VIRUSES

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VIRUSES

• Magnet Biology

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Characteristics of Viruses

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

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Structure of Viruses

• All viruses consist of 2 basic parts
• nucleic acid (genetic material)
• protein coat (capsid)
• Capsid protein coat containing inner core of DNA
  or RNA
• May have tail fibers and projections to aid in
  attachment
• Some have extra outer layer called envelope

Animation http//www.johnkyrk.com/virus.html
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Structure of Viruses

• Several types of viral arrangements classified by
  the type of nucleic acid
• Adenovirus (common cold)
• Influenza virus (flu)
• Bacteriophage (infects bacteria)
• Tobacco mosaic virus

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Viral recognition and 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
• 1. Lytic cycle
• 2. Lysogenic cycle

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Lytic Cycle

• Lytic cycle viral DNA takes over host nucleus,
  produces new viruses, the cell fills with new
  viruses, at the end the cell bursts and the cell
  dies

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Steps of the Lytic Cycle

1. ATTACHMENT virus attaches to the cell surface

2. ENTRYinjects DNA, takes over host nucleus
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3. REPLICATIONreproduces virus parts 4.
ASSEMBLYputs virus parts together into mature
viruses
5. RELEASE/LYSEScell splits open releasing
viruses that can infect others
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Lytic Cycle

• Active infections immediate symptoms appear 1-4
  days after exposure to the virus (common cold and
  flu)
• http//www.rattlerscience.com/life/classes/apbiolo
  gy/documents/Unit2010/18_Lectures_PPT/media/18_06
  PhageT4LyticCycle_A.swf

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Lysogenic Cycle

• Viral genetic material enters into the chromosome
  of a host cell
• Viral genetic material is mixed with host DNA

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Lysogenic Cycle

• Does not immediately begin to reproduce, host may
  function normally while virus stays dormant
• Provirus can pop out at any time and begin
  reproducing
• Example Herpes (cold sores, fever blisters) The
  infected cell will have the viral genes
  permanently
• Reactivation results in the lytic cycle
• http//www.rattlerscience.com/life/classes/apbiolo
  gy/documents/Unit2010/18_Lectures_PPT/media/18_07
  LysogenicLyticCycles_A.swf

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