1. Viruses
Chapter 19

2. What you must know: The components of a virus.
The differences between lytic and lysogenic cycles.
How viruses can introduce genetic variation into host organisms.
Mechanisms that introduce genetic variation into viral populations.

3. Bacteria vs. Viruses Bacteria Virus _________________ cell
Most are free-living (some parasitic)
Relatively ________ size
__________________ used to kill bacteria
Not a living cell (_________ packaged in __________ shell)
Intracellular parasite
1/1000 size of bacteria
______________ used to prevent viral infection
Antiviral treatment

4. Viruses Very small (<ribosomes) Components = ____________+ ________
Nucleic acid: DNA or RNA (__________ or __________ -stranded)
_____________: protein shell
Some viruses also have viral _______________ that surround capsid

5. Viruses Limited ________ range
Entry = attach to host cell membrane receptors through capsid proteins or glycoproteins on viral envelope (animal)
Eg. human cold virus (rhinovirus)  upper respiratory tract (mouth & nose)
_______________ quickly within host cells
Can ___________ easily
RNA viruses: no error-checking mechanisms

9. Simplified viral replicative cycle

10. Viral Reproduction Lytic Cycle:
Use host machinery to replicate, assemble, and ___________________________of virus
Virulent phages: Cells die through lysis or apoptosis
_________________ (Latent) Cycle:
DNA incorporated into host DNA and replicated along with it
Bacteriophage DNA = prophage
Animal virus DNA = provirus
UV radiation, chemicals can stimulate: lysogenic  lytic cycle
Temperate Phage: uses both methods of replication

11. Bacteriophage
Virus that infects _____________ cells

12. Lytic Cycle vs. Lysogenic Cycle

13. Animal viruses have a membranous ___________
Host membrane forms around exiting virus
Difficult for host immune system to detect virus

14. Retrovirus RNA virus that uses ___________________ (RNA  DNA)
Newly made viral DNA inserted into chromosome of host (provirus)
Host transcribes provirus to make new virus parts
Example: ___ (Human Immunodeficiency Virus)

15. HIV = Retrovirus

16. HIV Origin: Chimpanzee virus
Infects white blood cells (_________________)
_______: provirus (DNA inserted), latent
_______: <200 WBC count, opportunistic infections

17. Other Human Viruses __________ virus ______________
Herpes Simplex Virus 1 (HSV-1)
Herpes Simplex Virus 2 (HSV-2)
Eradicated in 1979 due to worldwide vaccination campaigns

18. Emerging Viruses = mutation of existing viruses Pandemic: ____________ epidemic

19. Current Outbreaks ___________ Virus Dengue Fever Chikungunya
Spread by Aedes mosquitoes (Aedes aegypti)
Major outbreak in Brazil and Latin America
Linked to birth defects (microcephaly)
Dengue Fever
Chikungunya

20. Drugs for Prevention/Treatment
______________: weakened virus or part of pathogen that triggers immune system response to prevent infection
Ex. HPV, MMR, HepA, Flu shot
________________ Drugs: block viral replication after infection
Ex. Tamiflu (influenza), AZT (HIV)

21. Viroids Small, circular _________ molecules that infect __________
Cause errors in regulatory systems that control plant growth
Eg. coconut palms in Philippines

22. Prions
Misfolded, infectious ______________ that cause misfolding of normal proteins
Eg. scrapie (sheep), mad cow disease (BSE), Creutzfeldt-Jakob disease (humans), kuru (humans – New Guinea)

23. Diseases caused by prions
Prions act slowly – incubation period of at least 10 years before symptoms develop
Prions are virtually indestructible (cannot be denatured by heating)
No known cure for prion diseases
Kuru in New Guinea

24. Prion Neurodegenerative Diseases
Alzheimer’s Disease
Parkinson’s Disease