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16 Lecture Ppt

  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 16 Evolution of Microbial Life
  2. 2. Viruses Reproduce in Living Cells 16-
  3. 3. 16.1 Viruses have a simple structure <ul><li>The size of a virus is comparable to that of a large protein macromolecule, ranging from 0.2 to 2 μm </li></ul><ul><li>All viruses possess the same basic anatomy </li></ul><ul><ul><li>An outer capsid , which is composed of protein </li></ul></ul><ul><ul><li>An inner core of nucleic acid (DNA or RNA) </li></ul></ul><ul><ul><ul><li>A viral genome has as few as three and as many as 100 genes </li></ul></ul></ul><ul><li>The covering of a virus contains the capsid, which may be surrounded by an outer membranous envelope </li></ul><ul><ul><li>If not, the virus is said to be naked. Naked viruses can be transmitted by contact with inanimate objects, such as desktops </li></ul></ul>16-
  4. 4. 16-
  5. 5. Figure 16.1A Adenovirus, a naked virus, with a polyhedral capsid and a fiber at each corner 16-
  6. 6. Figure 16.1B Influenza virus, surrounded by an envelope with spikes 16-
  7. 7. 16.2 Some viruses reproduce inside bacteria <ul><li>All sorts of cells, whether prokaryotic or eukaryotic, are susceptible to a viral infection </li></ul><ul><li>Viruses are specific </li></ul><ul><ul><li>Specificity extends to the type of cell infected by the virus </li></ul></ul><ul><ul><ul><li>Example: tobacco mosaic virus infects only tobacco leaves </li></ul></ul></ul><ul><li>Bacteriophages , or simply phages, are viruses that parasitize bacteria </li></ul><ul><ul><li>Two types of bacteriophage life cycles </li></ul></ul><ul><ul><ul><li>Lytic cycle and the Lysogenic cycle </li></ul></ul></ul>16-
  8. 8. Figure 16.2 The lytic and lysogenic cycles in prokaryotes 16-
  9. 9. APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES 16.3 Viruses are responsible for a number of plant diseases <ul><li>Approximately 2,000 kinds of plant diseases have been attributed to viruses </li></ul><ul><ul><li>Plant viruses are responsible for the loss of over 15 billion dollars annually by reducing the yield of important agricultural and horticultural crops </li></ul></ul><ul><li>Once a plant is infected the virus spreads slowly throughout the plant </li></ul><ul><li>In some instances, plants have been purposefully infected with a virus in order to produce traits considered desirable by gardeners </li></ul><ul><ul><ul><li>Example: Some variegation in leaves and flowers can be brought about by viruses </li></ul></ul></ul>16-
  10. 10. Figure 16.3A The tobacco mosaic virus (TMV) is responsible for discoloration in the leaves of tobacco plants 16-
  11. 11. Figure 16.3B A virus is responsible for the variegation and streaking in Rembrandt tulips 16-
  12. 12. 16.4 Viruses reproduce inside animal cells and cause diseases <ul><li>Replication of an animal virus with a DNA genome involves certain steps </li></ul><ul><ul><li>Attachment: Glycoprotein spikes projecting through the envelope allow the virus to bind to host cells </li></ul></ul><ul><ul><li>Penetration: After the viral particle enters the host cell, uncoating follows and viral DNA enters the host </li></ul></ul><ul><ul><li>Biosynthesis: The capsid and other proteins are synthesized by host cell ribosomes according to viral DNA instructions </li></ul></ul><ul><ul><li>Maturation: Viral proteins and DNA replicates are assembled to form new viral particles </li></ul></ul><ul><ul><li>Release: In an enveloped virus, budding occurs and the virus develops its envelope </li></ul></ul>16-
  13. 13. Figure 16.4 Replication of an animal virus 16-
  14. 14. 16.5 The AIDS virus exemplifies RNA retroviruses <ul><li>Genome for an HIV virus consists of RNA, instead of DNA </li></ul><ul><li>HIV is a retrovirus. It uses reverse transcription from RNA into DNA in order to insert a complementary copy of its genome into the host’s genome </li></ul>16-
  15. 15. Figure 16.5 Reproduction of HIV 16-
  16. 16. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 16.6 Humans suffer from emerging viral diseases <ul><li>Emergent diseases - newly recognized as infectious </li></ul><ul><ul><li>International travel facilitates disease transmission </li></ul></ul><ul><li>Viruses are constantly in a state of evolutionary flux </li></ul><ul><ul><li>A new pathogen can emerge through the acquisition of new surface antigens </li></ul></ul><ul><li>Some viruses can easily move from animals to humans </li></ul><ul><ul><li>Example: Rabies can be spread by the bite of a rabid animal, such as a skunk, raccoon, bat, cat or dog </li></ul></ul><ul><li>Many viruses are transmitted by vectors, usually insects that carry pathogens from an infected individual or reservoir to a healthy individual </li></ul><ul><ul><li>Mosquitoes serve as a common vector for several viral diseases, including West Nile virus and yellow fever </li></ul></ul>16-
  17. 17. Figure 16.6A Surgical masks provide protection against the transmission of SARS 16-
  18. 18. Figure 16.6B Exterminating possibly infected chickens may protect against bird flu 16-
  19. 19. The First Cells Originated on Early Earth 16-
  20. 20. 16.7 Experiments show how small organic molecules may have first formed <ul><li>Two different hypotheses to explain how organic molecules could have formed </li></ul><ul><ul><li>Prebiotic Soup Hypothesis </li></ul></ul><ul><ul><ul><li>The early atmosphere contained no oxygen and was a reducing environment </li></ul></ul></ul><ul><ul><ul><li>In such an environment, methane, ammonia, hydrogen, and water could be reduced to a variety of amino acids and organic acids </li></ul></ul></ul><ul><ul><li>Iron-Sulfur World Hypothesis </li></ul></ul><ul><ul><ul><li>At hydrothermal vents on the ocean floor, cool water is heated to a temperature as high as 350°C, and when it spews back out, it contains various mixed iron and nickel sulfides that can change N 2 to NH 3 </li></ul></ul></ul>16-
  21. 21. Figure 16.7A Laboratory re-creation of chemical evolution in the atmosphere 16-
  22. 22. Figure 16.7B Chemical evolution at hydrothermal vents 16-
  23. 23. 16.8 RNA may have been the first macromolecule <ul><li>Two stages in origin of life </li></ul><ul><ul><li>Chemical Evolution </li></ul></ul><ul><ul><ul><li>Organic monomers arise from inorganic compounds and polymers arise when monomers join together </li></ul></ul></ul><ul><ul><li>Biological Evolution </li></ul></ul><ul><ul><ul><li>A plasma membrane surrounds polymers producing a protocell </li></ul></ul></ul><ul><ul><ul><li>A true cell has arisen when the cell reproduces in the same manner as today’s cells </li></ul></ul></ul><ul><li>RNA-First Hypothesis </li></ul><ul><ul><li>The first macromolecules need to have enzymatic functions, not only to allow the genetic material to replicate, but also to perform any number of metabolic functions </li></ul></ul><ul><ul><li>This has led research to conclude it was an “RNA world” some 4 BYA and that RNA chains were the first forms of life </li></ul></ul>16-
  24. 24. Figure 16.8 The origin of the first cell(s) can be broken down into these steps 16-
  25. 25. 16.9 Protocells preceded the first true cells <ul><li>Origin of Plasma Membrane - First and foremost, the protocell would have had an outer membrane </li></ul><ul><ul><li>Two hypotheses on origin of first plasma membrane </li></ul></ul><ul><ul><ul><li>If lipids are made available to microspheres, which are protein, they acquire a lipidprotein outer membrane </li></ul></ul></ul><ul><ul><ul><li>Liposomes - Lipids naturally organize themselves into double-layered bubbles, roughly the size of a cell </li></ul></ul></ul>16-
  26. 26. Figure 16.9A Microspheres, which are made of protein, could have acquired an outer lipid-protein membrane during the origin of the first cell 16-
  27. 27. Figure 16.9B Liposomes, which are composed of lipids, have a double-layered outer membrane 16-
  28. 28. Origin of DNA Information System <ul><li>A protocell became a cell when it contained a DNA information system </li></ul><ul><ul><li>DNA to RNA to Proteins </li></ul></ul><ul><li>To make DNA, a ribozyme could have acted in the same manner as the enzyme reverse transcriptase </li></ul><ul><ul><li>RNA is unique in that it could have also synthesized the proteins that took over most of the enzymatic functions in cells </li></ul></ul>16-
  29. 29. Origin of Metabolism to Acquire Energy <ul><li>The cell would have had to carry on nutrition so that it could grow </li></ul><ul><li>Two theories </li></ul><ul><ul><li>If organic molecules formed in the atmosphere </li></ul></ul><ul><ul><ul><li>Nutrition would have been no problem because simple organic molecules could have served as food </li></ul></ul></ul><ul><ul><ul><li>Thus the protocell was a heterotroph </li></ul></ul></ul><ul><ul><li>If the protocell evolved at hydrothermal vents </li></ul></ul><ul><ul><ul><li>It may have carried out chemosynthesis </li></ul></ul></ul><ul><ul><ul><li>Synthesizing organic molecules by oxidizing inorganic compounds, such as hydrogen sulfide (H 2 S) </li></ul></ul></ul>16-
  30. 30. Both Bacteria and Archaea Are Prokaryotes 16-
  31. 31. 16.10 Prokaryotes have particular structural features <ul><li>Prokaryotes are unicellular organisms </li></ul><ul><ul><li>Range in size from 1-10 μm in length and 0.7-1.5 μm in width </li></ul></ul><ul><li>Prokaryote means “before a nucleus” </li></ul><ul><ul><li>These organisms lack a eukaryotic nucleus, but have a dense area called a nucleoid, consisting of a circular strand of DNA </li></ul></ul><ul><li>Three Basic Shapes of Prokaryotes </li></ul><ul><ul><li>Cocci (sing., coccus) - round or spherical </li></ul></ul><ul><ul><li>Bacilli (sing., bacillus) - rod-shaped </li></ul></ul><ul><ul><li>Spirilla (sing., spirillum) - spiral- or helical-shaped </li></ul></ul>16-
  32. 32. Figure 16.10A Anatomy of bacteria 16-
  33. 33. Figure 16.10B The three shapes of prokaryotes 16-
  34. 34. 16.11 Prokaryotes have a common reproductive strategy <ul><li>Figure 16.11A Binary fission results in two bacteria </li></ul>16-
  35. 35. Formation of Endospores in Bacteria <ul><li>When faced with unfavorable environmental conditions, some bacteria form endospores </li></ul><ul><ul><li>A portion of the cytoplasm and a copy of the chromosome dehydrate and are then encased by a heavy, protective spore coat </li></ul></ul>16-
  36. 36. Figure 16.11B Endospores within Clostridium tetani , a bacterium 16-
  37. 37. 16.12 How genes are transferred in bacteria <ul><li>Transformation - a recipient bacterium picks up from its surroundings free pieces of DNA secreted by live prokaryotes or released by dead prokaryotes </li></ul><ul><li>Conjugation - the donor bacterium passes DNA to the recipient by way of a sex pilus, which temporarily joins the two bacteria </li></ul><ul><li>Transduction - bacteriophages carry portions of bacterial DNA from a donor cell to a recipient </li></ul><ul><ul><li>When a bacteriophage injects its DNA into the donor cell, the phage DNA takes over the machinery of the cell and causes it to produce more phage particles </li></ul></ul>16-
  38. 38. Figure 16.12A Gene transfer by transformation 16-
  39. 39. <ul><li>Figure 16.12B Gene transfer by conjugation </li></ul>16-
  40. 40. Figure 16.12C Gene transfer by transduction 16-
  41. 41. 16.13 Prokaryotes have various means of nutrition <ul><li>Obligate Anaerobes - unable to grow in the presence of free oxygen </li></ul><ul><ul><li>A few serious illnesses—such as botulism, gas gangrene, and tetanus—are caused by anaerobic bacteria </li></ul></ul><ul><li>Facultative anaerobes - able to grow in either presence or absence of oxygen </li></ul><ul><li>Most prokaryotes are aerobic and require a constant supply of oxygen </li></ul>16-
  42. 42. Autotrophic Prokaryotes <ul><li>Some prokaryotes produce their own organic nutrients </li></ul><ul><li>Photoautotrophs use solar energy to reduce carbon dioxide to organic compounds </li></ul><ul><ul><li>Two types of photoautotrophic bacteria </li></ul></ul><ul><ul><ul><li>Those that evolved first and do not give off oxygen </li></ul></ul></ul><ul><ul><ul><li>Those that evolved later and do give off oxygen </li></ul></ul></ul><ul><li>Chemoautotrophs remove electrons from inorganic compounds, such as hydrogen gas, hydrogen sulfide, and ammonia, and to reduce CO 2 to an organic molecule </li></ul>16-
  43. 43. Figure 16.13A Some anaerobic photosynthetic bacteria live in the muddy bottom of eutrophic lakes 16-
  44. 44. Figure 16.13B Some chemosynthetic prokaryotes live at hydrothermal vents 16-
  45. 45. Chemoheterotrophic Prokaryotes <ul><li>Many prokaryotes are aerobic saprotrophs </li></ul><ul><ul><li>They secrete digestive enzymes into the environment to breakdown large organic molecules to smaller ones to be absorbed </li></ul></ul><ul><li>In ecosystems, saprotrophic bacteria are called decomposers </li></ul><ul><ul><li>They play a critical role in recycling matter and make inorganic molecules available to photosynthesizers </li></ul></ul>16-
  46. 46. 16.14 The cyanobacteria are ecologically important organisms <ul><li>Perform photosynthesis like plants and are likely the first to have generated oxygen </li></ul><ul><li>Some possess heterocysts for nitrogen fixation </li></ul><ul><li>Common in aquatic habitats and some harsh habitats </li></ul><ul><li>Some are symbiotic with other organisms (e.g. lichens are cyanobacteria and fungi) </li></ul>16-
  47. 47. 16.15 Some archaea live in extreme environments <ul><li>Archaea are found in extreme environments </li></ul><ul><ul><li>hot springs, thermal vents, and salt basins </li></ul></ul><ul><li>They may have diverged from a common ancestor relatively soon after life began </li></ul><ul><li>Structure and Function </li></ul><ul><ul><li>Plasma membranes of archaea contain unusual lipids that allow them to function at high temperatures </li></ul></ul><ul><ul><li>Some have unique forms of metabolism </li></ul></ul><ul><ul><ul><li>Methanogens have the unique ability to form methane </li></ul></ul></ul>16-
  48. 48. Types of Archaea <ul><li>Figure 16.15A Methanogen habitat and structure </li></ul>16-
  49. 49. Figure 16.15B Halophile habitat and structure 16-
  50. 50. Figure 16.15C Thermoacidophile habitat and structure 16-
  51. 51. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 16.16 Prokaryotes have environmental and medical importance <ul><li>Prokaryotes are everywhere </li></ul><ul><ul><li>Prokaryotes are most cosmopolitan of all life-forms and are virtually everywhere </li></ul></ul><ul><ul><ul><li>Found in oceans, our intestines, hot springs, and soil </li></ul></ul></ul><ul><li>Prokaryotes were and are environmentally important </li></ul><ul><ul><li>Ancient photosynthetic cyanobacteria released copious amounts of oxygen </li></ul></ul><ul><ul><li>Prokaryotes play an essential role in the carbon nitrogen, sulfur, and phosphorus environmental cycles </li></ul></ul>16-
  52. 52. Prokaryotes Are Medically Important 16-
  53. 53. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 16.17 Disease-causing microbes can be biological weapons <ul><li>Biological warfare is the use of viruses and bacteria as weapons of war </li></ul><ul><li>Likely agents to be used by bioterrorists </li></ul><ul><ul><li>Anthrax - from the bacterium Bacillus anthracis </li></ul></ul><ul><ul><li>Smallpox - caused by the variola virus </li></ul></ul><ul><ul><li>Botulism - caused by the toxin of the anaerobic bacterium Clostridium botulinum </li></ul></ul><ul><ul><li>Plague - from the bacterium Yersinia pestis , has been called the Black Death and bubonic plague </li></ul></ul><ul><ul><li>Tularemia - caused by the bacterium Francisella tularensis </li></ul></ul><ul><ul><li>Hemorrhagic fevers - caused by several types of viruses, are characterized by high fever and severe bleeding from several organs </li></ul></ul>16-
  54. 54. Connecting the Concepts: Chapter 16 <ul><li>Viruses are noncellular, disease-causing agents </li></ul><ul><ul><li>Medical significance of viruses cannot be underestimated </li></ul></ul><ul><ul><li>Humans use viruses for gene research and even for gene therapy </li></ul></ul><ul><li>Prokaryotes are cellular, but their structure is simpler than eukaryotes </li></ul><ul><ul><li>They lack a nucleus and membranous organelles </li></ul></ul><ul><li>Many prokaryotes live in environments that may resemble habitats available when Earth first formed </li></ul><ul><ul><li>We find prokaryotes in such hostile habitats as swamps, the Dead Sea, and hot sulfur springs </li></ul></ul><ul><ul><li>Cyanobacteria are believed to have introduced oxygen into the Earth’s ancestral atmosphere </li></ul></ul><ul><ul><li>Most bacteria are decomposers that recycle nutrients in both aquatic and terrestrial environments </li></ul></ul>16-