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Prokaryotes

Prokaryotes. The Origins of Metabolic Diversity. Lightning Strike. The World of Prokaryotes. Prokaryotes were the earliest organisms They are not only the most numerous organisms, but also the most pervasive Prokaryotes are microscopic and perform vital functions

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Prokaryotes

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  1. Prokaryotes The Origins of Metabolic Diversity Lightning Strike

  2. The World of Prokaryotes • Prokaryotes were the earliest organisms • They are not only the most numerous organisms, but also the most pervasive • Prokaryotes are microscopic and perform vital functions • Prokaryotes often live in symbiotic relationships – endosymbiosis p. 502 - 503 Tornado on the road

  3. p. 503 Point of reference

  4. An Explosion of Diversity • Modern prokaryotes are diverse in structure and physiology • About 5000 species are known • Estimated range: 400,000 – 4 million • “A true sense of biodiversity requires a “downward adjustment of scale” p. 503 Hydrogen Explosion

  5. Bacteria and Archaea • The two main branches of prokaryotic evolution • Archaeabacteria are much closer to eukaryotes than they are to eubacteria • Archaea inhabit extreme environments (hot springs, salt ponds, thermal vents) A thermal vent  p. 503 Cool Harvard Cell Video

  6. Prokaryotic Structure • Most prokaryotes are unicellular • Some species tend to form aggregates • Others form true colonies while few exhibit multicellular characteristics • Nearly all prokaryotes have cell walls external to their plasma membranes • Bacterial walls consist of peptidoglycan (polymer of modified sugars cross-linked with short polypeptides); archaea lack peptidoglycan p. 504 Cool Harvard Cell Video

  7. Average prokaryote diameter: 1 – 5 μm Average eukaryotic diameter: 10 – 100 μm The largest prokaryote: Bacilli measuring ½ mm p. 504 Among pathogens, gram-negative are more threatening because they are more resistant to antibiotics (i.e. penicillin) that degrade peptidoglycan Capsule: sticky protective secretion on prokaryotes that provides protection Gram stains: Gram-positive: simpler walls and abundant peptidoglycan Gram-negative: complex with low peptidoglycan; outer membrane contains lipopolysaccharides (carbohydrate bonded to lipid)

  8. Motility • About half of prokaryotes are motile • Many move through solutions of water, ions, and other solutes • Many motile prokaryotes can move about 50 μm/sec • Flagellar movement • Spirochete movement • Most are capable of taxis (movement toward/away from a stimulus • Magnetic particles establish up and down • Photosynthetic bacteria show positive phototaxis Spirochete p. 506 EubacteriaArchaeabacteria

  9. Cellular and Genomic Organization • Prokaryotes lack the extensive eukaryotic compartmentalization • Bacteria have smaller, simpler genomes • Genophore – prokaryotic chromosome • DNA is concentrated in a snarl of fibers in a nucleoid region • Plasmids may also be present • The prokaryotic ribosome is smaller p. 506 Black Hole in Space

  10. Reproduction and Variation • Binary fission – continuous DNA synthesis and indefinite asexual multiplication • Three methods of genetic recombination: • Transformation – genetic material taken from the environment • Conjugation – genes transferred directly between prokaryotes via sex pilius • Transduction – genes transferred between prokaryotes and viruses • Mutation remains the largest source of variation • Populations of prokaryotes grow and adapt rapidly • Growth in prokaryotes refers to population size more than individual cell enlargement • Some bacteria form resilient cells called endospores around their DNA, encasing it against most degrading elements Variations in endospore morphology (1, 4) – Central endospore (2, 3, 5) – Terminal endospore (6) – Lateral endospore p. 507 Binary Fission

  11. Nutritional and Metabolic Diversity • Photoautotroph – Organisms that harness light energy to drive photosynthesis with CO2 (cyanobacteria) • Chemoautotroph – Organisms that need only CO2 to oxidize inorganic substances with chemical energy from hydrogen sulfide (H2S), ammonia (NH3), and ferrous ions (Fe2+) or other molecules • Photoheterotroph – Organisms that use light to generate ATP, but obtain carbon in organic form • Chemoheterotroph – Organisms that consume organic molecules for both energy and carbon p. 508 The Toba Eruption

  12. p. 508 – 509

  13. Nutritional Diversity Among Chemoheterotrophs • Saprobes: Decomposers that absorb their nutrients from dead organic matter • Parasites: Organisms that absorb their nutrients from body fluids of living hosts • Nitrogen Metabolism • Nitrogen fixation p. 1141 p. 508 – 509 Supernova Explosion

  14. Metabolic Relationships to Oxygen • Obligate aerobes use O2 for cellular respiration and cannot grow without it • Obligate anaerobes are poisoned by O2 which live either exclusively on fermentation or extract chemical energy through anaerobic respiration • Facultative anaerobes will use O2 is it is present but can also undergo fermentation p. 509 Quasar

  15. The Bacteria Song!!! Before we move to some facts…

  16. Fun Facts • Prokaryotes have a higher metabolic rate than eukaryotes due to their large surface area to volume ratio • Cyanobacteria often live in differentiated colonies, showing small signs of specialization • We are made of dead star meterial • Black holes are gravity’s revenge on mass Neptune’s Great Dark Spot

  17. Thank you! Thank you very much!

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