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19-2 Viruses

19-2 Viruses. By: Katelyn, Rose and Ashley . What is a Virus?. Viruses- particles of nucleic acid, protein and sometimes lipids Most viruses are so small, they can only be seen through a powerful electron microscope.

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19-2 Viruses

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  1. 19-2 Viruses By: Katelyn, Rose and Ashley

  2. What is a Virus? • Viruses- particles of nucleic acid, protein and sometimes lipids • Most viruses are so small, they can only be seen through a powerful electron microscope. • A typical virus is composed of a core of DNA or RNA surrounded by a protein coat. • The more complex the virus is the more genes it contains • They enter a living cell and once inside, use machinery of infected cell to produce more viruses

  3. Living characteristics of viruses: • They reproduce at a good rate, but only in living host cells. • They can mutate.

  4. Nonliving characteristics of viruses Nonliving characteristics of viruses • They are acellular, that is, they contain no cytoplasm or cellular organelles. • viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell. • They possess DNA or RNA but never both.

  5. Virus Structures

  6. What is a Capsid? • Capsid- a protein coat • The capsid enable’s host cells to enter the virus • The capsid proteins “trick” the virus by binding the surface of the cell allowing the capsid to come inside the cell • The cell transcribes and translates the viral genetic information into viral capsid proteins. • Sometimes it causes the host cell to make copies of the virus, and it causes the host cell to be destroyed

  7. Bacteriophages- viruses that infect bacteria • Once the virus is inside the host cell two different process may occur • In a lytic infection, a virus enters a cell and replicates itself and causes the cell to burst. • In the lysogenic infection the virus replicates itself in a way that doesn’t kill the host cell immediately.

  8. Lytic and Lysogenic Infections

  9. Prophage and Viral Infections Prophage - viral DNA that is embedded in the host cell’s DNA Prophage may remain part of the DNA for many generations before being active A virus may not always stay in the prophage Eventually one factor will activate the DNA of a prophage causing it to remove itself form the host cell DNA and direct the synthesis of a new virus particles

  10. What are Retroviruses? • Retroviruses- viruses that contain RNA as their genetic information • When retroviruses infect a cell they produce a DNA copy of their RNA • The DNA is then inserted into the DNA of the host cell

  11. Viruses and Living Cells • In order for a virus to grow it must infect a living cell • Viruses are parasites • After infecting living cells viruses can reproduce • Viruses are borderline of living and none living things • Viruses are smaller and simpler than cells

  12. Review : • What are the two ways the two ways viruses cause infections?

  13. Answer: 1.Lysogenic and lytic

  14. Review: 2. What are typical viruses composed of?

  15. Answer: • Core of DNA or RNA surrounded by protein coat

  16. Review: • What is the viruses protein coat called?

  17. Answer: • capsid

  18. Review: • How do viruses “reproduce”?

  19. Answer: • They enter a living cell and once inside, use machinery of infected cell to produce more viruses

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