2. VIRUS “virus” is Latin for poison
An infectious agent made of nucleic acid and a protein covering.
A person who studies viruses is called a virologist.

3. Characteristics of Viruses
½ to 1/100 (100 times smaller) the size of a bacterium
Non living (not made of cells)
No respiration
No growth
No movement
Named for organism they infect or disease they cause
Only “alive” when inside a HOST cell
Do NOT grow-only reproduce inside a host

4. Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell
The size of a virus is very small in comparison to an animal cell or even a bacterium

5. Viral Structure
Viruses are made up of a nucleic acid (DNA or RNA…but NEVER both!)
The nucleic acid is enclosed in a protein coat called a CAPSID.
Some viruses are surrounded by an envelope or spiky outer covering used for extra protection.
Viruses have diverse sizes and shapes.

6. Figure 18.2 Viral structure
BINAL / COMPLEX
HELICAL
POLYHEDRAL
GLOBULAR

7. Parts of a Virus Capsid (protein coat) Nucleic Acid (DNA) Tail
Tail Fibers

8. Infection
Viruses cannot reproduce on their own—they REPLICATE by using a HOST cell
Infects a host cell
HOST: A living organism in which a virus is found
Has a matching surface receptor for host cell (fits like a puzzle)
3D shape determines which cells virus infects
If it can’t attach – it doesn’t infect

9. Viral Infection
Can not be “Killed” with the use of antibiotics because viruses do not have cell walls. (Antibiotics puncture cell walls)
Must be killed by the body’s own immune system (WBC and antibodies)
Once the virus is inside the host cell, two different processes may occur.

10. Viral Cycles Lytic Cycle:
Virus enters the cell, makes copies of itself and causes the cell to burstVirus lyses the host cell quickly and then releases hundreds of virus particles that infect other cells.
Lysogenic Cycle: Virus may “hide” in the host cell for a long period of time until causing symptoms of infection.
While hiding the virus

11. Figure 18.4 The lytic cycle of phage T4
Cell is lysed quickly

12. LYTIC CYCLE 2. Inject 1. Attach 3. Make parts 5. Release / lysis
4. Assemble

13. Bacteria cell being lysed

14. Figure 18.5 The lysogenic and lytic reproductive cycles of phage , a temperate phage
LYSOGENIC CYCLE

15. Figure 18.7x1 HIV infection
The HIV virus is an example of a lysogenic virus. Can be undetected for years because no symptoms are present. Can only be detected through blood testing.

16. Figure 18.7x2 Couple at AIDS quilt
The HIV epidemic is greatly affecting all nations, including US!
Africa is extremely affected.

17. Virus that Causes Smallpox is evident in this child.
Figure 18.x1 Smallpox
Virus that Causes Smallpox is evident in this child.

18. A virus causing measles can now be prevented with the use of vaccines.
Figure 18.x2 Measles
A virus causing measles can now be prevented with the use of vaccines.
Vaccines are a weakened/dead virus that allows the body to create a resistance (antibodies) against the harmful strain.

19. Figure 18.x3 Polio
Polio

20. Hepatitis strains vary and plague all nations.
Figure 18.x4 Hepatitis
Hepatitis strains vary and plague all nations.

21. Figure 18.8x Deer Mouse
The Haunta Virus plagued Southwestern region of the US in late 1990’s. Killing several people. It was transferred through rodents.

22. Figure 18.x5 Influenza epidemic

23. Figure 18.9 Viral infection of plants

24. Figure 18.9x Tobacco mosaic virus

25. Figure 18.x6 Herpes
A cold sore (herpes virus) is a lysogenic virus that integrates some of its nucleic acid into your DNA and reappears.

26. Figure 18.8 Emerging viruses
Although viruses are not a living organism they have the ability to MUTATE and do that rather well…Leading the the emergence of new virons.

27. Retrovirus
A certain type of virus that contains RNA instead of DNA. Once in the host, it transcribes its RNA into DNA using an enzyme called reverse transriptase. It then inserts the new DNA into the host’s DNA. Virus uses the cell to make itself.
Example: HIV: Human Immunodeficiency Virus (Causes AIDS)

28. Viroids & Prions
Viroids: similar to a virus. Infects only plants. Contains RNA and has no capsid.
Prion: similar to a virus. Infects only animals. Made of protein only. Does not have RNA or DNA.
Example…Mad Cow Disease