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Chapter 28

Chapter 28- Bacteria and archaea.docx

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Fiona Rawle

Chapter 28- Bacteria andArchae 13 12 14 -10 trillion (10 ) cells in body.10 bacterial cells on skin, 10 bacterial and archaeal cells in stomach and intestines. -Soil is very abundant in bacteria and archae cells. -Group 1 (marine archae) may be the most successful organism. -Total number of bacteria and archae alive today approx. 5x100 Bacteria Archae Eukarya Nuclear envelope No No Yes Circular chromosome Yes but linear in some Yes No DNAassociated with No Yes Yes histone proteins? Organelles present Some in limited species No Yes Flagella present? Yes; spin like propeller Yes; spin like bacterial Yes; undulate back and flagella, but distinctive forth and have in molecular completely different composition molecular composition compared with bacteria and archae Unicellular or Almost all uni All uni Many multi Multicellular? Sexual reproduction No Not known Common Structure of lipids in Glycerol bonded to Glycerol bonded to Glycerol bonded to plasma membranes straight-chain fatty acidsbranches fatty acids straight-chain fatty acids via ester linkage (synthesized from via ester linkage isoprene subunits) via ester linkage Cell wall material Almost all contain Varies widely among When present, usually peptidoglycan which species but no made of cellulose or contains muramic acid peptidoglycan and chitin muramic acid Transcription and One relatively simple One relatively complex Several relatively Translation Machinery RNApolymerase; RNApolymerase; complex RNA translation begins with translation begins with polymerases; translation formylmethionine; methionine begins with methionine translation poisoned with several antibiotics that do not affect archae or eukaryotes 28.1Why do Biologists Study Bacteria andArchae? - Some bacteria cause disease- called pathogenic/pathogens. Robert Koch hypothesized bacteria might be responsible for causing infectious disease, which spread by being passed from an infected person to an uninfected person. To form link between specific microbe and disease, Koch proposed 4 criteria be met (Koch’s postulates): 1. Microbe must be present in individuals suffering from disease and absent in healthy ones. 2. The organism must be isolated and grown in a pure culture away from host 3. If organisms from the pure culture are injected into healthy individual, symptoms of disease should appear. 4. The organism should be isolated from the diseased experimental organism, again grown in culture, and demonstrated by its size, shape and color to be the same as original animal. -Germ theory of disease: infectious disease is caused by bacteria and viruses. -antibiotics: molecules that kill bacteria Bacteria can clean up pollution: Bioremediation: the use of bacteria and archae to degrade pollutants. Often based on complementary strategies: 1. Fertilizing contaminated sites to encourage the growth of existing bacteria and archaea that degrade toxic compounds. 2. “Seeding,” or adding, specific species of bacteria and archaea to contaminated sites. Extremophiles: Bacteria and archaea that live in high-salt, high-temperature, low-temperature, or high- pressure environments. Likely that they were first forms of living things on Earth. Studying them might lead to how life on Earth began. Model organisms in extraterrestrial research. If organisms living under profound conditions on earth, more might exist in other planets and moons. Useful in industrial processes because contains enzymes that function in extreme conditions. How do small cells affect global change? - Bacteria and archae have altered the composition of the oceans, atmosphere, and terrestrial environments for billions of years. The Oxygen Revolution -No O2 existed for 2.3 billion years. Dominated by nitrogen and carbon dioxide 1. There was no plausible source of oxygen at the time the planet formed. 2. The oldest Earth rocks indicate that for many years afterward, any oxygen that formed reacted immediately with iron atoms to produce iron oxides. Cyanobacteria: Photosynthetic bacteria. First became numerous in oceans 2.7-2.55 bya. 2.3-2.1 bya oxygen levels begin to increase; common in oceans and cells could begin to use it as the final electron acceptor during cellular respiration. -The evolution of aerobic respiration was a crucial event in the history of life. Because oxygen is extremely electronegative, it is an efficient electron acceptor. Much more energy is released as electrons move through electron transport chains with oxygen as the ultimate acceptor than is released with other substances as the electron acceptor. -Once oxygen levels had built up, macroscopic algae, first eukaryotes began to appear. The Nitrogen Cycle -Plant growth is limited by availability of nitrogen. -Only organisms capable of converting N to am2onia are bacteria. Called nitrogen fixation (redox) Nitrate Pollution Figure 28.7 28
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