Chapter 6 Review

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Anonymous
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7285
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Chapter 6 Review
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2010-02-18 11:51:59
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Microbiology chapter6 viruses
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Review chapter 6
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  1. Type of Viruses
    • - Naked nucleocapsid virus
    • - nucleicacid
    • - capsid

    • - Envelope Virus
    • - nucleic acid
    • -capsid
    • -envelope
    • -spikes
  2. What are Viruses?
    - unique group of biological entities known to infect every type of cell

    • - unusual structure and behavior
    • - all possess a protein capsid surrounding some type of nucleic acid

    - infectious particles

    - obligate intracelluar parasites
  3. What is a capsid?
    • - protective outer shell that surrounds viral nucleic acid
    • - capsid spikes are used for attachement to host cells
    • - composed of capsomer subunits
    • - two types of capsids
    • - helical
    • - icosahedral
  4. Helical Capsid
    • - rod-shaped capsomers bond forming a hollow disc similar to a bracelet
    • - form a continuous helix
    • - nucleic acid coils inside
  5. Types of Helical Viruses
    • - naked helical virus
    • - tobacco virus
    • - nucleocapsid is rigid and tightly wound into a cylinder-shaped package

    • - Enveloped helical virus
    • - influenza, measles, rabies
    • - nucleocapsid is more flexible
    • - envelope comes from host cell membrane
  6. Icosahedron capsid
    - three dimensional, 20 sided with 12 evenly spaced corners

    • - variation in capsomer numbers
    • - polio virus 32 capsomers
    • - adenovirus 240 capsomers
  7. Types of Icosahedral Viruses
    • - naked icosahedral viruses
    • - papillomavirus

    • - Enveloped icosahedral viruses
    • - herpesvirus
    • - envelope comes from host cell membrane
  8. Envelope
    • - most common among animal viruses
    • - lipid and proteins
    • - during release of animal viruses, a part of the host membrane is taken

    • - has envelope spikes for attachment of viruses to the next host cell
    • - enable pleomorphic shape of the viruses
  9. Function of Capsid/Envelope
    - protect nucleic acid from the host's acid and protein digesting enzymes

    - assist in binding and penetrating host cell

    - stimulate the host's immune system
  10. Complex Viruses
    • - intricate structure
    • - pox virus
    • - several layers of lipoproteins
    • - course surface fibrils

    • - bacteriophage
    • - polydedral head
    • - helical tail
    • - fibers for attachment
  11. Nucleic Acid
    - viruses contain either DNA or RNA but not both

    - possess only the genes to invade and regulate the metabolic activity of host cells

    - no viral metabolic genes; the virus uses the host's metabolic resources
  12. Clinically important DNA viruses
    • DNA viruses:
    • - Enveloped
    • - double stranded genome

    • - Non-enveloped
    • - single stranded genome
    • - double stranded genome
  13. Clinically Important RNA Viruses
    • RNA Viruses:
    • - enveloped - non-enveloped
    • - single stranded genome - single stranded genome
    • - segmented genome - double stranded genome
    • - non segmented genome
  14. Multiplication Cycle
    • - adsorption (attachment)
    • - penetration/uncoating
    • - synthesis
    • - assembly
    • - release
  15. Adsorption
    • - viral attachment to host cell is mediated by spike proteins
    • - spikes recognize only certain host receptors
    • - basis for specificity
  16. Viral Penetration/ Uncoating
    • - naked viruses are endocytosed
    • - requires degradation of cell membrane and capsid prior to uncoating

    • -enveloped viruses
    • - viral envelope fuses to host cell membrane
    • - allows only capsid to directly enter cytosol
  17. Release of Enveloped Viruses
    • - liberated by budding or exocytosis
    • - allows them to retain a portion of the host cell membrane
  18. Cytopathic Effects
    • - Damage to the host cell due to a viral infection
    • - inclusion bodies: compact masses of viruses of damaged cellular material
    • - syncytia: fusion of multiple host cells into a single, large, multinucleated cell
    • - chronic latent state: viruses remain dormant in a certain cell type periodically becoming reactivated
    • - transformation: viral geneic material permanently alter host genome
    • - oncogenes
  19. Bacteriophage
    • - virus that specifically infects bacteria
    • - multiplication is similar to animal viruses except:
    • - pentration occurs via injecting DNA
    • - can form a dormant prophage (lysongeny)
    • - release (lyses) destroys the cell
  20. Viral Release
    - viral enzymes weaken host cell membrane

    - leads to rupture the cell (lyses)

    - release numerous virions
  21. Lysogeny
    - insertion of viral DNA into the bacterial host genome

    - allows viral DNA to be copied with every cell division of bacteria
  22. Cultivating Animal Viruses
    - eggs provide an intact, self-supporting unit for viral maintenance

    - viruses can be injected through shell into various areas within embryonic egg
  23. Normal Versus Infected Cells
    • - tissues are grown on culture media
    • - normal cells form an even monolayer of undisturbed cells

    - viruses cause an aggregation of cells forming visible plaques
  24. Non cellular Infectious Agents
    - prions

    - satellite viruses

    - viroids
  25. What are Prions?
    - protein particle with no nucleic acid, no envelope, no capsid

    • - Diseases
    • - creutzfeldt- Jakob
    • - "mad cow disease"
  26. Satellite Viruses
    • - dependent on other viruses for replication
    • - delta agent: naked RNA only expressed in the presence of hepatitis B virus potentially worsening the damage to liver cells
  27. Virods
    • - plant pathogens
    • - tomatoes, potatoes, cucumbers

    - 1/10th the size of normal viruses

    - naked strands of RNA, no capsid

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