________
- ___________________________________
- activates to direct synthesis of new virions via the Lytic Cycle steps 3-5
Classification
Viruses are generally classified according to their:
 ________________________
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________________________
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________________________
________________________
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1962: Linnaean hierarchical system
Order (-virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species (-virus)
Species names generally take the form of [Disease] virus.
Eg Small pox Variola major and Variola minor
2013: Baltimore Classification system: seven groups depending their nucleic acid
No viral genome encodes a complete system for
translating proteins; therefore all viral protein
synthesis is completely dependent upon the
translational machinery of the cell. David Baltimore
created his virus classification scheme based on the
the importance of viral genome in programming
viral protein synthesis.
Role of Viruses in Ecosystem
Viruses are immensely important to the
turnover of biomass in many
ecosystems.
A teaspoon of seawater contains about
one million viruses.
Microorganisms constitute more than
90% of the biomass in the sea. It is
estimated that viruses kill approximately
20% of this biomass each day, and that
there are 15 times as many viruses in the
oceans as there are bacteria. Viruses are the main agents responsible for the rapid destruction
of harmful algal blooms, which often kill other marine life.
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https://youtu.be/1PLBmUVYYeg
http://sploid.gizmodo.com/clever-animation-explains-how-viruses-attack-our-cells1564551563?utm_campaign=socialflow_gizmodo_facebook&utm_source=gizmodo_facebook&
utm_medium=socialflow
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