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Biology - Chp 19 - Bacteria And Viruses - PowerPoint

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Biology - Chp 19 - Bacteria And Viruses - PowerPoint

  1. 1. Chapter 19 Bacteria and Viruses
  2. 2. 19-1 Bacteria• The invention of the microscope opened our eyes to the hidden, living world around us• Microscopic life covers nearly every square centimeter of Earth
  3. 3. Prokaryotes• The smallest and most common microorganisms• Unicellular organisms that lack a nucleusand membrane bound organelles• bacteria
  4. 4. Classifying Prokaryotes• Until recently, all prokaryotes were placed in a single kingdom - monera• More recently, biologists have begun to appreciate that prokaryotes can be divided into two very different groups: the eubacteriaand the archaebacteria
  5. 5. Eubacteria• Eubacteria include a wide range of organisms with different lifestyles• Eubacteria live almost everywhere
  6. 6. Archaebacteria• Lack the same carbohydrates of eubacteria and also have different membrane lipids• Also, the DNA sequences of key archaebacterial genes are more like those of eukaryotes than those of eubacteria• Many archaebacteria live in extremely harsh environments
  7. 7. Identifying Prokaryotes• Prokaryotes are identified by characteristics such as shape, the chemical nature of their cell walls, the way they move and the way they obtain energy
  8. 8. Shapes• Bacilli – rod shaped• Cocci – spherical shaped• Spirilla – spiral and corkscrew shaped
  9. 9. Cell Walls• Eubacteria – have peptigoglycan• Archaebacteia – don’t have peptigoglycan
  10. 10. Movement• Some bacteria move differently than others
  11. 11. Metabolic Diversity• No characteristic of prokaryotes illustrates their diversity better than the way they obtain energy
  12. 12. Heterotrophs• Must take inorganic molecules for both energy and a supply of carbon
  13. 13. Photoheterotrophs• These organisms are photosynthetic using sunlight for energy but they also need to take in organic compounds as a carbon source
  14. 14. Photoautotrophs• Use light energy to convert carbon dioxide and water to carbon compounds and oxygen in a process similar to that used by green plantsEx.) cyanobacteria (blue-green algae)
  15. 15. Chemoautotrophs• Can perform chemosynthesis• Make organic carbon molecules from carbon dioxide• Unlike photoautotrophs, however they do not require light as a source of energy. Instead they use energy directly from chemical reactions
  16. 16. Releasing Energy• Like all organisms, bacteria need a constant supply of energy• This energy is released by the process of cellular respiration or fermentation or both
  17. 17. Obligate aerobes• Require a constant supply of oxygen in order to live
  18. 18. Obligate anaerobes• Do not require oxygen and if fact may be killed by it
  19. 19. Facultative anaerobes• Can survive with or without oxygen
  20. 20. Growth and Reproduction• Bacteria can grow really fast• If unlimited space and food were available to a single bacterium and if all of its offspring divided every 20 minutes in just 48 hours they would reach a mass of approximately 4000 times the mass of the earth!
  21. 21. Binary Fission• When a bacterium has grown so that it has nearly doubled in size, it replicates its DNA and divides in half producing 2 identical daughter cells
  22. 22. Binary Fission• Bacterial reproduction, asexual reproduction
  23. 23. Conjugation• Many bacteria are also able to exchange genetic information by a process called conjugation• This transfer of genetic information increases genetic diversity
  24. 24. Spore Formation• When growth conditions become unfavorable, many bacteria form structures called spores
  25. 25. Endospore• A type of spore formed when a bacterium produces a thick internal wall that encloses a thick internal wall that encloses its DNA and a portion of its cytoplasm
  26. 26. Endospore
  27. 27. Importance of Bacteria• Bacteria are vital to maintaining the living world• Some are producers that capture energy by photosynthesis• Others are decomposers that break down the nutrients in dead matter and the atmosphere• Still other bacteria have human uses
  28. 28. Decomposers• As decomposers, bacteria help the ecosystem recycle nutrients, therefore maintaining equilibrium in the environment
  29. 29. Nitrogen Fixers• You may recall that plants need nitrogen to make amino acids, the building blocks of protiens• Nitrogen gas (N2) makes up approximately 80 percent of Earth’s atmosphere• However, plants can’t use nitrogen gas directly• Nitrogen must first be changed chemically to ammonia (NH3) or other nitrogen compounds
  30. 30. Nitrogen fixation• Process which turns unusable nitrogen gas into useful nitrogen containing compounds• Allows nitrogen atoms to continually cycle through the biosphere• Many plants have symbiotic relationships with nitrogen fixing bacteria
  31. 31. Human Uses of Bacteria• Used in food and beverage production• Industries: petroleum, water, mining, drugs• Inside of us (symbiosis) – E.coli• Drug research
  32. 32. 19 – 2 Viruses
  33. 33. Viruses• Particles of nucleic acid, protein, and sometimes lipids• Viruses can reproduce only by infecting living cells• A typical virus is composed of a core of DNA or RNA surrounded by a protein coat• Viruses are very small. They can only be seen with an electron microscope
  34. 34. Capsid• A viruses protein coat• The capsid proteins of a typical virus bind to receptors on the surface of a cell and “trick” the cell into allowing it inside• Once inside, the viral genes are expressed and causes the host cell to make copies of the virus and in the process the host cell is destroyed• Because viruses must bind precisely to proteins on the cell surface and then use a hosts genetic system, most viruses are highly specific to the cells they infect
  35. 35. Viral Infection• Once the virus is inside the host cell, two different processes may occur
  36. 36. Lytic Infection• In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst
  37. 37. A literary approach to lytic virus infectionsIn its own way, a lytic virus is similar to adesperado in the Old West. First, the outlaweliminates the town’s existing authority (host cellDNA). Then, the desperado demands to beoutfitted with new weapons, horses, and ridingequipment by terrorizing the local people (usingthe host cell to make proteins). Finally, thedesperado forms a gang that leaves the town toattack new communities (the host cell bursts,releasing hundreds of virus particles).
  38. 38. Lysogenic Infection• In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cells DNA• Unlike lytic viruses, lysogenic viruses do not lyse the host cell right away. Instead, a lysogenic virus remains inactive for a period of time• Eventually, only one of a number of factors may activate the DNA of a prophage which will then remove itself from the host cell DNA and direct the synthesis of new viruses particles
  39. 39. Retroviruses• Viruses that contain RNA as their genetic information• When retroviruses infect a cell, they produce a DNA copy of their RNA• Ex.) HIV
  40. 40. Viruses and Living Cells• Viruses must infect a living cell in order to grow and reproduce• They also take advantage of the host’s respiration, nutrition and all the other functions that occur in living things• Therefore, viruses are considered to be parasites
  41. 41. Parasites• organisms that live on or in a host organism from which it obtains nutrients, and it usually does harm to the host
  42. 42. Are viruses alive? Cells and VirusesCharacteristic Cell VirusStructure Cell membrane, cytoplasm; eukaryotes also contain nucleus and organellesReproduction Independent cell division either asexually or sexuallyGenetic Code DNAGrowth and Development Yes; in multicellular organisms, cells increase in number and differentiateObtain and Use Energy yesResponse to Environment yesChange Over Time yes
  43. 43. 19 – 3 Diseases Caused by Bacteria and Viruses• Bacteria and viruses are everywhere in nature, but only a few cause disease
  44. 44. Pathogens• Disease causing agents• All viruses reproduce by infecting living cells, and disease results when the infection causes harm to the host• All bacteria require nutrients and energy: however, disease results when bacteria interfere with the host’s ability to obtain enough of those elements to function properly
  45. 45. Bacterial Disease in Humans • Bacteria produce disease in one of two general ways 1. Some bacteria damage the cells and tissues of the host by breaking down the cells for food 2. Other bacteria release toxins that travel throughout the body interfering with the normal activity of the host
  46. 46. Preventing Bacterial Disease • Many bacterial disease can be prevented by stimulating the bodies immune system with vaccines
  47. 47. Vaccine• A preparation of weakened or killed pathogen• When injected into the body, a vaccine sometimes prompts the body to produce immunity to the disease• If a bacterial infection does occur, a number of drugs can be used to attack and destroy the invading bacteria
  48. 48. Antibiotics• Compounds that block the growth and reproduction of bacteria
  49. 49. Controlling Bacteria• There are various methods used to control bacterial growth, including sterilization, disinfectants, and food processing
  50. 50. Sterilization by Heat• Many bacteria cannot survive high temperatures for a long time, so most can be killed by exposure to high heat• Ex.) pasteurization
  51. 51. Disinfectants• Chemical solutions that kill pathogenic bacteria
  52. 52. Food Storage and Processing• Food that is stored at a low temperature will stay fresh longer because bacteria cannot reproduce fast at cold temperatures• Also, a lot of the processing procedures that are used in the food industry raise the temperature of food to a point where the bacteria are killed
  53. 53. Viral Disease in Humans• Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium• Unlike bacterial diseases, viruses can’t be treated with antibiotics• The best way to protect against most viral diseases lies in prevention by the use of vaccines
  54. 54. Viral Disease in Animals• Viruses produce serious animal disease as well• Ex.) Foot-and-mouth disease, Rous sarcoma
  55. 55. Viral Disease in Plants• Many viruses infect plants• Ex.) Tobacco mosaic virus, potato yellow dwarf virus
  56. 56. Viroids and Prions• Scientists have discovered two virus-like particles that also cause disease
  57. 57. Viroids• Single stranded RNA molecules that have no surrounding capsid• Cause disease in plants
  58. 58. Prions• Proteins that cause disease in animalsEx.) Mad cow disease

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