TEK for this lesson

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TEK for this lesson

• The student is expected to
• Compare the structures and functions of viruses
  to cells and describe the role of viruses in
  causing diseases and conditions such as acquired
  immune deficiency syndrome, common colds, small
  pox, influenza, and warts.

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What is virology?
the study of viruses
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• 6 Kingdoms

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Description
Viruses occur in all organisms and can only
reproduce in living cells.
They are not living organisms because..
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They do not have the capability to grow and
replicate on their own.
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Viruses are Small! 5 billion viruses can fit into
a drop of blood Can only be seen with electron
microscope
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Discovery
Wendell Stanley extracts Tobacco Mosaic Virus
(TMV) in 1933.
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TMV is a rod shaped RNA molecule surrounded by a
coat protein.
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Definition

• Segment of DNA or RNA surrounded by a protein
  coat or capsid
• Some animal viruses
• contain an envelope surrounding the capsid
• contain glycoproteins that to bind to the surface
  of the host cell

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Viruses Shapes
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Viral Infection

• Virus injects its own DNA or RNA into the cell
  and takes control
• Makes hundred of copies of itself
• Breaks out and destroys the cell

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Some animal viruses are equipped with an outer
membrane, or viral envelope outside the capsid.
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• HIV virus
• infects and eliminates key cells of the immune
  system
• destroys the bodys ability to defend itself from
  cancer or infections.

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HIV Reproductive Cycle
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HIV Treatment

• Combination drug therapy
• Protease inhibitors and AZT

2. Defective HIV gene (nef) as potential vaccine
3. Chemokines block cell membrane receptors
4. Disabling receptors in cell membranes
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Emerging Viruses
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Influenza virus Bird or killer flu killed 21
million in 1918 100 thousand in 1957 17 thousand
in 1968
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Prions from sheep brain are responsible for
mad-cow disease!
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Prions are proteinaceous infectious particles
that result in damaged brain tissue.
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• Bacteriophages
• viruses that infect bacteria.
• punch a hole in the cell wall and inject DNA into
  the cell

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Some kill the host, while others are integrated
into the host genome.
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The lytic cycle of Bacteriophage T4 ends in the
death of the host cell.
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The lysogenic cycle replicates the virus without
destroying the host.