Microscopy & Cell Structure

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    Microscopy and

    Cell Structure

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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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    CytoplasmicM

    embra

    ne

    Movement across membrane for many substancesis controlled by membrane proteins.

    Escherichia colihas >200 membrane proteins. Many of these proteins are involved in transport

    across membranes.

    Others of these proteins allow a bacterium to senseits surrounding environments(e.g., as in chemotaxis). Movement is via:

    Simple Diffusion (including osmosis)

    Facilitated Diffusion (with concentrationgradient & no energy expended)

    Active Transport (against concentrationgradient & energy expended)

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    SimpleDiffusion

    --Osmosis

    solute

    molecules/ions

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    CytoplasmicM

    embra

    ne

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    Protein-

    Mediate

    dTransport

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    ActiveTra

    nsport

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    The Prokaryotic Cell Wall

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    The Prokaryotic Cell Wall

    Determines cell

    shape.

    Prevents osmotic

    lysis.

    In some cases

    recognized by host

    immune system.

    Target for

    antibiotics.

    Part of cell

    envelope.

    In Bacteria,composed of

    Peptidoglycan.

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    Gram-Pos vs. Gram-Neg.

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    Gram-Positive Cell Envelope

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    Gram-NegativeC

    ellEnvelope

    cell wall

    endotoxin

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    Gram-Negative Cell Envelope

    Periplasm: Site

    of preliminary

    nutrientdegradation.

    LPS: Protection from

    antibiotics such as

    penicillin plus againstcertain toxins.

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    Lipopo

    lysaccha

    ride(LPS)

    Lipid A =Endotoxin

    Carbohydrate has

    negative charge andprovides protection

    against some

    antibiotics & some

    toxins (e.g.,

    detergents).

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    Mycoplasmalac

    kCellWalls

    Note:Pleomorphic

    Mycoplasma pneumoniae causesWalking Pneumonia

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    Glycocalyx

    Protection (e.g.,

    Streptococcuspneumoniae from

    phagocytosis)

    Attachment (e.g.,

    Streptococcus

    mutans causing

    dental plaques)

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    Ca

    psuleStaining

    Capsules are moreregular and

    gelatinous.

    Slime Layers are

    less regular and

    more diffuse.

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    Bacteria Flagella (plural)

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    Flage

    llarArra

    ngemen

    ts

    also atrichous

    e.g.,E. coli

    Polar

    Flagellum

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    Chemot

    axis

    Also

    Phototaxis,etc.

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    Pili (sing. Pillus)

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    Closed Circular Chromosome

    Also Plasmids, which are

    smaller, circular pieces of

    DNA.

    Plasmids usually

    encodeexpendablefunctions, e.g.,

    antibiotic

    resistance.

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