Viruses

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Viruses Diseases Objective 3
The student will demonstrate an understanding of
the interdependence of organisms and the
environment.
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Interdependence
Viruses and organisms relyon their
environmentand other species for survival.
3
Viruses

• Viruses are NOT cells. A virus is an infectious
  agent made up of
• a core of nucleic acid (RNA or DNA)
• a capsid (protein coat)

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Alive or not?
Even scientists disagree as to whether or not
viruses are alive. What do you think? Look at the
chart on the next page to help you decide.
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Characteristic of life
CELL VIRUS
Made of cells YES NO
Obtain use energy YES NO
Grow develop YES Only inside a living cell
Reproduce YES Only inside a living cell
Respond adapt YES YES
Contain RNA or DNA YES YES
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Structureof a virus
ENVELOPE

• Envelope (part of the protein coat)
• Capsid (part of the protein coat)
• Nucleic acid (either DNA or RNA)

NUCLEIC ACID
CAPSID
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Retrovirus
CAPSID

• A virus that contains RNA instead of DNA
• Human Immunodeficiency Virus (HIV) is a
  retrovirus
• HIV causes AIDS
• The HIV virus destroys the bodys helper T cells

ENVELOPE
RNA
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Bacteriophage

• A virus that only infects bacteria

CAPSID
HEAD
DNA
CAPSID
TAIL FIBER
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Ticking time bombs . . .
Viruses do not reproduce. They invade a living
cell and let the cell do the work for them.
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Lytic Cycle
The viral infection that rapidly kills the host
cell is the lytic cycle.
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Cycle Illustration
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2
3
4
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Lysogenic Cycle
The viral infection that enters a cell, remains
harmless for a period of time (sometimes years),
and then becomes harmful later is called the
lysogenic cycle.
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Role of viruses

• All viruses act like parasites, harming the host
  cell.
• Viruses cause disease in every kind of
  organismanimals, plants, fungi, protists, and
  bacteria.

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Some viral diseases

• HIV
• Measles
• Smallpox
• Influenza
• Chicken pox

• Common cold
• Herpes
• Warts
• Mononucleosis
• Mumps

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Viral diseases

• usually cannot be cured, but many can be
  prevented by
• Good hygiene (i.e. washing hands etc.)
• Immunization (vaccines)
• Vaccines are weakened viruses that cause your
  body to produce antibodies to help fight off the
  pathogen

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Links
http//www.virology.net/Big_Virology/BVFamilyIndex
.html
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Sources

http//www.virology.net/Big_Virology/BVFamilyIndex
.html Biology, Kenneth R. Miller Joseph
Levine, 1991, Prentice-Hall, Inc., Englewood
Cliffs NJ. Biology The Web of Life, Eric
Strauss Marylin Lisowski, 1998, Scott Foresman
Addison Wesley, Menlo Park CA TAKS Power Tools,
Glencoe Science, Glencoe McGraw-Hill, 2001, New
York, NY. Microsoft Office Clipart