Viruses
Viruses
What are they?
How do they work?
Where do they come from?
And… What good are they?
What is a virus?
An infectious agent made up of:
a core of nucleic acid – DNA or RNA and
(ONLY ABOUT 5 GENES)
a protein coat (capsid)
How Big are viruses?
Polio virus = 20 nanometers
20nm
1 nm – 0ne billionth of a meter!
3000 polio viruses fit across the diameter of a
period at the end of a sentence in your book.
They
havehave
no envelope
Some viruses
no envelope –
they’re naked!
Some viruses have an
envelope to cover them!
Envelope – came from host’s
cell membrane when virus
budded out of host
Viruses don’t reproduce…..
They Replicate.
Once inside a cell, the cell
does all the work and
produces new viruses using
the inserted DNA or RNA as a
guide.
1. Attachment
The lytic cycle
Lytic Cycle
a
2. injection
5. Lysis
3. replication
4. assembly
Are viruses living or nonliving?
What are some characteristics of life?
Do viruses exhibit these characteristics?
When were viruses discovered?
Viruses have apparently always been around.
However, it wasn’t until 1897 that tobacco
mosaic virus was discovered – it was causing
the tobacco plants to shrivel and be unusable.
Other plants can get TMV – tomatoes, for
example. Don’t smoke in a greenhouse.
Classification of Viruses
1. By Shape
2. Host type
3. function
Retroviruses
attack a certain
way.
Animal viruses
DNA viruses attack
another way.
Plant viruses
Bacteria viruses
Retroviruses
Contain RNA
When infecting a cell, these viruses
have to first change the RNA to DNA.
Once part of the cell’s Dna, the viral
code can cause the cell to make more
viruses.
HIV is one of these.
Nonviral infectious agents
• VIROIDS
– Single strand of
RNA
– Causes plant
diseases
How do Prions work?
•Prions
–PIECE OF PROTEIN
–CAUSE OF MAD-
COW DISEASE
–CAN INFECT
ANIMALS –
INCLUDING
HUMANS
Human diseases caused by
viruses
•
•
•
•
•
•
•
•
Common cold
Influenza (flu)
Chickenpox
Polio
HIV
Some pneumonia
Some meningitis
herpes
Viruses in the biosphere
• Animal diseases
– Distemper
– Rabies
– pneumonia
• Plant Diseases
– Discolor leaves
– Stunt growth
– Kill plants
Uses for viruses
• Vaccines – dead or weakened form that
stimulates the immune system to fight the
virus when exposed to it.
• Genetic engineering – use a virus carrier to
insert genes into diseased cells.
• Agriculture
– Pest control
– Colorful variations in some plants - flowers
Interesting Viruses
• Ebola virus – kills quickly; requires close
contact, such as when preparing a body for
burial or using dirty needles; since it kills so
fast, it generally dies out quickly.
• Human sarcoma virus –
causes tumors
• Adenovirus – causes
The Common cold – There
Are over 200 different
Cold viruses
Bacteriophages – infect bacteria; very
well studied.
Smallpox – once wiped out entire nations, now a
memory –
Most successful vaccination program in world.
Smallpox virus
Aren’t you glad
there’s no smallpox
anymore?
Vaccines – dead or
weakened form of virus
injected to provide
immunity.
First vaccine
• Chinese had been using
the idea for centuries,
but didn’t market it.
• Dr. Edward Jenner noticed that
milkmaids who had had cowpox
rarely got smallpox.
– Injected a boy with cowpox pus – he got
cowpox
– When injected with smallpox pus, he did
not get it!
The end