Chap. 24:Viruses

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Chap. 24Viruses

• Ex. Cold, polio, rabies, herpes, AIDS, small pox,
  flu, cancers, mono, chicken pox, HPV, Ebola,
  SARS, West Nile, Mad-Cows Disease, etc.

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I. Terminology

• Virology study of viruses
• Virulent when a virus causes a disease
• Temperate when a virus doesnt cause disease
  right away (AIDS, cancer)
• Obligate intracellular parasite (virus) must
  use a host for reproducing
• Nanometer (nm) measurement for virus. 4000 can
  fit within a typed o

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- Viroid smaller than a virus contains only a
single strand of RNA

• Prion contains about 250 amino acids no
  nucleic acid. Causes long term diseases like
  Kuru.
• Bacteriophage virus that attacks bacteria (also
  called phages)
• Oncogenes genes that cause abnormal cell growth
  (tumors, aka cancer)
• II. Structure
• - classified by either having DNA or RNA not
  by binomial nomenclature.

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-- RNA viruses contain reverse transcriptase an
enzyme that changes RNA to DNA called
retroviruses.
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III. Viral Cycles

• 1. Lysogenic Cycles
• a. Tail fibers attach to cell
• b. Nucleic acid injected into host
• c. Nucleic acid attaches to host nucleic acid
  to become a prophage
• d. Doesnt cause harm immediately but at some
  point it can become the lytic cycle.
• e. Causes transduction (spreading of new DNA to
  another cell) ex. Cancers,cold sores,shingles,
  AIDS

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2. Lytic Cycle immediate taking over of a host
cell.

• Attachment virus attaches tail fibers down onto
  host cell membrane.
• Entry DNA/RNA is injected into cell.
• Replication viral DNA/RNA tells host cell to
  make more viruses
• Assembly making of more viruses
• Lysis (release) host cell ruptures and releases
  all viruses to go and infect new cells.
• -- interferon chemical released by host cell
  upon rupture to signal neighboring cells of virus

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IV. Transmitting of viruses

• Vector organism that transmits a virus
  usually an arthropod (insect) ex. Tick, mosquito,
  flea
• Viral reservoir place where virus originated
• --- viruses are transmitted by air, exchange
  of body fluids, direct contact, water

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A. Viral Control

• 1. vaccination given inactivated (dead or
  diluted amount) or attenuated (genetically
  altered) virus.
• ---- Result Antibodies made by body to
  recognize and destroy virus
• 2. Antiviral drugs drugs that interfere with
  viral making. Ex. AZT for AIDS

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Antibiotics do not work on viruses because
they are made to target the cell processes of a
bacteria

• Pandemic when a disease spreads across the
  world. Ex. AIDS
• Endemic disease isolated to a specifc region.
  Ex. Ebola
• Epidemic rapid spreading of a disease and
  affecting many. Ex. Influenza 1918