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9/13/11 The Importance of Prokaryotes KEY POINTS 1. Decomposers: recycle organic and inorganic molecules in environment; makes them available to other organisms. 2. Essential components of symbioses. 3. Encompasses the origins of metabolism and metabolic diversity. 4. Origin of photosynthesis and formation of atmospheric Oxygen PROKARYOTES Domains Bacteria & Archaea ANTIQUITY ic zo oMes zoic Cenozoic General characteristics Humans leo Pa Colonization of land Animals Bil lio 2 ns of Archaean m Proterozoic Small No organelles Cell wall Numerous -5µ 4 1 1. 2. 3. 4. 0.5 Origin of solar system and Earth Prokaryotes go sa ar 3 ye Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen 1 9/13/11 General characteristics General characteristics 6. Important decomposers and recyclers 7. Symbionts a. Parasites b. Commensalists c. Mutualists 5. Metabolic diversity established nutritional modes of eukaryotes. TAXONOMY is problematic • Relationships obscured by billions of years of evolution • Also obscured by unique bacterial means of recombination (more later). • Grouped primarily by DNA sequence data. • Immense genetic/genomic diversity. i. Endosymbiotic theory for origin of Eukaryotes ii. Cellulose consumption by animals iii. Essential nutrients iv. Other cool examples Current taxonomy is stabilizing • Note that Prokaryote is paraphyletic. Why? • Two Domains: • Archaea: extremophiles (mostly), ancient, probable progenitors of eukaryotes. • Bacteria: most commonly-encountered prokaryotes. 2 9/13/11 Cell Surface • • Archaea: plasma membrane of ether-lipids (unique in life). Bacteria: a sugar polymer peptidoglycan Motility • ~half the species can move. 1. Flagella 2. Spiral filaments: spirochetes corkscrew 3. Gliding • Capable of taxis Cell Surface • Fimbriae & pili Genome • Small genomes: ~1/1000th DNA content of eukaryotes. • No nucleus. • ‘nucleoid region. • Circular chromosome • Plasmids 3 9/13/11 Genome: Recombination via transformation • DNA taken up from the environment Genome: Recombination via transduction • Transfer of DNA via phage viruses. Genome: Recombination via conjugation • Direct transfer of DNA between cells. • Both plasmids and portions of bacterial chromosome. Reproduction & Growth • Meiosis & Mitosis NOT PRESENT. • Asexual binary fission. 4 9/13/11 Metabolism Metabolic Diversity: Metabolism Source of Carbon Metabolic Diversity • Nutrition: • Requires a source of carbon • Requires a source of energy • AUTOTROPHS: Need only carbon dioxide (CO2) as carbon source • HETEROTROPHS: Need at least one organic nutrient as carbon source (e.g. glucose; petroleum) • Both of these present in domain Eucarya as well. Metabolic Diversity: Metabolism Source of Energy Metabolism Metabolic Diversity: Combined • PHOTOTROPHS: Need only sunlight as energy source • CHEMOTROPHS: Derive energy from oxidation of organic molecules. Carbon Source: • Both of these present in domain Eucarya as well. Energy Source: Sun Environment CO2 Photoautotroph Chemoautotroph Organic molecules Photoheterotroph Chemoheterotroph Which of these are present in multicellular Eucarya? 5 9/13/11 Metabolism Photoautotrophs Chemoautotrophs • Oxidize inorganics (H2S, NH3) for energy. • Need only CO2 as carbon source. • Unique to Bacteria and Archaea. • E.g. Methanococcus jannaschii lives on hydrothermal vents at 2600m below sea level. • Reduces H2 + CO2 to CH4 + 2H2O. • Use sun for energy, CO2 for carbon. • Photosynthetic bacteria (e.g. cyanobacteria). • Present in many plants and singlecelled Eucarya Metabolism Photoheterotrophs • Get enery from light but must obtain carbon in organic form (NOT CO2). • Unique to Bacteria and Archaea. • E.g. Halobacterium salinarium. Metabolism Chemoheterotrophs Metabolism • Consume organic molecules for both energy and carbon. • Common among prokaryotes: – saprobes (decomposers) – parasites (rely on living hosts) • Also widespread in Protista, Animalia, Plantae. 6 9/13/11 Metabolism Nitrogen metabolism • Nitrogen fixation: • N2 to ammonia (NH3) to ammonium (NH4+). • Essential for multicellular life! Taxonomy of Prokaryotes • Archaea or Archaebacteria – Methanogens – Halophiles – Thermophiles • Bacteria or Eubacteria – – – – – Protobacteria Chlamyidias Spirochetes Cyanobacteria Gram-positive bacteria Oxygen Relationships • Aerobic vs. Anaerobic • Obligate aerobes • Cellular respiration: • Facultative anaerobes • Fermentation: • Obligate anaerobes • Anaerobic respiration: Archaea or Archaebacteria • Live in extreme environments (extremophiles): sulfur hot springs, deep sea vents, high salt environments. • Lack peptidoglycan, unique plasma membrane of liquids • Likely sister group of Eukaryotes 7 9/13/11 Prokaryotes: Summary • You should now have a good sense of prokaryote biology and diversity. • Including roles in metabolism, symbioses, global energy cycles. • Important distinguishing characteristics of cell wall, motility, genome, replication. • General aspects of their systematics. 8