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Viruses

Viruses. 10B Part I . Intro. Viruses are strange particles that are not classified as living but made of biological or organic compounds They have to have a living host to multiply Their main purpose – cause disease and often death . Discovery of Viruses.

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Viruses

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  1. Viruses 10B Part I

  2. Intro • Viruses are strange particles that are not classified as living but made of biological or organic compounds • They have to have a living host to multiply • Their main purpose – cause disease and often death

  3. Discovery of Viruses • 1890s – DimitriIwanowski filtered particles that were causing tobacco mosaic disease and thought a toxin produced from a bacterium • Later in the 1930s, Wendell Stanley was able to isolate and purify those particles that were multiplying inside the cells of tobacco leaves Virus – comes from a Latin word meaning poison…

  4. A Virus… Many scientists were stumped. • Virus particles do not multiply when isolated and alone • But somehow the virus grows and reproduces when placed on living tissue… • Is the virus alive? Or a non-living chemical? • Do the cells make more virus? • Does the virus alter the genes of the leaf cells? • Does the virus supply genes to the cell to make more virus?

  5. Structure of Viruses • Viruses are made of 2 main parts: • Core – DNA or RNA (never both) • Capsid – outer covering made of tough protein; could also be surrounded by an envelope

  6. Structure cont…

  7. Virus Shapes • Virus shapes are determined by their DNA/RNA • Shapes include: • Helix – spiral shape (Tobacco mosaic virus) • Icosahedron – 20 triangular sides • Spherical – (HIV) • Cylindrical and spiral - Ebola

  8. Classification • Viruses are classified based on: • What type of nucleic acid they contain; either DNA or RNA • Shape • Presence or absence of an envelope • Method of infecting and replicating inside a host cell

  9. Viroids and Prions • Even smaller than viruses are other agents that cause disease!  viroids and prions • A viroidis simply a short circular strand of RNA without a capsid or envelope that can still replicate inside a host cell • Can cause Hepatitus D and plant diseases • A prion is smaller than even a viroid and is an abnormally shaped protein that can cause disease • Can cause BSE (bovine spongiform encephalitis) • Or aka – mad cow disease

  10. Smallpox • “The most dangerous epidemic is the smallpox...which sweeps at times like a storm of death over the land.” • Richard Burton, 1860 • Dr. Edward Jenner, an English doctor and scientist in the late 1700s noticed that milkmaids and dairy workers seemed to be immune to the deadly smallpox disease • He developed a way to expose an individual to small amounts of cowpox (similar to smallpox) that would make that person immune to the actual disease

  11. Vaccines • This process called vaccination(“of cows”) is not a cure for a disease but rather a way of developing an immunity by exposing someone to a weaker or similar form of a disease • 200 years after Dr. Jenner developed the vaccination process, the World Health Organization has almost eliminated the global threat of smallpox.

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