1. Viruses
Alive or not?

2. There are many viruses that affect humans. Here are a few of them.
The AIDS Virus

3. Herpes simplex
virus

4. Smallpox virus

5. Different types of Influenza viruses

6. Measles virus

7. Ebola Virus

8. Viruses attack specific species and often specific cells
Viruses attack specific species and often specific cells. A virus that would affect a human would not affect different organism.
Bacteriaphage viruses attack
only bacteria
Tobacco Mosiac virus
Attacks tobacco plants

9. Viruses remained undiscovered for so long because they are very small.
Human Skin Cell
Bacteria
Viruses

10. The very first virus discovered on the 12th February 1892 by Dmitri Iwanowsk ( ), a Russian botanist. While studying mosiac tobacco disease, he found that the agent causing the disease
was small enough for pass
though ceramic filter that are
small enough to trap all bacteria.
This is generally accepted as
the beginning of Virology.

11. So what is a virus? The virus is made up of 2 basic structures:
1. A core of DNA or
RNA
2. A protein coat
surrounding the
DNA or RNA called
a capsid
Sometimes they have
tail fibers that help them
attach to a host cell.

12. Viral reproduction is quite fascinating!
1. The virus
attaches to the
membrane of a
host cell.

13. 2. The virus injects its genetic material
into the host cell.

14. The viral DNA is replicated by the host
cell.

15. 4. The viral DNA and protein coats
are produced by the host cell.

16. 5. The parts of the virus assemble

17. 6. Viral enzymes break down the membrane
causing the host cell to split open.
Now the new viruses infect neighboring cells.

18. So how can you fight a viral infection?
There are no medications or drugs that can help you get rid of a virus.
Antibodies are produced in the blood (yellow) which are specific to the attacking virus (green)
The antibodies disable
the virus but only after
you have felt the
affects of the
illness

19. Prevention of Viruses
Viral infections can be prevented with a vaccine.
A vaccine is a liquid that contains a weakened form of the virus (usually the protein coat)
This fools the body into producing antibodies so that when the real virus attacks, the body is ready to disable it.

20. Types of Vaccinations you have received.
Tetanus
Influenza
Polio
Mumps
Measles
Rubella
Chicken pox
Hepatitis

21. How to avoid getting and spreading the flu virus
Wash your hands often
Get plenty
Of rest
Drink lots of water
Get a flu shot
Avoid sick people
Don’t eat at
buffets 
Eat healthy foods
Like fruits and
vegetables

22. How do viruses and cells compare?
Reproduction:
Viruses- only reproduce with a host cell
Cell- independent cell division
Genetic Code:
Virus- DNA or RNA
Cell- DNA
Growth and Development:
Virus- no
Cell- yes, cells increase in
size and number

23. Obtain and Use Energy:
Virus- no
Cell- yes
Respond to the environment: Virus- no
Cell- yes
Change over time:
Virus- yes
Cell- yes

24. What do you think? Are viruses alive?
Give evidence to support this opinion:
YES NO