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Viruses

Viruses. Characteristics of Viruses. A small, nonliving particle that invades and then reproduces inside a living cell. Nonliving because… Viruses are not cells. Do not use energy to grow or to respond to their surroundings. Cannot make food, take in food, or produce wastes.

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Viruses

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  1. Viruses

  2. Characteristics of Viruses • A small, nonliving particle that invades and then reproduces inside a living cell. • Nonliving because… • Viruses are not cells. • Do not use energy to grow or to respond to their surroundings. • Cannot make food, take in food, or produce wastes. • Act as a parasite • Obtain energy from host and may cause harm to their host.

  3. Naming Viruses • Don’t use binomial nomenclature (nonliving) • Variety of names. • Ex. Tobacco mosaic virus, Ebola, Epstein-Barr

  4. Shape & Size of Viruses • Viruses vary widely in shape. • Vary greatly in size. • Much smaller than bacteria.

  5. Structure of Viruses • 2 Components • Outer Coat • Made of proteins • Protects the virus • Helps the virus attach to the surface of the host cell • Inner Core of Genetic Material • Either DNA or RNA

  6. How Viruses Multiply • Basic Mechanism • Attachment • Virus enters cell • Virus’s genetic material takes over the cell’s functions • Genetic material directs the cell to produce the virus’s proteins and genetic material • Proteins and genetic materials are then assembled into new viruses • KEY DIFFERENCE: Some viruses take over the cell’s function immediately while others wait for awhile.

  7. Lytic vs. Lysogenic Viruses • Lytic “Active” Virus • Virus immediately takes over cell’s functions and new viruses are rapidly produced • Eventually the cell bursts.

  8. Lysogenic Cycle • Instead of going into action to make more viruses, the virus’s DNA becomes part of the cell’s genetic material. • Does not affect cell’s function for awhile. • After a period of time, the cell will suddenly enter the lytic cycle.

  9. Viral Diseases

  10. Preventing Infectious Diseases • Vaccine • A substance that stimulates the body to produce chemicals that destroy viruses or bacteria. • May be made from dead or altered viruses or bacteria. • Does not cause the disease but activates the body’s natural defenses and effectively puts the body “on alert” for possible virus or bacteria invasion.

  11. Summary Questions • Explain why viruses are considered nonliving. • Describe the basic structure of a virus. • Describe how viruses multiply. • You have a case of the flu. A friend recommends a new treatment advertised in a magazine. The ad states that the treatment works by “deactivating the virus’s nucleus so it can’t reproduce.” Could this treatment cure you? Explain.

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