Lesson 7: Viruses

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Lesson 7 Viruses
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What are viruses?

• Viruses small, non-living, infectious particles
  containing genetic material in the form of DNA or
  RNA with a protein capsule, called the capsid.
• Non-cellular particle

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• Over 4000 viruses species classified but
  scientists believe that there are millions
• Highly specific about what they invade (ex plant
  viruses infect only plant cells) specialize in
  the cell types they infect.

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Features of Viruses

• Viruses have no cytoplasm
• Less than 0.1µm in diameter (100s of thousands of
  viruses could fit inside a human cell)
• Cannot grow or reproduce on their own
• Do not produce energy do not create waste
• Take control of the cell that they infect

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Viruses Living or Non-Living?

• Considered non-living because
• Do not metabolize energy
• Do not perform cellular respiration
• Cannot grow
• Cannot reproduce on their own (act as parasites)

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Shapes of Viruses
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Viral Diseases

• Mild viral diseases such as the common cold or
  chicken pox, or more severe viral diseases such
  as AIDS or cholera, are all infectious. They can
  spread quickly and cause an epidemic (outbreak
  confined to a geographical region) or a pandemic
  (widespread, global epidemic).

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Bacteriophages

• Viruses infect single host species or a few
  closely related hosts. Ex human immunodeficiency
  virus (HIV) infects certain types of immune
  system cells.
• Viruses that infect bacteria are called
  bacteriophages.

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Vaccination

• Vaccinations are such preventions against
  viruses.
• Vaccines are mixtures that contain weakened forms
  or parts of dangerous virus.
• When vaccines are injected into an individuals
  body, they trigger a response by the immune
  system without causing an infection.
• This exposure creates a form of chemical memory
  that allows the immune system to reach quickly if
  the individual ever comes in contact with the
  real virus.

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Infectious Cycles

• Viruses must invade a living host cell to
  reproduce
• There are two ways to do this
• 1. Lytic Cycle
• 2. Lysogenic Cycle

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• Homework
• Why are viruses considered to be non-living?
• What characteristics do viruses share with all
  living things?
• Which viral diseases are quite common and
  associated with the winter season?
• Explain the relationship between a viruss
  dormant period in a cell and the appearance of
  cold sores.

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• Research
• The human influence virus, H1N1 (2009- swine
  flu), was declared a pandemic by the World Health
  Organization (WHO). What criteria does the WHO
  use to designate a disease outbreak as
  pandemic? How many deaths are thought to have
  resulted from this pandemic? How many countries
  have reported cases of H1N1? How did Canada
  respond to this outbreak?

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• Research
• Visit the WHO website and choose any other viral
  disease and research its cause, symptoms,
  prevention and treatment (if any).

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• WATCH http//www.khanacademy.org/video/viruses?to
  picbiology