Viruses
What is a virus?
Non Living
Microscopic organism
Need host cell to reproduce (hijacks the cell and has it make more viruses)
What is a virus made of?
Made of DNA or RNA and a capsid (coat made of protein)
Many contain an envelope (membrane surrounding the capsid) which helps them enter cells
The capsid is made of protein, lipid and glycoproteins (protein + carbohydrate molecule)
How do viruses spread?
Person to person or Mother to child
Contact, exchange of saliva/coughing/sneezing, contaminated food/water, insects (Endocytosis)
Remember: Bacteriophages! (Virus that infects bacteria)
Lytic Cycle:
(1) Virus attaches to a cell and injects DNA
(2) viral DNA enters the lytic cycle
(3) new virus is made
(4) cell breaks open and releases viruses
Lysogenic Cycle:
(1) Virus attaches to a cell and injects DNA
(2) viral DNA enters the lysogenic cycle
(3) Viral DNA integrates with host DNA
(4) Host cell divides normally
(5) virus may enter lytic cycle
**single virus that infects a bacterial cell can produce 100 new viruses in 20 minutes**
Diseases caused by viruses
Common cold, smallpox, measles, chickenpox, flu, HPV, polio, HIV, herpes, Epstein-Barr (mono)
Tobacco Mosaic Virus
How do we fight viruses?
Healthy immune system, skin integrity, hand washing
Sometimes we vaccinate (flu or smallpox)
Sometimes we can give anti-viral medication
Smallpox disease was eliminated in 1970’s after an effort to inoculate every man, woman, and child in
the world. Two collections of frozen smallpox virus have been preserved, one in Atlanta and the other in
Moscow. Why? Research in case of bioterrorism
Prions and Viroids
Prion: 1982 – described by Stanley Prusiner at Stanford University
Made of protein, but have no nucleic acid.
Disease causing prions are folded in a way that doesn’t allow the protein to function, contact
with normal proteins causes them to misfold and stop functioning. (Chain reaction)
(1) Scrapie – sheep
(2) Mad Cow Disease – cow
(3) Creutzfeldt-Jakob disease – humans
Viriod: single strand of RNA with no capsid
Important infectious disease agents in plants (cucumbers, oranges, potatoes, avocado)