VIRUSES

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Chapter 18

• VIRUSES
• BACTERIA

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Microbiology

• Viruses
• Bacteria

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History of Microbiology

• 1668
• Redi disproves spontaneous generation
• 1675
• Leeuwenhoek describes bacteria

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Jenner 1798

• Makes small pox vaccine (1st vaccine) used cowpox
  virus.
• 1818-1865
• Semmelweis Made connection between disease and
  cleanliness.

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PASTURE

• 1860
• Discovered cause of fermentation (yeast)
• Disproved spontaneous generation.

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Pasture

• Organisms can be carried by air.
• Cure for silk worm disease.
• Helped develop resistance for fowl cholera.

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Pasture

• Immunization for Anthrax.
• Rabies Vaccine.

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Koch 1876

• Germ theory of disease.
• Kochs postulates.
• Discovered microbes grow best on a solid in
  colonies.

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Koch 1876

• Developed AGAR.
• Assistant Petri invented the Petri dish.

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Kochs postulates

• 1. Microbe is present in all cases of the
  disease.
• 2. Isolate the microbe and grow in pure culture.

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Kochs postulates

• 3. Pure culture put back into test animal to
  cause the disease.
• 4. Take it out of the 2nd host, isolate and
  identify.

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Lister 1878

• Developed antiseptic surgery.
• Used phenol on everything.

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Beijerinck 1880

• Discovered nitrogen fixing bacteria.
• N2 to NO2

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Iwanowski 1892

• Transferred tobacco mosaic virus into healthy
  tobacco plant, plant became sick.

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Gram 1884

• Developed ways to stain bacteria.
• Gram
• Gram -
• All bacteria fit into these two categories.

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Loeffler Frosch 1898

• Studied Hoof and Mouth Disease.
• Determined that a virus was smaller than a
  bacteria.

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Ehrlich 1910

• After 605 failures discovered Drug 606.
• Used as 1st real drug.
• Used to cure Syphilis.
• Organic Arsenic.

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d Herelle 1917

• Discovered Bacteriophage.
• Agent (virus) that eats bacteria.

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Fleming 1928

• Discovers penicillin from mold.
• One of the greatest medical discoveries of all
  time.
• Kills bacteria.

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Interesting note

• By 1997 some bacteria have evolved to the point
  they are completely immune to ALL antibiotics.

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Stanley 1935

• 1st American to distinguish himself as a
  microbiologist.
• Purified viruses, showed what they were.
• TMV.

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Thomas D. Brock 1966

• Discovers the first Organism living in water that
  is near boiling!
• Names it Thermus aquaticus
• Key to PCR technique.

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Dr. Carl Woese1977

• Proposed that a new Domain be created for extreme
  bacteria.
• Name of Domain Archaea

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What is a Virus???
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Viruses

• A virus is about 1/2 to 1/100th the size of the
  smallest bacterium.
• Most scientists consider them non living.

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Viruses

• Come in many shapes and sizes
• Polyhedral
• Enveloped polyhedral
• Helical
• Enveloped Helical
• Complex

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Why non living?

• Viruses DO NOT exhibit all 7 characteristics of
  life.
• Cells no
• OrganizationYes
• Energy Use.only in host
• Response.Yes

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Alive or Not???

• Growth.Yes in host
• Reproduce.Yes in host
• Adaptation..Yes

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What do viruses do?

• Cause disease
• Influenza
• Aids
• Measles
• shingles
• warts
• colds
• HIV

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What do viruses do?

• Used in Genetic Engineering.

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2 Main Kinds

• Virulent Immediately cause disease.
• Temperate Does not cause disease immediately.

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4 Classes of Viruses

• RNA
• DNA
• Viroids
• Prions

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RNA Viruses

• Nucleic acid is RNA
• Mutate more often than DNA viruses.
• Enter the cell and produce proteins right away
  using hosts ribosomes.

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EXAMPLES

• Polio

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RNA retroviruses

• Use enzyme reverse transcriptase to make DNA from
  RNA.
• New DNA makes new RNA then proteins.

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EXAMPLE

• HIV/AIDS

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DNA viruses

• Once in a cell the DNA makes new RNA and then
  proteins.
• Splices its DNA into a celss DNA then produces
  new proteins.

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EXAMPLES

• Pink-eye

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Viroids

• Short single strand of RNA, free floating.
• Not long enough to make a full protein.
• Usually interferes with normal cell function.

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Prions

• Glycoprotein particle containing about 250 AA.
• Associated w/ diseases that have a long
  incubation period.
• KURU degenerative nerve disease in humans.

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The Bacteriophage
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Anatomy of a Bacteriophage
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The Lytic Cycle

• T2-T4-T6-T8.
• Lytic phages explode host cell to get free.

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Lytic Cycle

• Five phases
• Absorption
• Entry
• Reproduction
• Assembly
• Release

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Absorption

• Virus attacks host.
• Tail fibers contain chemicals that are attracted
  to the surface of the cell.

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Entry

• Virus releases an enzyme that weakens the cell
  wall.
• Tail contracts
• base plate perces the cell wall
• DNA or RNA is injected into the cell

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Replication

• Viral DNA takes complete control of cell
  activity.
• They direct the cell to make viral DNA, proteins,
  and Parts.

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Assembly

• Proteins coded for by viral DNA act as enzymes
  that put the new virus parts together.
• This continues until cell is completely stuffed
  with new viruses.

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Release

• Viruses release an enzyme that digests the host
  cell wall (lysis) allowing the new viruses free
  to start the process over again.

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Lysogenic CycleT1-T3-T5-T7 etc.
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Lysogenic Cycle

• Temperate viruses go though this process.
• DNA injected into cell.
• DNA is incorporated into the host cells DNA
  (prophage).
• Host cell lives normally.

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• Host cell divides, usually many times.
• Each new cell has viral DNA in it now.
• Usually the prophage within each host cell lays
  dorment until triggered by something.

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• Replication
• Assembly
• Release

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