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Prokaryotes (Archaea and Bacteria) Chapter 28 The First Cells Microfossils are fossilized forms of microscopic life -Oldest are 3.5 billion years old -Isotopic analysis and concentration of carbon-12 in fossils suggests that carbon fixation was active as much as 3.8 BYA 2 The Cyanobacteria Stromatolites are mats of cyanobacterial cells that trap mineral deposits -Oldest are 2.7 billion years old -Lipids were found in ancient rocks 3 4 Flagella, spin like propellers Composed of the protein flagellin 5 Prokaryotic Features Metabolic diversity -Two types of photosynthesis -Oxygenic = Produces oxygen -Anoxygenic = Nonoxygen producing - E.g: Sulfur and sulfate -Chemolithotrophic prokaryotes derive energy from inorganic molecules 6 Bacteria vs. Archaea Plasma membrane -Bacterial-Connected to glycerol by ester linkages -Archaeal-Connected to glycerol by ether linkages 7 Prokaryotic Shapes Most prokaryotes have one of 3 basic shapes -Bacillus = Rod-shaped -Coccus = Spherical -Spirillum = Helical-shaped 8 The Bacterial Cell Wall Maintains shape and protects the cell from swelling and rupturing Consists of peptidoglycan -Polysaccharides cross-linked with peptides Cell wall is the basis of the Gram stain 9 The Bacterial Cell Wall Two main types -Gram-positive bacteria -Thick peptidoglycan -Teichoic and lipoteichoic acids -Gram-negative bacteria -Thin peptidoglycan -Have an outer membrane -Contains lipopolysaccharide 10 The Bacterial Cell Wall 11 The Bacterial Cell Wall 12 Internal Structure Internal membranes -Invaginated cell membrane -For respiration or photosynthesis Endospores -Highly-resistant structures -Released upon cell lysis -Can germinate back to normal cell 13 Prokaryotic Genetics Prokaryotes do not reproduce sexually However, they undergo horizontal gene transfer, which is of three types -Conjugation = Cell-to-cell contact -Transduction = By bacteriophages -Transformation = From the environment 14 Conjugation Transfer of the F plasmid occurs through the conjugation bridge The end result is two F+ cells -R (antibiotic resistance) plasmids 15 -Virulence plasmids (E. coli O157:H7 strain) Transduction Viruses package bacterial DNA and transfer it in a subsequent infection 16 Transformation Natural transformation -DNA that is released from a dead cell is picked up by another live cell...Horizontal gene transfer (no cell fusion so not sexual17 !!) Prokaryotic Metabolism Acquisition of Carbon -Autotrophs = From inorganic CO2 -Heterotrophs = From organic molecules Acquisition of Energy -Chemolithotrophs = From inorganic chemicals -Phototrophs = From sunlight 18 Prokaryotic Metabolism Photoautotrophs -Cyanobacteria Chemolithoautotrophs -Nitrifiers Photoheterotrophs -Purple and green nonsulfur bacteria Chemoheterotrophs -Majority of prokaryotes -Use organic molecules for C and energy 19 Prokaryotic Metabolism Type III secretion system -Found in many Gram-negative bacteria -Used to transfer virulence proteins directly into host cells -Yersinia pestis – Bubonic plague -Pseudomonads – Plant pathogens -Blights, soft rot, wilts 20 Human Bacterial Disease Tuberculosis -Mycobacterium tuberculosis -Afflicts the respiratory system -Mutidrug-resistant (MDR) strains are very alarming 21 Human Bacterial Disease Dental caries (tooth decay) -Plaque consists of bacterial biofilms -Streptococcus ferments sugar to lactic acid -Tooth enamel degenerates Peptic ulcers -Helicobacter pylori is the main cause -Treated with antibiotics 22 Sexually transmitted diseases (STDs) Gonorrhea -Neisseria gonorrhoeae -Can pass from mom to baby via birth canal -Can cause pelvic inflammatory disease (PID) Chlamydia -Chlamydia trachomatis -Can cause PID and heart disease 23 Beneficial Prokaryotes Prokaryotes are crucial to chemical cycles -Decomposers release a dead organism’s atoms to the environment -Photosynthesizers fix carbon into sugars -Nitrogen fixers reduce N2 to NH3 (ammonia) 24 Beneficial Prokaryotes Bacteria are used for bioremediation -Remove pollutants from water, air and soil 25 -Exxon Valdez oil spill