Viruses

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Viruses
Not alive, not dead, non cellular, must enter a
host cell to reproduce
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Comparing the size of a virus, a bacterium, and a
eukaryotic cell
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Figure 18.2 Viral structure
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Adenovirus some respiratory infections
Minimum structure to a virus protein
coat/capsid, nucleic acid
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Figure 18.3 A simplified viral reproductive cycle
Simplified viral life cycle host becomes
virus factory
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Life cycle of an envelope virus - envelope
stays outside
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HIV, a retrovirus contains RNA and must
replicate backwards to DNA
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HIV infection virus attaches to receptors on
cell membrane. Cell drags in the virus
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AIDS quilt
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Viral diseases

• Link between infection symptoms varies
• kill cells by lysis inflammation, pain,
  swelling
• cause infected cell to produce toxins
• viral components, such as envelope proteins, may
  be toxic and cause an immune response fever,
  swollen glands etc.
• Damage?
• depends
• lung epithelium after the flu is repaired
• nerve cell damage from polio is permanent

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Smallpox dsDNA virus
Eradicated in 1976 Vaccinations ceased in 1980
Are we an at risk population?
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Measles Virus ssRNA acts as template for mRNA
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Polio attacks nerve cells and destroys them
ssRNA virus
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Hepatitis B linked to liver cancer
Transmitted by infected blood and body fluids
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Influenza epidemic 1918 30-40 million deaths
worldwide
RNA virus
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Emerging Viruses

• Viruses that mutate jump host
• Hanta virus
• Ebola virus
• digests human body every opening in body
  bleeds, no matter how small
• - Avian flu may jump from birds to humans

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Emerging viruses
Ebola Virus causes hemorrhagic
fever Transmitted by infected Blood/boy fluids,
not airborne
Hanta Virus transmitted from rodents by
airborne particles from fecal matter
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Lytic and Lysogenic cycles

• Lytic cycle virus causes host cell to lyse/
  rupture
• Lysogenic cycle virus integrates its nucleic
  acid into the host cell genome. Viral nucleic
  acid is reproduced when cell does mitosis. Virus
  may become lytic later

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Phages
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The lytic cycle of phage T4 ( causes cells to
lyse)
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Figure 18.5 The lysogenic and lytic reproductive
cycles of phage ?, a temperate phage
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Figure 18.x6 Herpes a lysogenic virus that
becomes lytic
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Figure 18.9 Viral infection of plants
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Figure 18.9x Tobacco mosaic virus first virus
discovered
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Prion Diseases

• Public Service Announcement
• How to determine if your cow has mad cow
  disease...

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Normal polypeptide misfolded
polypeptide prion
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Figure 18.10 A hypothesis to explain how prions
propagatePrions are small misfolded
polypepetides that create adomino effect of
misfolding.
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• Bovine Spongiform Encephalopathy
• Mad Cow Disease
• caused by a prion or something causes the prion
• to be present in high amounts in infected
  individuals
• causes fatal brain disorder
• variant is Creutzfeldt Jakob Disease (CJD)
• Chronic Wasting Disease in elk, deer
• prions survive, cooking, freezing and
  incineration

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Bacterial geneticshelps us with biotechnology

• Bacterial industries leather tanning, dairy
  products, sauerkraut, pickles, composting,
  recombinant bacteria make human insulin and HGF (
  human growth factor ), snow making, clean up oil
  spills

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Bacterial genetics

• Bacterial chromosome is circular and there is
  one/ cell. May also contain plasmids small DNA
  loops.
• no mRNA processing ( no introns)
• DNA replicates when cells divide ( binary fission
  ( no IPMAT ) Cells can divide every 20 minutes
• Transformation bacteria pick up DNA from their
  environment
• Transduction bacteria get viral genes when
  bacterium is infected by virus
• Conjugation sexual exchange of DNA between
  bacteria
• 3 ways bacteria can genetically change

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Figure 18.11 Replication of the bacterial
chromosome
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Figure 18.x7 E. coli
Binary fission every 20 minutes under the right
conditions. What do think are the right
conditions for bacterial growth?
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Figure 18.x9 Bacterium releasing DNA with
plasmids
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Figure 18.x10 Plasmids separate loops of DNA
that may carry extra genes. Aplasmid is not a
circular bacterial chromosome