Viruses
Why Study Viruses?
ƒ Cause diseases
ƒ Damage living things
ƒ May be fatal
Ebola
Influenza
West Nile Virus
Rabies
HIV
General Characteristics
General Characteristics
2. Various Shapes
1.Very small
- 10 -1000 nanometers
- 10 – 1000 x 10 -9 m
-Need electron microscope
to view
General Characteristics
Protein
Coat
3. Structure =
Two Parts:
Parts:
Nucleic acid
+
Protein Coat
(Capsid)
Nucleic
Acid
General Characteristics
4. Acellular
- no cell
- no organelles
- no metabolism
- cannot be killed with antibiotics
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General Characteristics
General Characteristics
5. Nucleic acid
- Has DNA
ƒ Nucleic Acids
ƒ 1. DNA = deoxyribonucleic acid
- Double strand
- Contains genes for making viral
proteins (requires 2 steps)
- or RNA (retro viruses)
DNA
- (never both)
RNA
General Characteristics
General Characteristics
ƒ Nucleic Acids
2. RNA – ribonucleic acid
- Single strand
- Retro virus
- contains code for directly
producing viral proteins
?s 11-7
6. Mutates very easily
- no cell
- no protection from mutagens
E.g. chemicals, radiation,
uv light exposure
General Characteristics
7. Virus = Latin for poison
Examples of Viruses
Common Cold
Polio
Rabies
HIV
Hepatitis A,B*
A,B*,& C
Herpes ( E.g.
Chicken
pox)
ƒ Measles
ƒ Smallpox
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ Ebola
ƒ Hanta
ƒ HPV (Human
papilloma virus)*
virus)*
ƒ Mumps
ƒ Rubella
ƒ EpsteinEpstein-Barr*
Barr*
ƒ SARS
* can cause cancer
2
Viral Cycles
Lytic Cycle
Two Types of Viral Cycles
1. Lytic
2. Lysogenic
Lysogenic Cycle
™ Viral replication is delayed
1. Viral DNA put into host genome
2. Host cells divide, including viral genes
3. When organism is stressed →
→ lytic cycle begins
→ viral replication (cell lysis)
lysis) etc.
™ Immediate viral replication
1. Injection/InfectionInjection/Infection-Viral DNA into host
cell
2. Synthesis & Assembly of virus
3. Cell lysis (rupture) = tissue damage
4. New viruses emerge to infect new cells
Lytic vs Lysogenic Cycle
New viruses
emerge
Viral
DNA
Bacterial
genome
Injection
Lysis
STRESS
Assembly
Many divisions
Synthesis
How do Viruses Harm You?
Possible effects:
1. Lyse cells (Tissue damage)
2. Release viral toxins (poisons)
3. Prevent host’
host’s cell division
4. Disrupt formation of host
chromosomes
How do Viruses Harm You ?
5. Can cause uncontrolled cell division
(cancer)
6. Can cause changes in cell membrane
(immune system destroys host cells)
?s 88-13
3
Prevention
Vaccines
™ Live or killed virus injected
™ Host immune system makes
antibodies
™ When infected, host immune
system ready to kill virus
Viroids
1.
2.
3.
Nucleic acid (RNA) only
No protein coat
Common in plants
Prions
E.g. Bovine Spongiform Encephalopathy
(BSE – a.k.a. Mad cow disease)
disease)
KreutzfeldKreutzfeld-Jakob’
Jakob’s disease (in humans)
Treatment
1. Antiviral drugs
¾ Interfere with viral replication
¾ E.g. AZT ( for AIDS)
¾ E.g. Interferon (for Hepatitis C)
2. Supportive Therapy
¾ Reduce fever (E.g. aspirin, Tamiflu)
Tamiflu)
¾ Make host comfortable
¾ Wait until virus runs its course ?s 1414-16
Prions
1. Protein only
2. No nucleic acid
3. Replicate by bumping proteins,
causing refolding in shape of
prion
4. Cause diseases of nervous
system
Prions
2. Chronic wasting disease
Deer and elk
4
Prions
3. Scrapie – usually fatal sheep disease
Prions
4. Kuru – destroys human nervous system
Papua New Guinea
Headhunters (cannibalistic tribes)
Word to your
mama!
What are the Modes of
Transmission of a Virus?
How does a virus spread?
1. Direct contact (Touch)
2. Contaminated food, water or body fluids
(e.g. from blood, saliva, or semen)
3. Animal bite (body fluids)
4. Sexual contact (body fluids)
Examples of Modes of
Transmission
Disease
Chicken Pox
Mode of
Transmission
inhalation
Influenza
inhalation
HIV/ AIDS
Contaminated
body fluids
Animal bite
Rabies
Symptoms
Rash, fever
Headache, muscle
aches, sore throat,
cough
Immune system
failure
Madness, death
Viruses
ƒ Are they living or nonliving ?
ƒ Are they smart nucleic acids?
ƒ Why can’
can’t we kill them?
?s 1818-22
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