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Chapter 27 Bacteria and Archaea

Chapter 27 Bacteria and Archaea - Chapter 27 Bacteria and...

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Chapter 27: Bacteria and Archaea 27.1: Structural and functional adaptations contribute to prokaryotic success - The first organisms thought to inhabit Earth ar e prokaryot es - Most are unicellular although they m ay a ggregat e te m porarily or per m an ently in colonies - They are usually 0.5-5 μ m in size - The three m ost com m on shap es are sph eres (cocci), rods (bacilli), a nd spirals Cell Surface Structures - Nearly all prokaryotic cells have a cell wall o Maintain cell shap e o Provide physical protection o Prevents the cell from bursting in a hypotonic environm ent o Contain p eptidoglycan rather than chitin or cellulose - Peptidoglycan: a network of m odified-sug ar polym ers cross-linked by short polypeptides o Encloses the entire bact erium and anchors other m olecules that ext end from its surface o Archa e al cell walls have a variety of polysaccharides a nd proteins but lack p eptidoglycan - Gra m st ains o Developed by 19 th century Hans Christian Gram to classify bacteria based on cell wall composition Valuable tool for determining what kind of treatment is appropriate o Gram positive bacteria have simpler walls with a relatively large amount of peptidoglycan Ex: Mycobacterium tuberculosis , causes tuberculosis More vulnerable to antibiotics Antibiotics work by inhibiting peptidoglycan cross-linking, resulting in a dysfunctional cell wall o Gram negative bacteria have less peptidoglycan and are structurally more complex, with an outer membrane that contains lipopolysaccharides Lipid portions of the lipopolysaccharides are toxic, causing fever or shock Outer membrane protects it from the body’s defenses It also makes it more resistant to antibiotics - Capsules cover the cell wall of m a ny prokaryotes o A sticky layer of polysaccharide or protein that e n a bles prokaryotes to a dh ere to their substrat e or to e ach other o Also protects ag ainst d ehydration o Can shield from att acks by im mun e syste m - Fimbriae: h air-like protein app end ag es that allow so m e prokaryotes to cling to e ach other or to their substrat e o Also known a s att ach m ent pili o Usually shorter a nd m ore nu m erous than sex pili (used to pull two cells together prior to DNA transfer) Motility - Flagella m ay b e scatt ered over the e ntire surface or the cell or concentrat ed at one or both ends o Not covered by an ext ension of the plas m a m e m bran e and are 1/10 the width of e ukaryotic flagella o Different from e ukaryotes in ter ms of m olecular com position and m ech anism of propulsion - Flagellated prokaryotes m ay m ove rando mly in a relatively uniform environ m ent - In a het erogen eous environ m e nt, they m ay exhibit a taxis Internal a nd Geno mic Organization - Prokaryotes lack the internal com p art m e nt alization of eukaryotic cells
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