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AP Biology, Chapter 27 Prokaryotes and the Origins of Metabolic Diversity Summary Introduction THE WORLD OF PROKARYOTES They're (almost) everywhere an overview of prokaryotic life 1. Describe the many unique characteristics of prokaryotes. Explain why it might be said that prokaryotes are the most successful organisms ever to live. a. Most ancient, small, anucleate b. Only major taxon found everywhere, in all environments c. Most numerous 2. Describe the impact of prokaryotes on humans and biological ecosystems. a. A minority cause disease b. Most are decomposers, some recycle nutrients in biogeochemical cycles c. Many form beneficial symbiotic relationships d. Origin of mitochondria and chloroplasts Bacteria and archaea are the two main branches of prokaryote evolution 3. Describe the classification of the archaea and the bacteria in the three-domain system. a. Archaea separated by rRNA sequence and genome structure b. Archaea inhabit extreme enevironments: acid, salt, hot c. Molecular studies suggest Archaea and Eukarya share a more recent common ancestor d. Prokaryote is a paraphyletic construction STRUCTURE, FUNCTION, AND REPRODUCTION OF PROKARYOTES Introduction 4. Describe the general size, organization, and specialization of prokaryotic organisms. a. Size 1-5 micrometers b. Unicellular with a few colonial types c. Rod-shaped bacilli; spherical cocci; spiral spirilli and spirochetes Nearly all prokaryotes have cell walls external to their plasma membranes 5. Describe the structure, composition, and functions of prokaryotic cell walls. a. Nearly all have a cell wall with peptidoglycan b. Functions include shaping, osmotic protection, physical protection c. Major differences: Gram + and gram 6. Distinguish between the structure and staining properties of gram-positive and gramnegative bacteria. Explain why disease-causing gram-negative bacterial species are generally more pathogenic than disease-causing gram-positive bacteria. a. Gram i. Light pink in gram stain ii. Thin peptidoglycan with second membrane and lipopolysaccharide (LPS) iii. Generally more pathogenic iv. Incl. Salmonella and E. coli b. Gram + i. Deep violet in gram stain ii. Thick peptidoglycan with no second membrane or LPS iii. More susceptible to lysozyme and penicillin; both act on peptidoglycan iv. Incl. Bacillus sp. Many prokaryotes are motile 7. Describe three mechanisms that motile bacteria use to move. Explain how prokaryotic flagella work and why they are not considered to be homologous to eukaryotic flagella. a. Three mechanisms i. Stiff protruding flagella that twirl ii. Flagella around which the cell is coiled; corkscrews through liquid iii. Gliding on secreted material b. Protruding flagella i. Not homologous: no membrane, no force generated within flagella ii. Stiff flagella are twirled my a motor embedded in the membrane/wall; energy from proton gradient c. Allows movement (taxis) in response to various stimuli The cellular and genomic organization of prokaryotes is fundamentally different from that of eukaryotes 8. Explain how the organization of the prokaryotic genome differs from that in eukaryotic cells. a. No nuclei; circular chromosome wound into a wad b. 1/1000 the size of a eukaryotic chromosome; mostly coding c. Small accessory plasmids may be present Populations of prokaryotes grow and adapt rapidly 9. List the mechanisms that are sources of genetic variation in prokaryotes and indicate which one is the major source. a. Mechanisms of exchange: transformation, transduction, conjugation b. Major source: new mutation 10. Describe growth as it applies to prokaryotes. Explain what is meant by geometric growth. a. Growth is mainly in numbers, not size b. Geometric = exponential = 124816, etc. 11. Describe the functions of endospores. a. Endospores are dormant, thick-walled cells b. Resistant to heat, drying, digestion, poisoning 12. Describe the natural adaptive advantage of antibiotics. a. Microorganisms produce antibiotics to kill competing cells b. Antibiotic-producers have some mechanism of resistance NUTRITIONAL AND METABOLIC DIVERSITY Introduction Prokaryotes can be grouped into four categories according to how they obtain energy and carbon 13. Distinguish between photoautotrophs, chemoautotrophs, photoheterotrophs, chemoheterotrophs, saprobes, and parasites. Give examples of each. a. Photoautotrophs i. Light energy; CO2 for carbon ii. Cyanobacteria with chlorophyll a, plants, algae, and photosynthetic bacteria b. Chemoautotrophs i. Inorganic compounds for energy; CO2 for carbon ii. Purple sulfur bacteria c. Photoheterotrophs i. Light energy; organic compounds for carbon ii. Purple non-sulfur bacteria d. Chemoheterotrophs i. Organic compounds for energy and carbon ii. Animals, fungi, a few plants, many bacteria e. Saprobes i. Chemoheterotrophs feeding on dead organisms ii. Include most fungi and bacteria f. Parasites i. Chemoheterotrophs feeding on live organisms ii. Infectious diseases 14. Describe the process and explain the significance of nitrogen fixation. a. N-fixation = conversion of N2 gas into NH3 by chemoautotrophic bacteria and photoautotrophic cyanobacteria b. Other bacteria covert ammonia to nitrites (NO2-) and nitrates (NO3-) c. Nitrites and nitrates are usable by plants d. Denitrifying bacteria convert NO2- and NO3- back to N2 15. Distinguish among obligate aerobes, facultative anaerobes, and obligate anaerobes. a. Obligate aerobes require oxygen for growth b. Facultative anaerobes can use oxygen but don't need it c. Obligate anaerobes are killed by oxygen The evolution of prokaryotic metabolism was both cause and effect of changing environments on Earth 16. Describe, with supporting evidence, plausible scenarios for the evolution of metabolic diversity, including the: a) nutrition of early prokaryotes, b) origin of electron transport chains, c) origin of photosynthesis, d) origin of aerobic respiration. a. Early prokaryotes i. ATP and glycolysis appeared early since they are universal ii. No oxygen; therefore, anaerobes iii. 5th edition: little organic material; therefore, first came chemoautotrophs iv. 6th edition: enough organic material; therefore, first came chemoheterotrophs b. Electron transport i. Chemoautotrophy may have yielded H 2 + energy ii. Energy may have split H2 giving a proton gradient + free electrons iii. Membranes capable of manipulating H/electrons would have been favored c. Photosynthesis i. Pigments may have protected from UV ii. Energized pigments on membranes may have linked with electron transport/ATP generation iii. Archaea use bacteriorhodopsin to generate ATP iv. Cyanobacteria have both photosystems and generate O2 d. Aerobic respiration/oxidative phosphorylation/Krebs cycle i. Abundant H2O is an advantageous electron donor for photosynthesis ii. O2 released killed many, some acquired oxygen toleration mechanisms iii. O2 would have been useful as an electron acceptor iv. Purple nonsulfur bacteria use a part photosynthesis electron transport chain for aerobic respiration PHYLOGENY OF PROKARYOTES Introduction Molecular systematics is leading to a phylogenetic classification of prokaryotes 17. Explain how molecular systematics has been used in developing a moneran classification. Explain why clinical phenotypes are a poor guide to phylogeny. a. Little fossil evidence and very simple morphologies; rRNA is more useful b. Clinical phenotypes i. Shape, gram stain, motility, nutrition ii. Good for practical ID of common pathogens iii. Most are polyphyletic 18. Describe the distinguishing features and give examples of the methanogens, extreme halophiles, and extreme thermophiles. Explain why these groups are collectively known as extremeophiles. a. Archaean clades are based solely on comparison of rRNA sequences b. Major non-clade types i. Methanogens oxidize H2 using CO2 to produce CH4 in intestines and rotting material ii. Halophiles thrive in unusually salty environments; some contain bacteriorhodopsin iii. Thermophiles withstand high temperatures c. Archaeans are much more pervasive than the label "extremeophile" implies ECOLOGICAL IMPACT OF PROKARYOTES Introduction Prokaryotes are indispensable links in the recycling of chemical elements in ecosystems 19. Describe the role of prokaryotes in recycling within ecosystems. a. Prokaryotic decomposers release essential nutrients from dead organisms b. Others convert essential nutrients into usable forms c. Others replenish the "starting" forms Many prokaryotes are symbiotic 20. Distinguish among mutualism, commensalism, and parasitism. Describe examples of prokaryotes in each of these relationships. a. Mutualism i. Close association in which both benefit ii. Intestinal flora completes digestion, makes vitamins iii. Nitrogen fixing bacteria live in legume root nodules b. Commensalism i. One benefits, the other is neutral ii. Most bacteria on and in humans are commensals c. Parasitism i. One benefits, one is harmed ii. Bacterial diseases like tuberculosis, leprosy, and anthrax 21. List Koch's postulates, which are used to substantiate a specific pathogen as the cause of a disease. a. Find the suspected pathogen in each individual with the disease b. Isolate it from a diseased individual and grow it in the laboratory c. Cause the disease by infecting from the culture d. Re-isolate the pathogen from the experimental infection Humans use prokaryotes in research and technology 22. Distinguish between exotoxins and endotoxins and describe examples of each. a. Exotoxin i. Toxic substances secreted by pathogens ii. Ex.: Clostridium botulinum makes botulinum toxin iii. Ex.: Vibrio cholerae makes cholera toxin b. Endotoxin i. Toxic substances that are part of the cell wall/membrane ii. Ex.: lipopolysaccharide in Salmonella 23. Describe how Streptomyces can be used commercially. a. Production of many useful antibiotics 24. Describe the limitations of antibiotics in combating bacterial diseases. a. Bacteria microevolve resistance b. We're running out of easily assessed microbiodiversity 25. Describe how humans exploit the metabolic diversity of prokaryotes for scientific and commercial purposes. a. "Simple" microbes like E. coli are exhaustively studied b. Fermentation makes food and medicines c. Bacteria may help break down pollutants