Viruses _ Bacteria by wulinqing


									Viruses &
Chapter 19.2   Herpes virus   Ebola virus
Slide # 2

                Discovery of Viruses
      1.    In Russia, Dmitri Ivanovsky was asked to
            investigate a disease affecting tobacco plants.
      2.    He found juice from one plant infected other
            plants, even when passed through fine filters.
      3.    He found no cells in this “juice” and concluded
            that the disease was caused by a “poison”.
      4.    Later it was suggested that the infecting agent
            was a very tiny particle.
      5.    One scientists isolated virus crystals inferring
            that these virus particles were not living.
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            How Small is a Virus?
Slide # 4

            Viruses are 1/1000 to 1/10,000
                 the size of our cells.
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            What is a Virus? Latin for poison
       1. contain DNA or RNA
       2. are not cells
       3. are non-living particles
       4. do not have a
       5. can not reproduce on
          their own (-the infected
          host cell reproduces
          the virus particles)
       6. are parasites that can
          cause disease
Slide # 5
Slide # 7

            How are Viruses Classified?
     1. Type of nucleic acid:
        DNA or RNA
     2. Shape of Protein Coat
        (called a Capsid)

 Cold virus    Tobacco       Flu virus    Bacteriophage virus
              Mosaic Virus
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  3. Retrovirus
  a. Class of RNA viruses
            that changes its RNA
            into DNA when
            injected into a host
  b. Contains reverse
  c. Example of a
            Retrovirus is HIV the
            virus that causes
Slide # 9

                 How do Viruses Work?
     1.      Viruses use a host cell to reproduce: The virus
             must inject their genetic material into a host
             cell, so it can instruct the host cell to make new
             virus particles.

     2.       Viruses are specific to the type of cell it can
                Ex. The Hepatitis virus only infects liver cells.
                Ex. HIV only affects Helper T cells (type of
                 immune system cell)
                Ex. A bacteriophage virus…
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Ex. A Bacteriophage virus only infects   BACTERIA.


    E. coli

Bacteria are destroyed as viruses break out.
Slide # 11

 Empty capsids litter this infected bacterium’s cell wall.

                                          Where is the
                                          viral genetic
                 Viral Capsids            inside the
                 (protein coat)           bacteria
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 3.A Virus is specific in the type of cell it invades
   because it attaches to specific binding sites
   called Receptors on the host cell.

             Virus                 Receptors on the
                                   host cell have a
                                   similar shape to the

Slide # 13

       Hijacking a Host Cell to Reproduce
         1.    The virus attaches to a receptor on the host
         2.    Genetic info is inserted into the host cell.
         3.    Host Cell is forced to make virus genetic
               material (DNA or RNA) and proteins (capsid).
         4.    Viruses are assembled (put together).
         5.    New virus particles break out of the host cell
               killing it.
              *(Some viruses bud out without destroying the
               host cell. -ex. HIV)
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                        Lytic Cycle:

             Viral reproduction occurs
             immediately and host cell death in
             most cases.

       Animation Link
Slide # 15

                                Viral Reproduction: The Lytic Cycle
                                            Bacteriophage             Bacteriophage DNA
                                            protein coat

                                                  Bacteriophage attaches to
                                                  bacterium’s cell wall

             Bacteriophage enzyme lyses the
             bacterium’s cell wall, releasing
             new bacteriophage particles that        Lytic Cycle
             can attack other cells.
                                                                                     Bacteriophage injects
                                                                                     DNA into bacterium

               Bacteriophage proteins
               and nucleic acids
               assemble into complete       Bacteriophage takes over
                                                                                           Bacteriophage DNA
               bacteriophage particles      bacterium’s metabolism,
                                                                                           Bacteriophage protein
                                            causing synthesis of new
                                            bacteriophage proteins and
                                            nucleic acids

Go to
Slide # 16

                       Lysogenic Cycle:
      Animation Link

      • Viral DNA hides out by inserting itself
        into the host DNA.
      • Prophage (or Provirus): viral DNA
        that has been inserted into the host’s
      • It may lay dormant (inactive) for a
       period of time or it may periodically
       release a few viruses (switches to
       lytic cycle).
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                                The Lysogenic Cycle
                   Bacteriophage                  Bacterial
                   DNA                            chromosome

                                   Bacteriophage                Bacteriophage DNA
                                   injects DNA into             (prophage) can exit the
                                   bacterium                    bacterial chromosome

                                        Lytic                        Lysogenic
                                        Cycle                        Cycle
                                                Bacteriophage DNA
      Bacteriophage enzyme lyses                                                 Bacteriophage DNA
                                                forms a circle
      the bacterium’s cell wall,                                                 (prophage) may replicate
      releasing new bacteriophage                                   Prophage     with bacterium for many
      particles that can attack other                                            generations

                                 Bacteriophage proteins        Bacteriophage DNA inserts
                                 and nucleic acids             itself into bacterial
                                 assemble into complete        chromosome
                                 bacteriophage particles
Go to
Lytic and Lysogenic Cycles of Reproduction

                                  Pg. 481
 Mysterious  Invaders
 Virus Information and pictures
 Lytic Cycle Animation
 Can you get AIDS from a mosquito bite?
 HIV Infection animation

                     The HIV Virus

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