1. Prokaryotic Cell Structure 1 Chapter 3: Cellular Structure 1. Prokaryotic Cell Structure 2....

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Transcript of 1. Prokaryotic Cell Structure 1 Chapter 3: Cellular Structure 1. Prokaryotic Cell Structure 2....

  • 9/1/2016

    1

    Chapter 3:

    Cellular Structure

    1. Prokaryotic Cell Structure

    2. Eukaryotic Cell Structure

    1. Prokaryotic Cell Structure

    A. Cell Shape

    B. External Structures

    C. Internal (Cytoplasmic) Structures

    A. Cell Shape

    Chapter Reading pp. 322-325

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    Prokaryotic Cell Shape

    One convenient characteristic with which to

    identify and classify prokaryotes is their

    size and shape as seen in the microscope.

    the diameter of prokaryotic cells ranges from

    ~0.2 to 2.0 mm

    prokaryotes are essentially unicellular and more

    or less maintain a constant shape (monomorphic)

    most prokaryotes have a spherical, rod-shaped

    or spiral appearance though other shapes exist

    as well

    Spherical Cells spherical prokaryotes are

    referred to as cocci(singular = coccus)

    diplo- = found in pairs

    different kinds of cocci

    exhibit characteristic

    arrangements:

    strepto- = found in chains

    staphylo- = irregular clusters

    tetrad = group of 4

    sarcina = cube structure of 8

    Rod-Shaped

    Cells rod-shaped prokaryotes

    are referred to as bacilli(singular = bacillus)

    also found in various

    arrangements:

    diplo- = length-wise pairs

    strepto- = length-wise chains

    cocco- = rounded bacilli

    palisade = bacilli side by side

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    Curved or Spiral Cells

    vibrio = curved rod

    spirillum = twisted rod

    spirochete = corkscrew

    rod

    B. External Structures

    Chapter Reading pp. 59-71

    Prokaryotic Cell Structures

    Ribosome

    Cytoplasm

    Nucleoid

    Glycocalyx

    Cellwall Cell

    membrane

    Flagellum

    Inclusions

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    Head, whichcontainsphosphate (hydrophilic) Phospholipid

    Tail (hydrophobic)

    Phospholipidbilayer

    Integral protein

    Peripheralprotein

    Integralglycoprotein

    Cytoplasm

    Integral proteins

    true barrier between

    internal & external

    phospholipid content is a bit different compared to eukaryotes

    Plasma Membrane

    Cytoplasm

    Diffusionthrough thephospholipid bilayer

    Facilitateddiffusion through a nonspecific channel protein

    Facilitated diffusion through a permease specific for one chemical; binding of substrate causes shape change in channel protein

    Osmosis, the diffusion of water through a specific channel protein or through a phospholipid bilayer

    Extracellular fluid

    Diffusion & Osmosis

    Cell exterior (extracellular fluid)

    Integralprotein

    Protein

    Cell interior (cytoplasm)

    DNA

    Cytoplasmic membrane

    Na+

    Cl

    Protein

    Concentration Gradients

    Different concentrations

    of ions inside vs outside

    the cell are set up &

    maintained by :

    Creates a net negative

    charge inside vs outside.

    protein pumps

    active transport from

    low to high conc.

    protein channels &

    transport proteins

    facilitated diffusion

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    Glucose N-acetylglucosamineNAG

    N-acetylmuramic acidNAM

    repeating disaccharidebackbone

    tetrapeptide(amino acid)crossbridge

    connecting chainsof amino acids

    Bacterial Cell Wall

    The bacterial cell wall provides structure & support:

    main component is a structure called peptidoglycan

    polypeptide-linked

    chains of a repeating

    disaccharide

    (protects cell from

    osmotic lysis!)

    Cells without a wall

    (e.g., mycoplasmas,

    animal cells)

    Cells with a wall

    (e.g., plants, fungal

    and bacterial cells)

    H2O

    H2O

    H2O

    H2O

    H2OH2O

    Cell

    wall

    Cell membrane

    Cell

    wall

    Cell membrane

    Isotonic

    solution

    Hypertonic

    solution

    Hypotonic

    solution

    Osmosis & Cell Lysis

    Peptidoglycan layer of cell wall

    Lipopolysaccharide

    (LPS)

    Outermembraneof cell wall

    Cell membrane

    n

    O side chain(varies inlength andcomposition)

    Gram-negative cell wall

    Lipid A(embeddedin outermembrane)

    Fatty acid

    Porin

    (sectioned)

    Periplasmic space

    Phospholipid layers

    Integral

    proteins

    Corepolysaccharide

    Porin

    thin layer of peptidoglycan

    Gram-negative Cell Wall

    outer membrane containing

    lipopolysaccharide (LPS)

    Lipid A (endotoxin) + polysaccharide

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    Peptidoglycan layer(cell wall)

    Cell membrane

    Teichoic acid

    Integralprotein

    Lipoteichoic acid

    Gram-positive cell wall

    Gram-positive Cell Wall

    thick-layered peptidoglycan cell wall w/teichoic acids

    NO outer membrane

    Bacterial Glycocalyx (sugar cup)Outermost layer that surrounds the bacterium

    called a slime layer if loosely attached, water soluble

    called a capsule if compact, tightly attached to cell wall

    mediates

    adhesion,

    biofilm

    formation

    protects from

    dessication,

    phagocytosis

    Bacterial Flagellum

    basal body,

    hook &

    filament

    basal body

    anchors

    flagellum in

    PM, cell wall,

    rotates hook

    & filament to

    propel

    bacterium

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    Tumble

    Run

    Tumble

    Run attractant

    Flagella & Bacterial Motility Bacteria undergo taxis, i.e. movement in response to

    something.

    e.g., chemotaxis (movement in response to a chemical substance)

    Involves random runs & tumbles:

    longer runs, less tumbles in direction of good stuff

    (RUN = flagella rotate

    counterclockwise)

    (TUMBLE = clockwise)

    Axial

    Filament

    Bundle of

    endoflagella

    found in

    spirochetes

    anchored at one

    end of cell and

    rotate in unison

    rotates cell like

    a corkscrew to

    propel it forward

    Fimbriae & Pili

    FlagellumFimbria Conjugation pilus

    Non-motile appendages that are chemically and

    functionally different than flagella.

    Fimbriae

    involved in adhesion

    Pili (singular = pilus)

    used in conjugation

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    C. Internal (Cytoplasmic) Structures

    Chapter Reading pp. 71-76

    Prokaryotic Ribosomes

    Ribosomes consist of 1 large and 1 small subunit.

    Carry out protein synthesis (i.e., translation of mRNA).

    both subunits are made of rRNA & ribosomal proteins

    smaller, somewhat different from eukaryotic ribosomes

    specifically targeted by some antibiotics

    Firstmembrane

    Forespore

    Vegetative cell

    Cell wall

    DNA aligns along

    the cells long axis.

    Cytoplasmic membrane

    invaginates to form

    forespore.

    Cytoplasmic membrane

    grows and engulfs

    forespore within a

    second membrane.

    Vegetative cells DNA

    disintegrates.

    DNA is replicated.1

    3

    2

    4

    Cytoplasmic

    membrane

    DNA

    Secondmembrane

    Endospores When conditions

    are bad, some

    Gram+ bacteria

    can form

    endospores:

    inactive, dormant

    cells enclosed in a

    highly resistant

    spore coat

    remain dormant until

    conditions are good

    (even 1000s of yrs!)

    very resistant to

    heating, freezing,

    dessication

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    Spore coat

    Outerspore cost

    Spore coat forms

    around endospore.

    Maturation of endospore;

    completion of spore coat

    and increase in resistance

    to heat and chemicals by

    unknown process.

    Endospore released from

    original cell.

    A cortex of calcium and

    dipicolinic acid is

    deposited between

    the membranes.

    5

    7

    6

    8

    Cortex

    Outerspore cost

    Endospore

    Completion of Endospore Formation

    The Genetic MaterialA region called the nucleoid contains the circular

    bacterial chromosome (DNA + non-histone proteins):

    usually several million

    base pairs (bp) in size

    e.g.the E. coli genome is

    ~4 mega-bps (4 Mbp)

    contains all bacterial

    genes plus an origin

    of replication (Ori)

    Ori is where DNA

    replication starts,

    essential to copy

    the chromosome

    PlasmidsSome bacteria have >1

    extrachromosomal,

    non-essential circular

    DNA molecules called

    plasmids:

    much smaller than

    bacterial chromosome

    have own Ori so it is

    copied when cell divides

    several kilo-base pairs

    (usu. 3-6 Kb)

    plasmid

    map

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    Whats the Role of Plasmids?Plasmids generally contain genes that confer

    some sort of advantage for survival and

    reproduction:

    1) genes providing protection from toxic substances

    2) genes enabling the metabolism of additional

    sources of energy

    3) genes for toxins to kill microbial competitors,

    enhance pathogenicity

    4) genes involved in gene transfer by conjugation

    including antibiotic resistance

    Inclusions & Chromatophores

    Inclusions are deposits of various materials found in

    certain types of bacteria (e.g., magnetosomes).

    Chromatophores are pigment-containing infoldings of

    the plasma membrane in some photosynthetic bacteria.

    2. Eukaryotic Cell Structure

    Chapter Reading pp. 77-86

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    Euk