3. 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.
BACK NEXT
5. A VIRUS is either DNA or RNA, that is protected by a protein
coat called a CAPSID.
DNA CAPSID
VIRUS
BACK NEXT
6. 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
BACK NEXT
7. Examples of some viral diseases:
DISEASE VIRUSES
AIDS HIV
Wart
Herpes Simplex
Virus
Flu Influenza
Measles Morbillivirus .
Cancer Hepatitis B
BACK NEXT
8. 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
BACK NEXT
9. 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.
BACK NEXT
11. Viruses range in size from 20 nanometers (nm) – 250 nanometers (nm)
1 nm = 0.00000004 inches
If a cell was the size of your classroom, then an average virus would
be the size of a softball.
animal
bacteria cells
10-6 m 10-5 m
viruses
10-7 m
10-8 m
atom
0 m
proteins
10-9 m
10-10 m
Go five more feet!
BACK NEXT
13. Replication Phases
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
V - Release
- Assembly of virus
DNA and protein
coat into whole
new viruses
- Leaving the cell
Phase I
Phase II
Phase III Phase IV Phase V
BACK NEXT
14. 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.
BACK NEXT
15. 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
BACK NEXT
16. 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.
BACK NEXT
