Monday 4/13/2015
Agenda:
• Activity: Brain Pop
• Notes: Discovery of Viruses
• Activity: Lytic vs. Lysogenic Video
Homework:
• Viral Reproduction Worksheet
due Tuesday/Wednesday 4/144/15/2015 for 40 Points
Week Schedule
• Tuesday 4/14/2015 is a 1,3,5 Block day with lunch
at 10:30 ON CAMPUS
• Wednesday 4/15/2015 is a 2,4,6 Block day with
lunch at 10:30 ON CAMPUS
• Thursday and Friday are block days (1,3,5 and 2,4,6
Friday
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.”
Virus Terminology
1. Virus: Segments of nucleic acids held in a protein coat.
Are NOT cells; not living, do not grow, no metabolism.
2. Pathogen: agents that cause disease(s)
3. 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.
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)
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.
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
Lytic Cycle
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
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*
Lysogenic Cycle
Lytic VS Lysogenic Cycle: Video
• http://www.youtube.com/watch?v=_J9-xKitsd0