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Viruses - PowerPoint PPT Presentation

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Viruses. STRUCTURE. Nonliving Composed of a nucleic acid and a protein coat Cause many diseases Virology – Study of Viruses Comparison of Viruses and Cells below. Structure of a Virus. Nucleic acid (DNA or RNA).

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  • Nonliving
  • Composed of a nucleic acid and a protein coat
  • Cause many diseases
  • Virology – Study of Viruses
  • Comparison of Viruses and Cells below

Structure of a Virus

Nucleic acid (DNA or RNA)

Protein Coat ( capsid)

characteristics of viruses
Characteristics of Viruses

2 essential features

  • 1. Nucleic Acid
    • May be DNA or RNA
    • Helical, closed loop, or long strand
  • 2. Protein Coat – called CAPSID
  • Some have ENVELOPE
    • Ex. Influenza, chickepox, herpes simplex, HIV
    • Icosahedron – 20 triangular faces
      • Ex.) herpes, chickenpox, polio
    • Helix – Coiled spring
      • EX.)Rabies, measles, tobacco mosaic
grouping viruses
Grouping Viruses
  • Grouped according to:
    • Presence of capsid and envelope – shape
    • RNA or DNA, single or double stranded – structure
other grouping of viruses
Other Grouping of Viruses
  • Viroids- The smallest known particle that can replicate.
    • Disrupt plant cell metabolism
    • Can destroy entire crops
  • Prions – Abnormal forms of proteins that clump together inside cells.
    • Clumping eventually kills the cell
    • Examples
      • Scrapie – in sheep
      • Mad Cow Disease
viral replication
Viral Replication
  • Can replicate only by invading host cell and using its enzyme and organelles.
  • Bacteriophage – viruses that infect bacteria
    • Used to study viruses
lytic cycle of virus replication
Lytic Cycle of Virus Replication
  • Lytic Cycle
    • Viral genome is released into the host cell
    • Replication follows immediately
    • Cellular components used to make new viruses
    • Viral enzyme kills cell.
    • Play animation
lysogenic cycle of virus replication
Lysogenic Cycle of Virus Replication
  • Nucleic acid of virus becomes part of the host cell’s chromosome
  • Nucleic acid remains in the cell in this form for many generations
  • HIV follows this pattern
  • HIV infects WBC and remains as proviruses
  • As immune system fails, opportunistic infections occur = AIDS
  • Play animation
  • Play animation
viruses and human disease
Viruses and Human Disease
  • Control and Prevention of spread.
    • Vaccination & Antiviral drugs
      • Ex.) chickenpox vaccine, AZT, Acyclovir, protease inhibitors.
  • Emerging Viruses – exist in isolated habitats
    • Do not usually infect humans unless environmental conditions favor contact.
  • Several viruses are now linked to cancers such as leukemia, liver cancer, Burkitt’s lymphoma, cervical cancer.

After polio infections, the killer T-cell have destroyed the motor neurons that are producing the virus. The result is a loss of muscle control including the diaphragm. The iron lung changes the pressure to pump air in and out of the lungs.

Look at how the virus infects