Viruses

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Viruses
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Is a Virus a Living Organism?

• Chapter 1 Properties of life
• Cellular Respiration
• Reproduction
• Metabolism
• Homeostasis
• Heredity
• Responsiveness
• Growth and development

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Viruses are not living organisms

• Viruses do not
• Grow
• Have homeostasis
• Metabolize
• Viruses do
• Infect cells and use the cell to make more
  viruses
• Cause disease in many organisms

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Parts of a Virion (a virus particle)

• Nucleic Acid RNA or DNA
• Capsid protein coat that surrounds the DNA or
  RNA in a virus
• Lipid Membrane a membrane around the capsid in
  many kinds of viruses helps the virus enter
  cells (enveloped viruses without the membrane,
  the virus is naked)
• Made of proteins, lipids, and glycoproteins

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RNA or DNA?

• Viruses with RNA
• Human immunodeficiency virus (HIV)
• Influenza viruses
• Rabies
• Viruses with DNA
• Warts
• Chickenpox
• mononucleosis

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Virus Shapes

• Helical
• Rodlike with capsid proteins winding around the
  core in a spiral
• Tobacco Mosaic Virus

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Virus Shapes

• Polyhedral
• Has many sides
• Most polyhedral capsids have 20 sides and 12
  corners

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Virus Shapes

• Polyhedral capsid attached to a helical tail.

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How do viruses replicate?

• 2 methods of replication
• 1. Lytic Cycle the virus enters the cell,
  replicates itself hundreds of times, and then
  bursts out of the cell, destroying it.
• 2. Lysogenic Cycle the virus DNA integrates
  with the host DNA and the hosts cell helps
  create more virus DNA. An environmental change
  may cause the virus to enter the Lytic Cycle.

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• In the lytic cycle, the virus reproduces itself
  using the host cell's chemical machinery. The red
  spiral lines in the drawing indicate the virus's
  genetic material. The orange portion is the outer
  shell that protects it.

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• In the lysogenic cycle, the virus reproduces by
  first injecting its genetic material, indicated
  by the red line, into the host cell's genetic
  instructions.

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Viruses Enter Living Cells

• Viruses enter bacterial cells by punching a hole
  in the cells wall and injecting its DNA

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Viruses Enter Living Cells

• Viruses enter plant cells through tiny rips in
  the cell wall.
• Viruses enter animal cells by endocytosis.

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Mutating viruses

• Viruses can mutate when they copy the genetic
  material
• Copy something wrong
• Mistake proves useful
• More powerful virus (more infectious)
• Viruses dont mutate often, except
• Influenza
• HIV

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Viruses are host cell specific.

• Most viruses are restricted to certain kinds of
  cells (those that infect plants cannot infect
  animal cells).
• Why?
• Scientists think that viruses originated from
  escaped genetic material from host cells.

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Viruses can be beneficial

• Bacteriophages attack destroy bacteria
• Baculovirus ebola-like virus that attacks
  insects
• Could use for pest control in crops
• Cabbage loopers eat
• cabbage crops
• Virus can kill pests in days
• (its really gross)
• and then there are those that are not so good.

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The spread of West Nile virus (1999 2002)
bird, horse, mosquito or human
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Also important

• Any agent (not just viruses) that causes disease
  is a pathogen.
• When a virus inserts its genetic material into a
  hosts DNA, it is called a provirus.
• Some viruses replicate very slowly and only cause
  damage when the conditions are right. (cold
  sores)

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Human Immunodeficiency Virus (HIV)Acquired
Immuno Deficiency Syndrome (AIDS)
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Basic Structure

• Viral envelope lipid bilayer glycoproteins
  protrude from surface
• Glycoproteins enable virus to recognize surface
  proteins of special immune cells and to enter the
  cell (like a key to the cells door)
• 2 strands RNA only 9 genes 3 are found in many
  viruses (structural proteins)
• Reverse Transcriptase turns RNA into DNA (this
  makes HIV a retrovirus) DNA instructs cell to
  make more viruses

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HIV Making Factories

• Virus enters cell through endocytosis
• Virus replicates RNA to DNA with reverse
  transcriptase

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• DNA enters nucleus binds with host DNA
• New virions exit cell through exocytosis to
  infect other cells (notice cell isnt destroyed)

• mRNA is created (carries instructions for making
  new viral proteins) and leaves nucleus
• Uses host cells enzymes to make new viruses

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How Is HIV Spread?

• Sexual contact
• Sharing contaminated needles
• Blood transfusions
• Breast feeding (mother to baby)
• Mother to baby during pregnancy or birth

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Think about it

• In the US, there is better than a 1/1000 chance
  of contracting HIV during unprotected sex
• A person can be contagious for more than 10 years
  before any sign of the disease is apparent
• HIV becomes AIDS when the number of immune cells
  drops below a predetermined number
• No one dies from HIV or AIDS people die from
  secondary infections (ranging from the common
  cold to cancer)
• More than 3 million people (size of Chicago) die
  each year
• There are approx. 14,000 new cases of HIV
  worldwide every day

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