The Biology of Viruses

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The Biology of Viruses
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Where do viruses fit in the 3 domain, 6 kingdom
classification of life?

• Viruses do not fit into the classification of
  life because they are not considered to be living
  things
• Not composed of cells
• Cannot reproduce on their own

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Properties of Viruses

• 1. Extremely Small
• 2. Simple
• A) nucleic acid core surrounded by
• B) outer protective protein coat called a capsid

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The Structure of Viruses
Tobacco Mosaic Virus
HIV
Bacteriophage
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Properties of Viruses

• 1. Extremely Small
• 2. Simple
• A) nucleic acid core surrounded by
• B) outer protective protein coat called a capsid
• 3. Contain DNA or RNA
• 4. Genetic material may be single or
  double-stranded

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Viral Reproduction

• Viruses have a very simple function invade a
  host cell and start reproducing
• Each virus infects only a limited number of host
  cells, this is called its host range
• Viruses identify their hosts by a lock and key
  fit between proteins on the outside of the virus
  and receptor molecules on the surface of the host
• A virus which infects and destroys bacterial
  cells is a bacteriophage

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Viral Replication

• Read and summarize the 4 steps of viral
  replication on page 336
• What is a virulent phage?
• What is a temperate phage? How does replication
  in a temperate phage differ from replication in a
  virulent phage?

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Viral Replication

• What is a virulent phage?
• A virus which causes lysis (death) of the cell it
  invades
• What is a temperate phage? How does replication
  in a temperate phage differ from replication in a
  virulent phage?
• A virus whose DNA becomes integrated into its
  host cell and passed on to the hosts daughter
  cells
• These viruses do not destroy the cells they
  infect unless they enter the lytic cycle

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Lytic vs Lysogenic Cycles
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Viral Infections

• Common cold, influenza, herpes, HIV
• Prevention
• Vaccines containing inactivated viruses will
  artificially trigger an immune response
• Body produces antibodies against the virus
• Treatment
• Antiviral medications are designed to interfere
  with viral replication or strengthen the bodys
  immune response against the virus