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Chapter 3: Microscopy and Cell Structure
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Important Point: If you are having trouble
understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!
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Typical Bacterial Shapes
Also Pleomorphic Bacteria, which vary in their shape (e.g., Corynebacterium).
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Typical Bacterial Arrangements
streptococci sarcina staphylococci
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Prokaryotic Cell Structures
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Typical Prokaryotic Cell
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Movement across membrane for many substances is controlled by membrane proteins.
Escherichia coli has >200 membrane proteins. Many of these proteins are involved in transport across membranes. Others of these proteins allow a bacterium to sense its surrounding environments (e.g., as in chemotaxis). Movement is via: Simple Diffusion (including osmosis) Facilitated Diffusion (with concentration gradient & no energy expended) Active Transport (against concentration gradient & energy expended) Cytoplasmic Membrane
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Simple Diffusion -- Osmosis
solute molecules/ions Simple Diffusion -- Osmosis
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Cytoplasmic Membrane
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Protein-Mediated Transport
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Active Transport
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The Prokaryotic Cell Wall
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The Prokaryotic Cell Wall
Determines cell shape. In some cases recognized by host immune system. Prevents osmotic lysis. Target for antibiotics. In Bacteria, composed of Peptidoglycan. Part of cell envelope.
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Gram-Pos vs. Gram-Neg.
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Gram-Positive Cell Envelope
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Gram-Negative Cell Envelope
endotoxin Gram-Negative Cell Envelope cell wall
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Gram-Negative Cell Envelope
LPS: Protection from antibiotics such as penicillin plus against certain toxins. Periplasm: Site of preliminary nutrient degradation.
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Lipopolysaccharide (LPS)
Carbohydrate has negative charge and provides protection against some antibiotics & some toxins (e.g., detergents). Lipopolysaccharide (LPS) Lipid A = Endotoxin
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Mycoplasma lack Cell Walls
Note: Pleomorphic Mycoplasma lack Cell Walls Mycoplasma pneumoniae causes “Walking Pneumonia”
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Protection (e.g., Streptococcus pneumoniae from phagocytosis)
Glycocalyx Attachment (e.g., Streptococcus mutans causing dental plaques)
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Capsule Staining Capsules are more regular and gelatinous.
Slime Layers are less regular and more diffuse.
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Bacteria Flagella (plural)
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Flagellar Arrangements
Polar Flagellum Flagellar Arrangements e.g., E. coli also “atrichous”
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Also Phototaxis, etc. Chemotaxis
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Pili (sing. Pillus)
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Fimbriae (a kind of pilli)
Tips are Adhesins, used to adhere, e.g., to animal tissues
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Closed Circular Chromosome
Also Plasmids, which are smaller, circular pieces of DNA. Plasmids usually encode expendable functions, e.g., antibiotic resistance.
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Ribosomes: Sites of Translation
On order of 10,000 per cell!
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Endospores Form inside of vegetative cells (hence “endo”).
Characteristic of many soil bacteria, e.g., Bacillus spp. & Clostridium spp. Endospores Highly resistant to heat, U.V., desiccation, etc.
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