Viruses

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Viruses
Ebola
Influenza
Rabies
HIV
West Nile Virus
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General Characteristics

• 1.Very small
• - 10 -1000 nanometers
• - 10 1000 x 10 -9 m
• - Cannot be seen without an
• electron microscope

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General Characteristics

• 2. Various Shapes

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General Characteristics
Protein Coat

• 3. Structure
• Two Parts
• Nucleic acid
• Protein Coat
• (Capsid)

Nucleic Acid
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General Characteristics

• 4. Acellular
• - no cell
• - no organelles
• - no metabolism
• - cannot be killed with antibiotics

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General Characteristics

• 5. Nucleic acid
• - Has DNA
• - or RNA (retro viruses)
• - (never both)
• ?s 1-6

DNA
RNA
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General Characteristics

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

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General Characteristics

• Nucleic Acids
• 2. RNA ribonucleic acid
• - Single strand
• - Retro virus
• - contains code for directly
• producing viral proteins

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General Characteristics

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

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General Characteristics

• 7. Virus Latin for poison

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General Characteristics

• 8. Obligate intercellular Parasite
• - Cannot reproduce EXCEPT inside
• a host cell
• - No metabolism
• outside host cell
• - Inside host,
• uses cells reproduction
• metabolic mechanisms

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General Characteristics

• 9. Some have an envelope
• Membrane surrounding protein coat
• Made of glycoproteins

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Examples of Viruses

• Common Cold
• Polio
• Rabies
• HIV
• Hepatitis A,B, C
• Herpes ( E.g. Chicken pox)
• Measles
• Smallpox
• ?s 8-13

• Ebola
• Hanta
• HPV (Human papilloma virus)
• Mumps
• Rubella
• Epstein-Barr
• SARS
• can cause cancer

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Viral Cycles

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

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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

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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.
• ?s 7-12

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Lytic vs Lysogenic Cycle
New viruses emerge
Viral DNA
Injection
Bacterial genome
Lysis
Assembly
Many divisions
Synthesis
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How do Viruses do Harm?

• Possible effects
• 1. Lyse cells (Tissue damage)
• 2. Release viral toxins
• 3. Prevent hosts cell division
• 4. Disrupt formation of host chromosomes

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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)

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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)

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Prevention

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

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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 ?s 14-19

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Viroids

1. Nucleic acid (RNA) only
2. No protein coat
3. Common in plants

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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

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Prions

• E.g.
• Kreutzfeld-Jakobs disease
• Bovine Spongiform Encephalopathy
• (BSE) aka Mad cow disease)

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Prions

• 2. Chronic wasting disease
• Deer and elk

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Prions

• 3. Scrapie usually fatal sheep disease

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Prions

• 4. Kuru
• Papua New Guinea
• Headhunters (cannibalistic tribes)

Word to your mama!
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Viruses

• Are they living or nonliving ?
• Are they smart nucleic acids?
• Why cant we kill them?
• ?s 20-25