micro exam 3 part 1

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micro exam 3 part 1
2011-07-07 15:06:39
micro exam part

micro exam 3 part 1 Q&A
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    - The type of active immunity that develops when an individual’s immunologic system comes into contact with an appropriate antigenic stimulus arises as the result of recovering from an infection and last a long time.
    The type of temporary immunity that involves the transfer of antibodies from one individual to another
    The type of immunity that results from immunizing an animal with a vaccine. The immunized animal now produces its own antibodies and activated lymphocytes.
    The type of immunity that results from introducing into animal antibodies that have been produced either in another animal or by in vitro methods. Immunity is only temporary.
  5. What did Beijerinck do?
    Published results of tobacco mosaic disease. He filtered sap of diseased plants and it was still infectious, he proposed that the disease was caused by an entity different that bacteria. He called them filterable viruses. He observed that the virus would multiply only in living plant cells, but could survive for long periods of time in a dried state..
  6. What did d'Herelle do?
    Discovered bacterial viruses and named them bactriophages. He proposed that bacteriophages could be used to treat bacterial diseases. He discovered the existence of bacterial viruses when he isolated them from patients with dysentery.He also developed a procedure for enumerating them called a plaque assay. He demonstrated that bacterial viruses could only reproduce in live bacteria.
  7. What are viruses? Characteristics?
    Simple, acellular infectious agent, Virions contain either RNA or DNA, but not both, and are obligate intracellular parasites because they can only reproduce inside of a living host cell.
  8. What type of nucleic acids (NA) are carried by viruses?
    DNA or RNA.
  9. What is Plaque Assay used for?
    Several dilutions of viruses are plated out with appropriate host cells. This will allow a proper count of infectious virions and the concentration of infectious units.
  10. What is the size range of a viron?
    Size ranges from 10nm to 400nm.
  11. What is the difference in the way virus are grown from bacteria?
    Bacterial and archaeal viruses are usually cultivated in broth or agar cultures of suitable, young, actively growing host cells and in some infected cultures so many host cells are destroyed that the turbidy of culture quickly turns clear because of cell lysis. Agar cultures are prepared by mixing viruses with cool, liquid agar and a suitable culture of host cells. The mixture is poured in a Petri dish with a layer of sterile agar on the bottom. Once it hardens cells in the layer of the top agar grow and reproduce forming a continuous opaque layer or lawn. When a virion comes to rest in the top agarthe virus infects an adjacent cell and reproduces and eventually lysis of the cells generates a plaque or clearing in the lawn
  12. How are animal viruses cultured?
    By inoculating suitable host animals or embryonated eggs.
  13. What is the function of a viral protein coat?
    Protects viral genetic material and aids in its transfer between host cells
  14. What are viral envelopes composed of?
    A lipid layer external to the nucleocapsid.
  15. What are the characteristics of viral envelopes?
    They are either helical (hollow tubes with protein walls), icosahedral (triangular faces and vertices), or Complex symmetry( ovoid or brick shaped exterior. Animal virus envelopes usually arise from host cell nuclear or plasma membrane. Their lipid and carbohydrates are normal host constituents. The envelope is flexible, membranous structure and are sometimes called pleomorphic, but sometime such as the bullet shaped rabies, the envelope is firmly attached to the underlying nucleocapsid.
  16. Describe differential centrifugation.
    Separates viruses according to size. The centrifugation of a suspension at various speeds to separate particles of different sizes.
  17. Describe gradient density centrifugation.
    Separates according to buoyant density of to sedimentation rate (size and density), and is more sensitive to small differences among various viruses.
  18. Describe self-assembly process.
    The spontaneous formation of a complex structure from its component molecules without the aid of special enzymes or factors.
  19. What criteria are used to classify animal viruses?
    • 1. Nucleic acid type
    • 2. Nuecleic acid strandedness (double or single stranded)
    • 3. The sense of ssRNA genomes
    • 4. The presence of absence of an envelope
    • 5. The host
  20. What mechanisms do viruses use to cause cancer?
    • 1. Viruses may carry one or more cancer-causing genes (Oncogenes)
    • 2. Viruses may produce a regulatory protein that activates cell division
    • 3. Viruses may insert a promoter or enhancer nest to a cellular proto-oncogene (a cellular gene that regulates cell growth and reproduction), causing abnormal expression of this gene and therby deregulating cell growth.
    • 4. Viruses may inhabit the activity of tumor suppressors that regulate cell cycling.
  21. What virus has been associated with a form of liver cancer?
    Hepatitis B virus.