Lecture16 - 3/18/11 Lecture 16 The Background Biology of...

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3/18/11 1 Lecture 16 The Background Biology of Bacteria Time-Line for the Origin of Life ~15 bya - Big Bang! ~4.7 bya - Solar system forms ~4.5 bya - Formation of Earth What happened here? ~3.5 bya - First fossils on Earth The First Bacteria? • Stromatolites (3.5 bya) • Fossilised cells (3.5 bya) • Earliest fossils (Archean age) are from Western Australia. • More recent analysis has cast serious doubt on these “fossils”; are they simply carbonaceous formations, produced by the scalding action of water on minerals? (Brasier et al . Nature 416 , 76-81; 2002).
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3/18/11 2 • Cyanobacteria are larger than most bacteria, and may secrete a thick cell wall. Cyanobacteria may form large layered structures, called stromatolites. • Stromatolites form as a mat of cyanobacteria grows in an aquatic environment, trapping sediment and sometimes secreting calcium carbonate. Short chain of cyanobacterial cells, from the Bitter Springs Chert of northern Australia (~1 billion years old). Modern cyanobacteria Fossil Cyanobacteria Fungi Plants Animals Crenarchaeota Euryarchaeota Archaea Bacteria Eukaryotes The rRNA “Tree of Life” Root? Phylogeny of Bacteria • Daubin et al . Genome Research 12 , 1080-1090 (2002).
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3/18/11 3 Gram+ and Gram- Bacteria Gram staining exploits the differential binding to the bacterial cell wall of a dye (crystal violet) and iodine. Gram+ organisms retain the purple colour after washing with acetone, while Gram- organisms lose the colour and appear pink when counter-stained with neutral red. Gram+ bacteria have a thick peptidoglycan layer external to the celll membrane, whereas Gram- bacteria have a thin layer. Phylogenetically distinct groups. Gram + Thicker cell wall Teichoic Acids Gram - Endotoxin - Lipopolysaccharide (LPS) Characteristic Features of Bacteria & Archaea Compared to Eukaryotes • Bacteria & archaea lack membrane-bound nuclei and organelles, and have a single circular chromosome. • Bacteria & archaea lack spliceosomal introns. • Archaea and eurkaryotes have multiple complex RNA polymerases and begin translation with methionine. Bacteria begin translation with formyl-methionine. • Unique features of archaea: - cell walls vary in structure, but always lack the peptidoglycan of bacterial cell walls. - the lipids in their membranes are branched and have ether linkage to glycerol. - presence of large signal recognition RNA. Types of Intron • Spliceosomal introns (or ‘nuclear’ introns): - spliced by a spliceosome (proteins & RNA) - only found in “higher eukaryotes” • Protein-spliced introns: - found in rRNA and tRNA genes • Self-splicing introns (Group I, Group II, Group III): - use the autocatalytic properties of RNA to splice - found in scattered mitochondria, chloroplasts, bacteria and protist eukaryotes
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3/18/11 4 Biodiversity of Bacteria Size of Bacteria • Average bacteria is 0.5 - 2.0 υ m in diameter • Average surface area (SA) ~12 υ m 2 • Average volume is ~4
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Lecture16 - 3/18/11 Lecture 16 The Background Biology of...

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