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1. What is a virus?
A microscopic particle that can get inside a cell and often destroy it.
2. How big is a virus?
Tiny
Smaller than a bacterial cell.
5 billion can fit in one drop of blood.
*Enlarged 600,000 times a virus would be the size of a pea. If you were
enlarged 600,000 times, you would be about 3 million feet tall.
3. Are viruses alive?
NO!
They don’t eat, they don’t grow, they don’t reproduce unless they are inside
a host, they don’t use oxygen.
Viruses are like living things because they contain protein and nucleic acid
(DNA) and they can adapt to be better at infecting cells.
Characteristics that make it seem:
Alive
Can invade a cell and use the cell’s
organelles
Contains nucleic acid (DNA or
RNA)
Reproduces (ONLY inside the host
cell)
Non-living
Has no cell organelles
Does not move
Does not grow
Can become latent (inactive) for
years
4. Parts of a Virus:
1. The protein coat aka capsid.
*** allows the virus to recognize and attach to a host cell.
2. The nucleic acid (contains directions for reproducing the virus). Can
be DNA or RNA.
5. How are viruses classified?
Classification:
 Based on the diseases they cause
 Based on shape:
o Rod like, usually infect plants (Tobacco Mosaic Virus)
o Crystal like (ex: polio)
o Spherical, influenza, HIV
o Spacecraft, infect bacterial cells
6. What is the LYTIC Cycle:
The active phase of a virus’ life.
The virus is making 1,000’s of new virus particle using the cell’s organelles.
FOUR steps:
1. Attaching to the host cell.
2. Injecting the viral DNA into host.
3. Reproducing and making more virus particles
4. Host cell bursts and releases new virus particles
7. Viruses have two parts to their lifecycle:
1. Lytic Cycle (Active Cycle): Virus infects and HIJACKS the host cell.
Cell is turned in to a VIRUS FACTORY and makes more virus.
2. Resting Cycle (Lysogenic Cycle): Virus gets into the host’s DNA and
just stays there.
When cell divides, virus DNA gets copied too
***Stress and other factors cause a virus to go from resting to lytic.
8. How are viruses treated?
Cannot be cured.
Antibiotics can’t treat them.
Can treat symptoms (like runny nose, cough, headache)
CAN get a vaccine that teaches your body to fight the virus and help you not
get sick.
Viruses:
Herpes virus causes cold sores
HPV
Influenza
HIV
Chicken Pox (varicella zoster)