3,5Sep08 - Lecture overview Size and shape of microbes used...

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1 Lecture overview Size and shape of microbes used in classification Envelopes (cytoplasmic/plasma membranes, cell walls, outer membranes, S-layers) Prokaryotic appendages (flagella and pili) Cytoplasmic structures (nucleoid, ribosomes, cytoskeleton and inclusions) Endospores
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2 Shapes of some prokaryotes (Fig. 3.1) Cocci (spherical); bacilli (rod-like);vibrios (comma-shaped); spirilla (spirals) or spirochete (cork-screw); pleomorphic Cells can stick together after dividing to form pairs (diplo), tetrads, chains (strepto), grape-like clusters (staphylo), filaments Sizes range from 0.05 μ m diameter to lengths of > 500 μ m E. coli is typical at 1 x 3 μ m
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Some cell shapes from text (Fig. 3.2) (a) Vibrio cholerae (vibrio, SEM) (b) Rhodospirillum rubrum (spirilla, phase contrast) (c) Leptospira interrogans (spirochete) (d) Actinomyces (filamentous, SEM) (e) Hyphomicrobium (buds) (f) Haloquadratum walsbyi (square Archaea) 3
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4 Parts of bacterial envelope of Gram-positive vs. Gram-negative bacteria (Fig. 3.17) Envelope contains plasma membrane (AKA cytoplasmic membrane; PM or CM); cell wall made of murein (a type of peptidoglycan) and sometimes an S-layer Gram-negative bacteria have also an outer membrane (OM) and periplasmic space (space between CM and OM)
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5 The bacterial plasma membrane (Figs. 3.5-3.7) Basic structure is phospholipid bilayer with integrated hopanoids Lipid composition depends on microbe, environment
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6 Bacterial cell membrane (Brock Fig. 4.14; 4-20) Fatty acids provide barrier to most molecules Special transport systems needed for almost all substances
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7 Bacterial cell wall: Structure of murein (Figs. 3.18, 3.20) Layers of alternating NAG and NAM (lysozyme-sensitive) Each NAM has an attached short peptide that is X-linked to another short peptide on an adjacent NAM (transpeptidase -- inhibited by many antibiotics) Gram-positive bacteria: X-link of D-Ala is to gly interbridge to L-Lys and walls have many layers (20-80 nm) Gram- negative bacteria: No interbridges, use DAP (diaminopimelic acid) and have fewer layers (2-7 nm)
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8 Gram-positive cell wall features (Figs. 3.23, 3.24) Special structures called techoic acids (right) are covalently attached to cell wall (lipotechoic acids to PM) Give overall negative charge to cell wall, but function is unclear All cell walls protect cells from swelling in hypotonic environments
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