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Chapter 17

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Chapter 17

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  1. Chapter 17 Viruses & prokaryotes

  2. 17-1 Viruses • What is a virus? • How do viral life cycles differ? • What is the relationship between viruses and their hosts?

  3. What is a virus? • A virus is a noncellular particle made up of genetic material and protein that can invade living cells • First discovered in 1935 by an American scientist named Wendell Stanley • It was called the tobacco mosaic virus or TMV

  4. TMV on tobacco plant


  6. Structure of a virus • Composed of a core of DNA or RNA surrounded by a protein coat called a capsid • Capsid protects the genetic material • The core contains several genes to several hundred genes


  8. More complex structures are in viruses called bacteriophages – viruses that invade bacteria • Has a head region (capsid), a nucleic acid core, and a tail • Some have tail fibers that allow them to attach to the bacteria


  10. Viruses are rod-shaped, tadpole-shaped, helical and cubelike shaped • Vary in size from 20 to 400 nanometers • A nanometer is one billionth of a meter


  12. Specificity of a virus • Specific viruses infect specific organisms • Plant virus cannot infect an animal • Only mammal viruses that do not infect other animals and vise versa • Viruses for every type of organism


  14. Life cycle of a Lytic Virus • In order to reproduce, viruses must invade, or infect, a living host cell • They also invade in different ways… • One way is done by lytic viruses where when they invade the cell bursts or lyses

  15. Life cycle of a lytic virus

  16. Infection • A virus is activated by contact with the right host cell (chance) • It then injects its DNA into the cell

  17. Life cycle of a lytic virus

  18. Growth • The RNA polymerase of the host cell creates messenger RNA of the virus DNA • This mRNA then takes over the host cell • Some proteins turn off the creation of molecules for the cell

  19. Life cycle of a lytic virus

  20. Replication • It then uses the host cell to make thousands of copies of its own protein coat and DNA • The host cell is then filled with viral DNA molecules • These three steps can happen in 25 minutes

  21. Life cycle of a lytic virus

  22. The infected cell then lyses (bursts) and releases hundreds of virus particles • These particles than infect other cells • The host cell is lysed and destroyed so this process is called lytic infection


  24. Lysogenic Infection • Lysogenic infection-the virus does not reproduce and lyse its host cell • The DNA of the virus enters the cell and is inserted into the DNA of the host cell • The viral DNA is then known as a prophage

  25. Prophage activity • Blocks entry of other viruses and may even add useful DNA to the host cell’s DNA • Eventually it will remove itself from the DNA and create new virus particles


  27. Retroviruses • Retroviruses contain RNA as their genetic information • When they enter the cell they produce a DNA copy • This then enters into the host cells DNA


  29. Viruses and Living Cells • Viruses must infect living cells to carry out their functions • Viruses are parasites-an organism that depends entirely upon another living organism for its existence in such a way that it harms that organism


  31. Are viruses alive? • Viruses are not made of cells • They can grow, reproduce, regulate gene expression, an evolve • It is up for debate

  32. Virus video

  33. 17-2 Prokaryotic Cells Bacteria Intro video

  34. Prokaryotes • Cells that do not have a nucleus

  35. Eubacteria

  36. Cyanobacteria

  37. Archaeabacteria • Methanogens – archaeabacteria that produces methane gas

  38. Prochlorobacteria

  39. Bacteria (E. Coli) • One-celled prokaryotes

  40. They do not contain the complex range of membrane enclosed organelles that are found in most eukaryotic cells

  41. Eubacteria Structure • generally surrounded by a cell wall made of carbohydrates • there is a cell membrane which surrounds the cytoplasm • long whip like flagella protrude from the membrane through the cell wall

  42. Eubacteria

  43. They use photosynthesis to get energy

  44. Fresh and saltwater, land, hot water, arctic, grow on snow

  45. Methanogens are archaebactria that produce methane gas

  46. prochlorobacteriamore related to chloroplasts[1].jpg

  47. Bacteria Identification • cell shape • Cell Wall • Bacterial Movement • How the obtain energy

  48. Bacterial shape

  49. Gram Staining • There are two types of dye, The bacterial cells with only one thick layer of carbohydrate and protein molecules outside the cell membrane took up the crystal violet. The bacterial cells that have lipid and carbohydrate molecules appear red under the microscope and are gram negative

  50. Gram Staining