VIRUSES

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VIRUSES
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Characteristics of Viruses

• Tiny, non-living particles
• Do not respire, move or grow
• Cannot reproduce on their own
• Must reproduce inside of a host cell
• Typical infection 7-10 days
• Not given Latin names
• named for disease caused
• organ infected
• region detected

Draw Fig. 19-13 page 483
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Virus Structure

• All viruses 2 basic parts
• nucleic acid
• protein coat (capsid)
• Capsid protein coat containing inner core of
  DNA or RNA
• Protein coat gives viruses diff. shapes
• Polyhedral
• Cylindrical
• round, etc.
• May have tail fibers and projections to aid in
  attachment
• Some have extra outer layer called Envelope

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Viral Recognition Attachment

• Virus must recognize specific receptor site on
  host cell
• Lands on host and locks in
• Attachment is specific
• virus can enter and reproduce in only a few types
  of cells
• Ex Tobacco Mosaic Virus cannot affect human
  cells even though we are exposed to it daily

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Viral Reproduction.

• Viruses must reproduce inside of a host cell
• They are classified as Intracellular Parasites
• The method of entry into the host cell depends on
  the virus
• There are two main types of viral reproduction
• Lytic cycle
• Lysogenic cycle

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Steps of the Lytic Cycle

1. ATTACHMENT Bacteriophage attaches to the cell
   surface of a bacterium

2. PENETRATIONDNA enters bacterial cell
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3. REPLICATIONBacteriophage is replicated
proteins are synthesized 4. ASSEMBLYPhage
components are assembled into mature viruses
5. RELEASE/LYSESBacterial cell lyses releases
many phages that can now infect other cells
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Lysogenic Cycle

• Viruses attack cells
• Do not kill cell immediately
• Viral DNA is mixed with host DNA
• Does not immediately begin to reproduce
• Host cellmay function normally while virus
  staysdormant
• Example Herpes (cold sores, fever blisters)

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1. ATTACHMENTPhage attaches to cell surface of
   bacterium
2. PENETRATIONPhage DNA enters the bacterial
   cell
3. INTEGRATIONPhage DNA integrates into
   bacterial DNA
4. REPLICATIONIntegrated Prophage replicates when
   bacterial DNA replicates
5. These cells may show new properties

Steps of the Lysogenic Cycle