1. Viruses
Ebola
Influenza
Rabies
HIV
West Nile Virus

2. General Characteristics
1.Very small
nanometers
- 10 – 1000 x m
- Cannot be seen without an
electron microscope

3. General Characteristics
2. Various Shapes

4. General Characteristics
Protein Coat
3. Structure =
Two Parts:
Nucleic acid +
Protein Coat
(Capsid)
Nucleic Acid

5. General Characteristics
4. Acellular
- no cell
- no organelles
- no metabolism
- cannot be killed with antibiotics

6. General Characteristics
5. Nucleic acid
- Has DNA
- or RNA (retro viruses)
- (never both)
DNA
RNA

7. General Characteristics
Nucleic Acids
1. DNA = deoxyribonucleic acid
- Double strand
- Contains genes for making viral
proteins (requires 2 steps)

8. General Characteristics
Nucleic Acids
2. RNA – ribonucleic acid
- Single strand
- Retro virus
- contains code for directly
producing viral proteins

9. General Characteristics
6. Mutates very easily
- no cell
- no protection from mutagens
E.g. chemicals, radiation,
uv light exposure

10. General Characteristics
7. Virus = Latin for poison

11. General Characteristics
8. Obligate intercellular Parasite
- Cannot reproduce EXCEPT inside
a host cell
- No metabolism
outside host cell
- Inside host,
uses cell’s reproduction
& metabolic mechanisms

12. General Characteristics
9. Some have an envelope
Membrane surrounding protein coat
Made of glycoproteins

13. Examples of Viruses Ebola Hanta HPV (Human papilloma virus)* Mumps
Common Cold
Polio
Rabies
HIV
Hepatitis A,B*,& C
Herpes ( E.g. Chicken pox)
Measles
Smallpox
Ebola
Hanta
HPV (Human papilloma virus)*
Mumps
Rubella
Epstein-Barr*
SARS
* can cause cancer

14. Viral Cycles
Two Types of Viral Cycles
1. Lytic
2. Lysogenic

15. Lytic Cycle Immediate viral replication
Viral DNA injected into host cell
Viral DNA put into host genome
Synthesis & Assembly of virus
Cell lysis (rupture) = tissue damage
New viruses emerge to infect new cells

16. Lysogenic Cycle Viral replication is delayed
Viral DNA put into host genome
Host cells divide, including viral genes
3. When organism is stressed →
→ lytic cycle begins
→ viral replication (cell lysis) etc.

17. Lytic vs Lysogenic Cycle
New viruses emerge
Injection
Viral DNA
STRESS
Bacterial genome
Lysis
Assembly
Many divisions
Synthesis

18. How do Viruses do Harm? Possible effects: Lyse cells (Tissue damage)
Release viral toxins
Prevent host’s cell division
Disrupt formation of host chromosomes

19. How do Viruses do Harm? 5. Disrupt lysosomal function
6. Can cause uncontrolled cell division (cancer)
7. Can cause changes in cell membrane
(immune system destroys host cells)

20. Duration of Viral Infections
Acute – rapid onset, death or recovery
(most viruses)
Chronic – recurs again & again
- latent period = virus dormant between flare-ups
E.g. Herpes simplex
(cold sores)

21. Prevention Vaccines Live or killed virus injected
Host immune system makes antibodies
When infected, host immune system ready to kill virus

22. Treatment Antiviral drugs Interfere with viral replication
E.g. AZT ( for AIDS)
E.g. Interferon (for Hepatitis C)
2. Supportive Therapy
Reduce fever (E.g. aspirin, Tamiflu)
Make host comfortable
Wait until virus runs its course

23. Viroids
Nucleic acid (RNA) only
No protein coat
Common in plants

24. Prions Protein only No nucleic acid
Replicate by bumping proteins, causing refolding in shape of prion
Cause diseases of nervous system

25. Prions E.g. Kreutzfeld-Jakob’s disease
Bovine Spongiform Encephalopathy
(BSE) aka Mad cow disease)

26. Prions
2. Chronic wasting disease
Deer and elk

27. Prions
3. Scrapie – usually fatal sheep disease

28. Prions 4. Kuru Papua New Guinea Headhunters (cannibalistic tribes)
Word to your mama!

29. Viruses Are they living or nonliving ? Are they smart nucleic acids?
Why can’t we kill them?