Transcript Viruses have been called the greatest threat to the survival of

Why are viruses
dangerous?
Host
Lysogenic
Cycle
Parasitic
Relationships
Viruses
Lytic
Cycle
Shapes of
Viruses
Viruses
• Not cells b/c no cytoplasm or organelles.
• Basic structure is some form of genetic
material in a protein coat.
• Invades a cell and destroys it
Viruses Cont.
• Found everywhere
Ex. 5 billion in 1 drop of blood.
• Ever changing
Ex. Colds, flu, and AIDS
What do viruses look like?
Virus Shapes
Crystals
Ex. Polio virus
Spheres
Ex. Influenza and
HIV virus
Virus Shapes Cont.
Cylinders
• Tobacco Mosaic
virus
Spacecraft
• Attacks only
bacteria.
How do viruses survive in the
environment?
Host
• Viruses don’t eat, grow, breathe, or perform
biological functions.
• Viruses reproduce inside a host cell.
• Viruses have parasitic relationships.
• They reprogram the cell.
So, how does the virus get
inside the host? And, what does
it do there?
Reproduce!
The Lytic Cycle
1. The virus finds a host.
2. Enters the cell or genes are injected.
3. Genes reprogram the host cell into a virus
“factory”.
4. New viruses break out to find a new host
cell.
Lysogenic Cycle
• Inactive virus genes that wait inside the cell until
after the host cell divides.
• Changes in environment and stress can cause
the virus to become active.
Immune System
• White blood cells attack and engulf
anything that is not suppose to be in the
body.
• A “plan of attack” is kept in
the body in case you get the
same virus again.
Ex. Killer T Cells and
Helper B Cells
Vaccines
• Edward Jenner developed the first vaccine
in the late 1700’s. It was for small pox.
• A vaccine is a weakened or inactive virus
used to develop immunity against viruses.
Explain why virus are so dangerous. Use
terms and concepts we discussed in class
today.