1. Viruses – Cellular Pirates
Enteric Adenovirus is an Icosahedral virus - common shape
Chicken Pox – contains an envelope – membrane taken from the host – contains host glycoprotein trick the host cell into taking in the virus 1

2. Characteristics of Viruses
Obligate Intercellular Parasite
- Must reproduce (replicate) inside a host
Structure
- Nucleic Acid – DNA or RNA
- Protein coat called a capsid
Mutate Rapidly
Host Specific can only infect one type of cell
Small – from 20nm to 250nm most are too small to be seen with a light microscope 2

3. Anatomy of a Virus

4. Virus Structure
Helical virus – hollow tube of protein, icosahedron, phage 4

6. Bacteriophage Bacteriophages are viruses that infect bacteria
- they are responsible for transduction in bacteria 6

7. Viruses have two life cycles
Lytic Cycle-Viruses immediately infect the host cell
Lysogenic Cycle – Viruses lay dormant in the cell before infecting the host cell. 7

8. Lytic Cycle 8

9. The Lytic Cycle

10. Small Pox- Lytic Jenner developed first vaccine 1798
Small pox virus can only live in humans. Spread person to person generally through close contact with infected person. Symptoms appear 12 –14 days after exposure. 1st symptoms are fever, tiredness, severe back pain, stomach pain and vomiting. This last 2-3 days and at this time the person is highly contagious to others.Then over the next 5 days the bumps appear. Today we have a vaccine for small pox. We have 15.5 million doses available now. A contract has been made to produce 210 million does this year!! Today the risk of the disease is less than the risk from the vaccine so people do not get vaccinated. Vaccine can be helpful if you are exposed up to 4 days after exposure. 10

11. Lysogenic Cycle 11

12. The Lysogenic Cycle

13. Herpes Simplex 1/Lysogenic13

14. Shingles-Lysogenic/ Chicken pox virus (herpes varicella-zoster)
Shingles is caused by the chicken pox virus. It can develop in anyone who has had chicken pox. The chicken pox virus remains dormant or inactive (lysogenic cycle) in nerve root cells of the body. Shingles is the second outbreak of the chicken pox virus. Usually happens in older people (65) because of weakened immune system.Typical case of shingles lasts about a month. If you get it on your face you should see a physician because it can led to blindness. 14

15. Lytic and Lysogenic Cycles15

17. Retroviruses Contain RNA and not DNA
- To be able to take over a host cell, the retrovirus must be able to convert the RNA into DNA.
-To accomplish the conversion, retroviruses insert an enzyme called Reverse Transcriptase into the host cell

18. RETROVIRUSES Most complicated
Genetic information flows in the reverse direction
Have the enzyme reverse transcriptase
Transcribes DNA from an RNA template
The host’s RNA polymerase transcribes the viral DNA into RNA molecules.

19. HIV is a retrovirus injecting the enzyme, reverse transcriptase into the cell to copy viral RNA into DNA.

20. Viruses are host specific – a protein on the surface of the virus
has a shape that matches a molecule in the plasma membrane
of its host, allowing the virus to lock onto the host cell.

21. HIV doesn’t target just any cell, it goes right for the cells that want to kill it. “Helper" T cells are HIV's primary target. These cells help direct the immune system's response to various pathogens.