1. Wednesday/Thursday 4/13-4/14/2016
Virus & Bacteria
Wednesday/Thursday 4/13-4/14/2016
Agenda:
Activity: Brain Pop
Notes: Discovery of Viruses
Activity: Lytic vs. Lysogenic Video
Homework:
No Homework Today!!
STAMP SHEETS DUE TODAY!!

2. Discovery of Viruses
At the end of the 19th century, scientists began researching the cause of Tobacco Mosaic Disease: stunts the growth of tobacco plants.
Scientists filtered bacteria from the sap of infected tobacco plants.
FINDING: Filtered sap could still cause uninfected plants to become infected.
CONCLUSION: The pathogen is smaller than a bacterium; the pathogen was called a virus- Latin word meaning “poison.”

3. Virus Terminology
Virus: Segments of nucleic acids held in a protein coat. Are NOT cells; not living, do not grow, no metabolism.
Pathogen: agents that cause disease(s)
Bacteriophage: Viruses that infect bacteria, complex structure.
4. Capsid: Protein coat of a virus; contains DNA or RNA, NOT BOTH!
5. Envelope (Membrane): Surrounds the capsid, allows the virus to enter the cell. Made up of proteins, lipids and glycoproteins. Glycoproteins: proteins that attach carbohydrate molecules.

5. Are Viruses alive?
All living things are made up of cells; cells can grow and reproduce; the smallest organism with “cell-like” properties are prokaryotes.
Viruses are NOT cells, viruses are smaller than prokaryotes. Viruses are pathogens; they CAUSE disease.
How Virus Replicates: Infect cell(s), use the cell to make more viruses.
Viruses need cells because they do not have the properties needed to produce life. (Don’t grow, metabolize and no homeostasis)

6. Structure of Viruses
1. Filaments- Long rods. Example: Ebola virus 2. Spherical- Studded with receptors, allowing the virus to enter the cell. Example: Influenza virus 3. Helical- Rod-like in appearance with capsid proteins winding around the core in a spiral. 4. Polyhedral- Has MANY sides; the capsid of most polyhedral viruses have 20 triangular faces & 12 corners.

7. Viral Reproduction
There are 2 pathways a virus can take in order to replicate itself; Lytic Cycle or Lysogenic Cycle
1. Lytic Cycle
Step 1: Virus attaches to cell, injecting its DNA
Step 2: Viral genes enters the cell
Step 3: Host cell replicates viral genes & viral proteins (A.K.A. Capsid Proteins)
Step 4: Proteins assemble to form a complete virus
Step 5: Host cell bursts open, releasing a NEW virus

8. Lytic Cycle

9. 2. Lysogenic Cycle
Some viruses stay inside a cell, spreading its virus through a cells natural reproduction
Lysogenic cycle allows the viral genes to replicate without destroying the host cell. In some lysogenic viruses, environmental changes can cause the lysogenic cycle to begin.
A virus in the lysogenic cycle can switch to the lytic cycle
Example: Cold sore virus; virus hides in facial nerves. When body conditions are favorable (ie. stress), the virus will cause tissue damage resulting in a cold sore or fever blister

10. Lysogenic Cycle
Step 1: Viral gene is inserted into host chromosome Step 2: Viral genes (DNA or RNA) combines with host DNA Step 3: Host cell divides normally, resulting in 2 new cells, each containing viral DNA. *NO damage to the host cell* * The new cells, containing viral genes, can switch to the Lytic Cycle to create MORE viruses*

11. Lysogenic Cycle

13. Lytic & Lysogenic Cycle Animation 

14. Lytic VS Lysogenic Cycle: Video