27 - Prokaryotes

27 - Prokaryotes - 27.1:Structural,functional,and

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27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success 12:22 Unicellular Diameters: 1-5µm Shapes Sphere (cocci) Rods (bacilli) Spirals Cell Surface Structures **Cell Wall o physical protection o prevents cell from busting in a hypotonic environment water loss inhibits reproduction o contain  peptidoglycan a network of modified-sugar polymers croo-linked by short poply  peptides encloses entire bacterium anchors other molecules that extend from surface Gram stain:  classifies many bacterial species into 2 groups o Gram-positive
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Simpler walls  Large amt of peptidoglycan o Gram-negative Less peptidoglycan Structurally more complex Outer membrane: lipopolysaccharides Often toxic Protects bacteria against body’s defenses More threatening More resistant to antibiotics Certain antibiotics derives from their inhibition of the peptidoglycan cross- linking o Prevent formation of functional cell wall Covered by  capsule o A sticky layer of polysaccharide / protein o Enables prokaryotes to adhere to their substrate / other individuals o Shield pathogenic prokaryotes from attacks by host’s immune system o Hairlike appendages
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o Fimbriae shorter and more # o Sex pili  specialized for exchange of DNA Motility ½ capable of directional movement flagella o scattered over entire surface / concentrated at one/both ends o 1/10 of eukaryotic flagella o environment uniform » may move randomly heterogeneous » many exhibit  taxis movement toward / away from stimulus chemotaxis: respond to chemicals by changing movement  pattern toward: positive away: negative Lack complex compartmentalization Some have specialized membranes the perform metabolic functions o Usually infoldings of plasma membrane o Aerobic prokaryote o Photosynthetic prokaryote Cyanobacteria
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1/1000 of eukaryotic DNA o ring of DNA =   prokaryotic chromosome o nucleoid region:  Part of cytoplasm that is lighter in microscope; where  DNA is o plasmids:  smaller rings of DNA consisting of only few genes provide resistance to antibiotics direct metabolism of rarely encountered nutrients have other such “contingency” functions  chance of survival
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27 - Prokaryotes - 27.1:Structural,functional,and

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