1. Viruses

2. What is a virus? Tiny, nonliving particles that can cause disease.
Remember the 4 characteristics of life?
Grow & Respond to Environment, Made of Cells, Reproduce, Obtain & Use Energy
Viruses are NOT considered to be a living organism because:
They DO NOT reproduce on their own. They must be inside a living cell
called the host cell.

4. Viral Structure Basic structure includes: Nucleic Acid Core
Capsid (Protein Coat)
Viral Envelope (found in some viruses)

5. Nucleic Acid Core Contains genetic material which is either DNA or RNA
The DNA or RNA is only instructions for making copies of the virus—nothing else.

6. Viral Shapes are determined by the capsid.
Polyhedral
Cylindrical
Spherical
Polyhedral Head w/Tail
Ex) Polio Virus
Ex) Tobacco Mosaic Virus
Ex) Influenza Virus (Flu)
Ex) Bacteriophage

7. Bacteriophage Virus that infects bacteria.
Bacteriophages can infect E. coli bacteria making it harmful to humans.

8. Importance of Shape
Allows virus to recognize and attach to specific host cell.
The shape is important in viral reproduction because it allows them to invade a host cell.
Some are species specific.
Can only infect certain species like a bacteriophage only infects bacteria.
Some are also cell-type specific.
Polio virus infects only human nerve cells.

9. Attachment and Entry

10. Viral Infection
Once inside the host cell, 2 different processes may occur.
Some replicate immediately, killing the host cell. (Lytic Cycle)
Others replicate in a way that does not kill the host cell immediately. (Lysogenic Cycle)
Let’s take a closer look…

11. Lytic Cycle
In a lytic infection , a virus enters a cell, makes copies of itself, and causes the cell to burst.

12. Lytic Cycle Animation

13. Lytic Cycle
Attachment
Entry
Replication
Assembly
Lysis and Release

14. Lytic Cycle Attachment- virus recognizes & attaches to host cell
Entry- viral DNA injected into cell
Replication- viral genes & capsids copied
Assembly- viral genes put together into protein coats
Lysis and Release- cell bursts & releases viral particles

15. Lysogenic Cycle Animation

16. Lysogenic Infection
Unlike lytic viruses, lysogenic viruses do not lyse the host cell right away. Instead a lysogenic virus remains inactive for a period of time.

17. Lysogenic Cycle Attachment & Entry Provirus formation DNA Replication
Cell Division
Lytic Cycle

18. Lysogenic Cycle Attachment & Entry
Provirus formation: Viral DNA embedded into host cell’s DNA
DNA Replication: viral DNA copied along with host DNA
Cell Division: Cell divides with viral DNA
Lytic Cycle: at any time the viral DNA leaves the host DNA and enters the lytic cycle

19. Lytic and Lysogenic cycles

20. Viral Diseases

21. HIV/AIDS
Retrovirus (Viruses that contain RNA as their genetic material) that is lysogenic.
Small numbers of HIV viruses bud off from infected white blood cells. They then infect other WBC. But the viruses are not killing the host at this time.
HIV turns into AIDs when the virus goes into the Lytic Cycle

22. Polio virus infects and kills cells of the nervous system, producing paralysis.
Human papillomavirus infects cells in the outermost layer of the skin, producing an abnormal growth known as a wart.

23. Treatment/Prevention
Unlike bacterial diseases, viral diseases cannot be treated with antibiotics. WHY??
The best way to protect against most viral diseases is to prevent them with vaccines.
Once the viral disease has been contracted, only symptoms of the infection can be treated.

24. Comparison Living, Prokaryotic Cells Reproduction: Treatments: Causes:
BacteriA
VIRUS
Living, Prokaryotic Cells
Reproduction:
Binary Fission (asexual)
Conjugation (sexual)
Treatments:
Anitbiotics
Vaccines
Causes:
Strep Throat
Tuberculosis
Lyme Disease
Bacterial meningitis
Tetanus
Non-living
Reproduction: MUST infect Host Cell
Lytic Cycle
Lysogenic Cycle
Treatments:
Symptoms ONLY!
Vaccines
Causes:
Common cold
Influenza (Flu)
AIDS
Warts
Hepatitis A, B, C
Polio
Chicken pox