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