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TAMU BIOL 112 - CH27

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Chapter 27 Bacteria and ArchaeaProkaryote StructureUnicellular- But some stay joined in groups, chains or clusters after fission- Size- mostly 1-5 nanometersCommon Shapes- Rods- bacillus, bacilli- Spheres- coccus, cocci- Spiral- spirilla, spirocheteCell SurfaceCell wall outside plasma membrane- Prevents cell rupture in hypotonic environments- Bacterial walls have peptidoglycan- Archaea walls are diverse but do not have peptidoglycan- Gram-Satin reflects wall typeo Gram + are bacteria with a thick peptidoglycan layer. They show purple under the microscope because the stain is not washed outo Gram – are bacteria with a thinner peptidoglycan layer and outer membrane. They show pink under the microscope. They are often toxic and resistant to drugs.- Sticky capsule (often) outside cell wallo Adheres (glues) cells together and to the surfaceo Resists attack from immune systemo Holds in moisture- Hair like Fimbriaeo Helps cells stick to surfaces and each other- Sex pilluso Pulls two bacteria together for DNA transfer (conjugation) Forms mating bridgeMotilityTaxis is the movement toward or away from stimuli- Chemotaxis- Phototaxis- Geotaxis (magnetotaxis)- use metal to orient and move- Many move using rotating flagella (the best studied method)o Not at all like eukaryotic flagellao H+ ions flow through a protein motor, creating a gradient, and causing a distortion of proteins. This distortion causes rotation.Internal organization- There are no membrane bound organelles- Some have in folded plasma membranes o Used for aerobic cellular respiration and photosynthesis Similar to mitochondria and chloroplasts- Nucleoid is the region with DNAo One circular DNA molecule with fewer binding proteins than eukaryotes- Plasmids are independent tiny rings of DNAo They add genetic diversityGenetic DiversityCell Reproduction and Diversity- Binary fission yields two identical cells (review 12.12)o There is a short generation timeo Geometric growth in numbers (1, 2, 4, 8…)o Under stress, some species divide to form and endospore Resists heat, drought, etc. for years- Mutations do in increase genetic diversityo Mutations are rare per division (1:107)o But high rate of cell division leads to many mutationso Each new mutation is passed on (cloned)o Mutation can change the phenotype- Prokaryotes can evolve rapidlyo See experiment 27.10o Began with one strain using “good” mediumo Generations grow on “poor” mediumo Only source of new diversity was mutation This allowed for natural selectionRecombination by transformation- See Griffith’s experiment Fig 16.2- DNA bits from ruptured donor cells absorbed directly be recipient- DNA with new homologous alleles transfers into chromosomes (recombinant)Recombination by Transduction- Bacteriophage virus carries DNA from “donor” to recipient strain- Adds new chromosomal alleles to recipient cell (recombination)Recombination by Conjugation- Requires presence of F Factor in the donor o Located in F plasmid in the chromosomeo F Factor gene build sex pilus- F plasmid conjugationo From F+ donor to a F- recipiento F- cell becomes F+ cell- Hfr cell conjugationo High frequency recombinationo Donor’s F Factor is a part of the chromosomeo F- cell gets new chromosomal alleles but not the F+ allele- R Plasmid Conjugationo R plasmids carry genes that  Confer resistance to antibiotics Build pillio R plasmid conjugation accounts for rapid spread of resistance.Nutritional and Metabolic DiversityProkaryote Nutritional Modes (table 27.1) - The carbon source gives organisms’ biomass.- Autotrophs- carbon source is self-reliant but they still need an energy sourceo Inorganic carbon can be made organic (self-feeders)o Energy source is light or inorganic chemicals (very rare)- Heterotrophso C source is organic compounds produced by other living thingso E source is light (very rare) or organic compoundsOxygen and Metabolism- Obligate aerobes must have oxygen for all respiration- Obligate anaerobes are poisoned by oxygeno Ex Tetanus- Facultative anaerobes can use oxygen for cellular respiration or switch to anaerobic processes if no oxygen is presentNitrogen and Metabolism- Nitrogen is a crucial nutrient in proteins (amino acids) and DNA (nitrogenous bases)o 78% of air is N2 gas But it can’t be used as a gas by organisms because it is inert Most cells need nitrogen as ammonium (NH4+) or nitrides or nitrates- Nitrogen fixation converts N2 to NH4+o Almost all of life’s nitrogen comes from nitrogen fixating prokaryotes (no eukaryotes)o It also comes from lightning and volcanoes- Other prokaryotes convert and cycle nitrogen compounds in the “Nitrogen Cycle” (see 55.14)Metabolic cooperation- Better growth together than alone- Function as a colony or group better than on their owno Cyanobacteria and heterocyst and photosynthetic cellso Biofilms (plaque) are made up of multiple species.Prokaryote Ecological RolesFood Webs and Nutrient Cycling- Primary produces (cyanobacteria) create most of the biomasso Autotrophs “fix” CO2 into organic carbon This is an important base for aquatic food webs- Decomposerso Heterotrophs break down dead material/waste Release carbon dioxide and nutrients (N, P, K) The MOST important decomposers on earth are bacteriaSymbiosis is two species living in a close relationship- Parasitism- smaller parasite benefits at the expense of the other species (host)- Commensalism- one species benefits without any impact (good or bad) on another specieso Most bacteria on our skin- Mutualism- both species benefit from each othero Bacteria in our colon make vitamin Ko Rhizobium in legume roots get sugar and water and provide nitrogen fixation to the planto Flashlight fish have a pocket on their cheek for bioluminescent bacteria to live. They flash it at predators and use it to attract food.Prokaryotes and HumansPathogenic Bacteria- Bacterial toxinso Exotoxins are secreted out from the bacteria They are toxic even the bacteria is dead Botulism bacteriao Endotoxins come from the outer membrane of Gram- bacteria - Antibiotics kill bacteria cells but not eukaryotic cellso Penicillin- Immunization prepares immune system to resist some bacterial diseaseso Bacterial Meningitis, typhoidBeneficial Uses of prokaryotes- Basic research on cells and DNA- DNA technology and genetic engineering- Commercial chemicals and


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TAMU BIOL 112 - CH27

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