1. CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 24 Early Life and the Diversification of Prokaryotes

2. © 2014 Pearson Education, Inc.  Earth formed 4.6 billion years ago  The oldest fossil organisms are prokaryotes dating back to 3.5 billion years ago  Prokaryotes are single-celled organisms in the domains Bacteria and Archaea  Some of the earliest prokaryotic cells lived in dense mats that resembled stepping stones Overview: The First Cells

3. © 2014 Pearson Education, Inc. Figure 24.1

4. © 2014 Pearson Education, Inc.  Prokaryotes are the most abundant organisms on Earth  There are more in a handful of fertile soil than the number of people who have ever lived  Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms  Some prokaryotes colonize the bodies of other organisms

5. © 2014 Pearson Education, Inc. Figure 24.2

6. © 2014 Pearson Education, Inc. Concept 24.1: Conditions on early Earth made the origin of life possible  Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages 1.Abiotic synthesis of small organic molecules 2.Joining of these small molecules into macromolecules 3.Packaging of molecules into protocells, membrane- bound droplets that maintain a consistent internal chemistry 4.Origin of self-replicating molecules

7. © 2014 Pearson Education, Inc. Synthesis of Organic Compounds on Early Earth  Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, and hydrogen)  As Earth cooled, water vapor condensed into oceans, and most of the hydrogen escaped into space

8. © 2014 Pearson Education, Inc.  In the 1920s, A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment  In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible

9. © 2014 Pearson Education, Inc.  However, the evidence is not yet convincing that the early atmosphere was in fact reducing  Instead of forming in the atmosphere, the first organic compounds may have been synthesized near volcanoes or deep-sea vents  Miller-Urey-type experiments demonstrate that organic molecules could have formed with various possible atmospheres  Organic molecules have also been found in meteorites Video: Hydrothermal VentVideo: Tubeworms

10. © 2014 Pearson Education, Inc. Figure 24.3a

11. © 2014 Pearson Education, Inc. Abiotic Synthesis of Macromolecules  RNA monomers have been produced spontaneously from simple molecules  Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

12. © 2014 Pearson Education, Inc. Protocells  Replication and metabolism are key properties of life and may have appeared together  Protocells may have been fluid-filled vesicles with a membrane-like structure  In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer

13. © 2014 Pearson Education, Inc.  Adding clay can increase the rate of vesicle formation  Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment

14. © 2014 Pearson Education, Inc. Figure 24.4 Vesicle boundary Precursor molecules only 1  m Relative turbidity, an index of vesicle number (a) Self-assembly Time (minutes) 0.4 0.2 0 0 20 40 60 Precursor molecules plus montmorillonite clay 20  m (c) Absorption of RNA(b) Reproduction

15. © 2014 Pearson Education, Inc. Self-Replicating RNA  The first genetic material was probably RNA, not DNA  RNA molecules called ribozymes have been found to catalyze many different reactions  For example, ribozymes can make complementary copies of short stretches of RNA

16. © 2014 Pearson Education, Inc.  Natural selection has produced self-replicating RNA molecules  RNA molecules that were more stable or replicated more quickly would have left the most descendant RNA molecules  The early genetic material might have formed an “RNA world”

17. © 2014 Pearson Education, Inc.  Vesicles with RNA capable of replication would have been protocells  RNA could have provided the template for DNA, a more stable genetic material

18. © 2014 Pearson Education, Inc. Fossil Evidence of Early Life  Many of the oldest fossils are stromatolites, layered rocks that formed from the activities of prokaryotes up to 3.5 billion years ago  Ancient fossils of individual prokaryotic cells have also been discovered  For example, fossilized prokaryotic cells have been found in 3.4-billion-year-old rocks from Australia

19. © 2014 Pearson Education, Inc. Figure 24.5 Time (billions of years ago) 10  m 30  m 5 cm Nonphotosynthetic bacteria Cyanobacteria Stromatolites Possible earliest appearance in fossil record 432 1 0

20. © 2014 Pearson Education, Inc.  The cyanobacteria that form stromatolites were the main photosynthetic organisms for over a billion years  Early cyanobacteria began the release of oxygen into Earth’s atmosphere  Surviving prokaryote lineages either avoided or adapted to the newly aerobic environment

21. © 2014 Pearson Education, Inc. Concept 24.2: Diverse structural and metabolic adaptations have evolved in prokaryotes  Most prokaryotes are unicellular, although some species form colonies  Most prokaryotic cells have diameters of 0.5–5 µm, much smaller than the 10–100 µm diameter of many eukaryotic cells  Prokaryotic cells have a variety of shapes  The three most common shapes are spheres (cocci), rods (bacilli), and spirals

22. © 2014 Pearson Education, Inc. Figure 24.6 3  m (a) Spherical (b) Rod-shaped (c) Spiral 1  m

23. © 2014 Pearson Education, Inc. Cell-Surface Structures  A key feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment  Eukaryote cell walls are made of cellulose or chitin  Bacterial cell walls contain peptidoglycan, a network of modified sugars cross-linked by polypeptides

24. © 2014 Pearson Education, Inc.  Archaeal cell walls contain polysaccharides and proteins but lack peptidoglycan  Scientists use the Gram stain to classify bacteria by cell wall composition  Gram-positive bacteria have simpler walls with a large amount of peptidoglycan  Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic

25. © 2014 Pearson Education, Inc. Figure 24.7 Peptido- glycan layer Cell wall Gram-negative bacteria 10  m Gram-positive bacteria (b) Gram-negative bacteria (a) Gram-positive bacteria Plasma membrane Plasma membrane Peptidoglycan layer Cell wall Outer membrane Carbohydrate portion of lipopolysaccharide

26. © 2014 Pearson Education, Inc.  Many antibiotics target peptidoglycan and damage bacterial cell walls  Gram-negative bacteria are more likely to be antibiotic resistant  A polysaccharide or protein layer called a capsule covers many prokaryotes

27. © 2014 Pearson Education, Inc. Figure 24.8 Bacterial cell wall Bacterial capsule Tonsil cell 200 nm

28. © 2014 Pearson Education, Inc.  Some bacteria develop resistant cells called endospores when they lack an essential nutrient  Other bacteria have fimbriae, which allow them to stick to their substrate or other individuals in a colony  Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA

29. © 2014 Pearson Education, Inc. Figure 24.9 Fimbriae 1  m

30. © 2014 Pearson Education, Inc. Motility  In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from a stimulus  Chemotaxis is the movement toward or away from a chemical stimulus

31. © 2014 Pearson Education, Inc.  Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends  Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently

32. © 2014 Pearson Education, Inc. Figure 24.10 Flagellum Filament 20 nm Hook Motor Cell wall Rod Peptidoglycan layer Plasma membrane

33. © 2014 Pearson Education, Inc. Internal Organization and DNA  Prokaryotic cells usually lack complex compartmentalization  Some prokaryotes do have specialized membranes that perform metabolic functions  These are usually infoldings of the plasma membrane

34. © 2014 Pearson Education, Inc. Figure 24.11 Respiratory membrane 0.2  m 1  m Thylakoid membranes (a) Aerobic prokaryote(b) Photosynthetic prokaryote

35. © 2014 Pearson Education, Inc.  The prokaryotic genome has less DNA than the eukaryotic genome  Most of the genome consists of a circular chromosome  The chromosome is not surrounded by a membrane; it is located in the nucleoid region  Some species of bacteria also have smaller rings of DNA called plasmids

36. © 2014 Pearson Education, Inc. Figure 24.12 Plasmids 1  m Chromosome

37. © 2014 Pearson Education, Inc. Nutritional and Metabolic Adaptations  Prokaryotes can be categorized by how they obtain energy and carbon  Phototrophs obtain energy from light  Chemotrophs obtain energy from chemicals  Autotrophs require CO 2 as a carbon source  Heterotrophs require an organic nutrient to make organic compounds

38. © 2014 Pearson Education, Inc.  Energy and carbon sources are combined to give four major modes of nutrition  Photoautotrophy  Chemoautotrophy  Photoheterotrophy  Chemoheterotrophy

39. © 2014 Pearson Education, Inc. Table 24.1

40. © 2014 Pearson Education, Inc. The Role of Oxygen in Metabolism  Prokaryotic metabolism varies with respect to O 2  Obligate aerobes require O 2 for cellular respiration  Obligate anaerobes are poisoned by O 2 and use fermentation or anaerobic respiration, in which substances other than O 2 act as electron acceptors  Facultative anaerobes can survive with or without O 2

41. © 2014 Pearson Education, Inc. Nitrogen Metabolism  Nitrogen is essential for the production of amino acids and nucleic acids  Prokaryotes can metabolize nitrogen in a variety of ways  In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N 2 ) to ammonia (NH 3 )

42. © 2014 Pearson Education, Inc. Reproduction  Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours  Key features of prokaryotic biology allow them to divide quickly  They are small  They reproduce by binary fission  They have short generation times

43. © 2014 Pearson Education, Inc. Adaptations of Prokaryotes: A Summary  The ongoing success of prokaryotes is an extraordinary example of physiological and metabolic diversification  Prokaryotic diversification can be viewed as a first great wave of adaptive radiation in the evolutionary history of life

44. © 2014 Pearson Education, Inc.  Prokaryotes have considerable genetic variation  Three factors contribute to this genetic diversity  Rapid reproduction  Mutation  Genetic recombination Concept 24.3: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes

45. © 2014 Pearson Education, Inc. Genetic Recombination  Genetic recombination, the combining of DNA from two sources, contributes to diversity  Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation  Movement of genes among individuals from different species is called horizontal gene transfer

46. © 2014 Pearson Education, Inc. Transformation and Transduction  A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation  Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)

47. © 2014 Pearson Education, Inc. Figure 24.15-1 1 Phage infects bacterial donor cell with A  and B  alleles. Donor cell A  B  Phage DNA

48. © 2014 Pearson Education, Inc. Figure 24.15-2 2 1 Phage infects bacterial donor cell with A  and B  alleles. Phage DNA is replicated and proteins synthesized. Donor cell AA BB A  B  Phage DNA

49. © 2014 Pearson Education, Inc. Figure 24.15-3 32 1 Phage infects bacterial donor cell with A  and B  alleles. Phage DNA is replicated and proteins synthesized. Fragment of DNA with A  allele is packaged within a phage capsid. Donor cell AA AA BB A  B  Phage DNA

50. © 2014 Pearson Education, Inc. 432 1 Phage infects bacterial donor cell with A  and B  alleles. Phage DNA is replicated and proteins synthesized. Fragment of DNA with A  allele is packaged within a phage capsid. Phage with A  allele infects bacterial recipient cell. Recipient cell Crossing over Donor cell A − B − AA AA AA BB A  B  Phage DNA Figure 24.15-4

51. © 2014 Pearson Education, Inc. Figure 24.15-5 Phage infects bacterial donor cell with A  and B  alleles. Incorporation of phage DNA creates recombinant cell with genotype A  B . Phage DNA is replicated and proteins synthesized. Fragment of DNA with A  allele is packaged within a phage capsid. Phage with A  allele infects bacterial recipient cell. Recombinant cell Recipient cell Crossing over Donor cell A  B − A − B − AA AA AA BB A  B  Phage DNA 5 432 1

52. © 2014 Pearson Education, Inc. Conjugation and Plasmids  Conjugation is the process where genetic material is transferred between prokaryotic cells  In bacteria, the DNA transfer is one way  In E. coli, the donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA

53. © 2014 Pearson Education, Inc. Figure 24.16 Sex pilus 1  m

54. © 2014 Pearson Education, Inc.  The F factor is a piece of DNA required for the production of pili  Cells containing the F plasmid (F + ) function as DNA donors during conjugation  Cells without the F factor (F – ) function as DNA recipients during conjugation  The F factor is transferable during conjugation

55. © 2014 Pearson Education, Inc. Figure 24.17-1 1 One strand of F  cell plasmid DNA breaks at arrowhead. Bacterial chromosome Bacterial chromosome F plasmid Mating bridge F  cell (donor) F − cell (recipient)

56. © 2014 Pearson Education, Inc. Figure 24.17-2 2 1 One strand of F  cell plasmid DNA breaks at arrowhead. Bacterial chromosome Bacterial chromosome F plasmid Mating bridge F  cell (donor) F − cell (recipient) Broken strand peels off and enters F − cell.

57. © 2014 Pearson Education, Inc. Figure 24.17-3 32 1 One strand of F  cell plasmid DNA breaks at arrowhead. Bacterial chromosome Bacterial chromosome F plasmid Mating bridge F  cell (donor) F − cell (recipient) Broken strand peels off and enters F − cell. Donor and recipient cells synthesize complementary DNA strands.

58. © 2014 Pearson Education, Inc. Figure 24.17-4 432 1 One strand of F  cell plasmid DNA breaks at arrowhead. Bacterial chromosome Bacterial chromosome F plasmid Mating bridge F  cell (donor) F − cell (recipient) F  cell F  cell Broken strand peels off and enters F − cell. Recipient cell is now a recombinant F  cell. Donor and recipient cells synthesize complementary DNA strands.

59. © 2014 Pearson Education, Inc.  The F factor can also be integrated into the chromosome  A cell with the F factor built into its chromosomes functions as a donor during conjugation  The recipient becomes a recombinant bacterium, with DNA from two different cells

60. © 2014 Pearson Education, Inc. R Plasmids and Antibiotic Resistance  Genes for antibiotic resistance are carried in R plasmids  Antibiotics kill sensitive bacteria, but not bacteria with specific R plasmids  Through natural selection, the fraction of bacteria with genes for resistance increases in a population exposed to antibiotics  Antibiotic-resistant strains of bacteria are becoming more common

61. © 2014 Pearson Education, Inc. Bacteria  Bacteria include the vast majority of prokaryotes familiar to most people  Diverse nutritional types are scattered among the major groups of bacteria Video: Tubeworms

62. © 2014 Pearson Education, Inc. Figure 24.UN01 Eukarya Bacteria Archaea

63. © 2014 Pearson Education, Inc.  Cyanobacteria are photoautotrophs that generate O 2  Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis

64. © 2014 Pearson Education, Inc.  Gram-positive bacteria include  Actinomycetes, which decompose soil  Streptomyces, which are a source of antibiotics  Bacillus anthracis, the cause of anthrax  Clostridium botulinum, the cause of botulism  Some Staphylococcus and Streptococcus, which can be pathogenic  Mycoplasms, the smallest known cells

65. © 2014 Pearson Education, Inc. Figure 24.19bd Gram-positive bacteria Streptomyces, the source of many antibiotics (SEM) 5  m

66. © 2014 Pearson Education, Inc. Figure 24.19be Gram-positive bacteria Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) 2  m

67. © 2014 Pearson Education, Inc. Archaea  Archaea share certain traits with bacteria and other traits with eukaryotes

68. © 2014 Pearson Education, Inc. Table 24.2a

69. © 2014 Pearson Education, Inc. Table 24.2b

70. © 2014 Pearson Education, Inc.  Some archaea live in extreme environments and are called extremophiles  Extreme halophiles live in highly saline environments  Extreme thermophiles thrive in very hot environments Video: Cyanobacteria (Oscillatoria)

71. © 2014 Pearson Education, Inc. Figure 24.20

72. © 2014 Pearson Education, Inc.  Methanogens produce methane as a waste product  Methanogens are strict anaerobes and are poisoned by O 2  Methanogens live in swamps and marshes, in the guts of cattle, and near deep-sea hydrothermal vents

73. © 2014 Pearson Education, Inc. Chemical Recycling  Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems  Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms and waste products

74. © 2014 Pearson Education, Inc. Ecological Interactions  Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont  Prokaryotes often form symbiotic relationships with larger organisms

75. © 2014 Pearson Education, Inc.  In mutualism, both symbiotic organisms benefit  In commensalism, one organism benefits while neither harming nor helping the other in any significant way  In parasitism, an organism called a parasite harms but does not kill its host  Parasites that cause disease are called pathogens

76. © 2014 Pearson Education, Inc. Impact on Humans  The best-known prokaryotes are pathogens, but many others have positive interactions with humans

77. © 2014 Pearson Education, Inc. Mutualistic Bacteria  Human intestines are home to about 500–1,000 species of bacteria  Many of these are mutualists and break down food that is undigested by our intestines

78. © 2014 Pearson Education, Inc. Pathogenic Bacteria  Prokaryotes cause about half of all human diseases  For example, Lyme disease is caused by a bacterium and carried by ticks

79. © 2014 Pearson Education, Inc. Figure 24.24 5  m

80. © 2014 Pearson Education, Inc.  Bacteria can now be used to make natural plastics  Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment  Bacteria can be engineered to produce vitamins, antibiotics, and hormones  Bacteria are also being engineered to produce ethanol from waste biomass

81. © 2014 Pearson Education, Inc. Figure 24.UN04 Fimbriae Cell wall Capsule Flagella Sex pilus Internal organization Circular chromosome