Transcript Ch27-1
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 • Prokaryotes often live in symbiotic relationships – endosymbiosis p. 502 - 503 Tornado on the road p. 503 Point of reference 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 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 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 Average prokaryote diameter: 1 – 5 μm Average eukaryotic diameter: 10 – 100 μm The largest prokaryote: Bacilli measuring ½ mm p. 504 Gram stains: Gram-positive: simpler walls and abundant peptidoglycan Gram-negative: complex with low peptidoglycan; outer membrane contains lipopolysaccharides (carbohydrate bonded to lipid) Among pathogens, gramnegative 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 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 Spirochete • Magnetic particles establish up and down • Photosynthetic bacteria show positive phototaxis Eubacteria p. 506 Archaeabacteria 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 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 p. 507 (6) – Lateral endospore Binary Fission 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 p. 508 – 509 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 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 Before we move to some facts… The Bacteria Song!!! 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 Thank you! Thank you very much!