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Ultrastructure of bacterial cell. Form and Function.

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Ultrastructure of bacterial cell. Form and Function. Structure of a Prokaryotic Cell Bacterial Morphology and Ultrastructure Only two types of cells are produced by ... – PowerPoint PPT presentation

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Title: Ultrastructure of bacterial cell. Form and Function.


1
Ultrastructure of bacterial cell. Form and
Function.
2
Structure of a Prokaryotic Cell
3
Bacterial Morphology and Ultrastructure
  • Only two types of cells are produced by all
    living organisms on earth.
  • Prokaryotes (pro. or primitive nucleus) do not
    have a membrane bound nucleus
  • eubacteria (true bacteria)
  • archaebacteria (ancient bacteria)
  • Eukaryotes (eu, or true nucleus) have a membrane
    bound nucleus
  • Algae
  • fungi 
  • protozoa
  • plants
  • animals

4
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5
Prokaryotes
6
Chemical Composition of Bacteria
  • Water - 70
  • Dry weight - 30 composed of
  • DNA - 5 MW 2,000,000,000
  • RNA - 12
  • protein- 70 found in
  • Ribosomes(10,000) RNA
  • Protein particles - MW 3,000,000
  • Enzymes
  • Surface structures
  • polysaccharides - 5
  • lipids - 6
  • phospholipids - 4

7
Prokaryote Structures
  1. Appendages- flagella, pili, fimbrae
  2. Cell envelope- glycocalyx, cell wall , cell
    membrane
  3. Cytoplasm- ribosomes, granules,
    nucleoid/chromosome.

8
Appendages
9
Bacterial Appendages
  • Pili (pl), pilus (s)
  • only found in gram negative bacteria
  • tubulare, hairlike structures of protein larger
    and more rare than fimbriae.
  • 2 types of pili
  • atacnement pilus - allow bacteria to attach to
    other cells
  • sex pilus, - transfer from one bacterial cell to
    another- conjugation.

10
Fimbriae
  • fimbriae (pl) fimbria (s)
  • Adhesion to cells and surfaces
  • Responsible for biofilms.
  • Pathogenesis of gonococcus and E.coli

Escherichia coli.
11
Flagella
  • Flagella (pl), flagellum(s)
  • long appendages which rotate by means of a
    "motor" located just under the cytoplasmic
    membrane.
  • bacteria may have one, a few, or many flagella in
    different positions on the cell.
  • Advantages
  • - chemotaxis - positive and negative.
  • - motility
  • All spirilla, half of bacilli, rare cocci.

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Structure of flagellaallows for 360 degree
filament rotation
14
Flagella
  • Three morphological regions
  • Helical filament
  • long outermost region composes up to 90 of its
    length
  • contains the globular (roughly spherical) protein
    flagellin arranged in several chains and form a
    helix around a hollow core
  • Hooked or curved area
  • filament is attached consists of a different
    protein
  • Basal body
  • terminal portion of the flagellum 
  • fix the flagellum to the cell wall and plasma
    membrane
  • composed of a central rod inserted into a series
    of rings
  •  
  • Gram negative - 2 pairs of rings
  • Outer pair - fixed to the outer membrane and
    peptidoglycan layer
  • Inner pair - fixed to the plasma membrane (SM
    ring)
  • Gram positive - only inner pair is present

15
Motility
  • Types of bacterial motility
  • run or swim - when a bacterium moves in
    one direction for a length of time
  • tumbles - periodic, abrupt random changes
    in direction
  • swarming - rapid wavelike growth across a
    solid culture medium
  • Mechanism of flagellar movement - relative
    rotation of the rings in the basal body of the
    flagellum
  • Antigenicity
  • flagellar or H antigen - useful in the
    serological identification of serotypes of
    Salmonella organisms

16
Arrangements
  • Flagella vary in number and arrangement.
  • Polar arrangment
  • Monotrichious - 1 flagellum at one end
  • Fastest Pseudomonas -example
  • Lophotrichious - tuft at one end
  • Amphitrichious- bipolar
  • Peritrichious - multiple flagella randomly
    dispersed around the bacterial cell
  • E. coli - example

17
Flagellar arrangements
  • Monotrichous
  • Lophotrichous
  • Amphitrichous
  • Peritrichous
  • Atrichous 

18
Axial filaments
19
Axial filaments
  • tuft of fibrils that arise at the ends of the
    cell under the outer membrane and spiral around
    the cell
  • rotation an opposing of the outer membrane
    movement that propels the spirochetes by causing
    them to move like corkscrews
  • Found in Spirochetes and are similar to flagella,
    but are located between the cell wall and an
    outer membrane, and are attached to one end of
    the organism.

20
Evidence of motility
  • Two ways by which motility can be demonstrated
  • direct or microscopic
  • hanging drop preparation or wet mount preparation
    by dark field mycroscope
  • Distinguishes
  • Brownian movement - when the bacteria show
    molecular movement
  • true motility - if a bacterium describes a
    rotatory, undulatory or sinuous movement
  • indirect or macroscopic
  • Stab inoculation of the semisolid media
  • nonmotile - growth is limited at the point of
    inoculation
  • motile - growth is diffuse or moves away from the
    line of inoculation turbidity of the medium

21
Detection of Motility
  • Direct
  • Indirect

Presence mobile bacteria
22
  • Bacterial motility (QuickTime movie)
  • http//diverge.hunter.cuny.edu/weigang/Animations
    /SalmonellaFlagella-S.mov

23
Prokaryote Structures
  • Appendages- flagella, pili, fimbrae
  • Cell envelope
  • glycocalyx
  • cell wall
  • cell membrane
  • Cytoplasm- ribosomes, granules,
    nucleoid/chromosome.

24
2. Bacterial Surface Structure - cell envelope
  • Glycocalyx - some extracellular material
    secreted by many bacterial cells in the form of
  • capsule - attached tightly to the bacterium and
    has definite boundaries.
  • slime layer - loosely associated with the
    bacterium and can be easily washed off
  • Compositions
  • layer of polysaccharide
  • proteins - sometimes

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Functions of the Capsule
  • Protection
  • Identification
  • Vaccine preparation
  • Tissue attachment
  • Antibiotic barrier
  •  

27
Medical Importance -
  • rapid serological identification of
  • Several groups of streptococci
  • Meningococcus
  • Hemophilus influenzae
  • Klebsiella pneumoniae
  • Some of the coliforms
  • Yersinia and Bacillus specie
  •  

28
Identification
  • Two simple methods to distinguish the capsule
  • India ink technique - most satisfactory method of
    demonstrating the capsule by Burri-Gins technique
  • Bacteria is suspended in diluted India ink
  • Stain with fuxin
  • Bacterial cells appear to lie in a lacunae
  • and red cytoplasme.
  •  
  • Quellung reaction - Homologous antibody is added
    to a preparation of capsule.
  • microprecipitation at the periphery of the
    capsule altering its refractive index rendering
    the capsule to be visible

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Staining by Burri-Gins
31
Neisseria meningitidis - Gram- negative coccus,
non-motile bacteria occur as two cells (orange)
in a capsule (yellow)
32
Haemophilus influenza bacteria in the process of
expressing polysaccharide capsules.
33
Cell wall
  • Peptidoglycan (polysaccharides protein),
  • Support and shape of a bacterial cell.
  • The three primary shapes in bacteria are
  • coccus (spherical),
  • bacillus (rod-shaped)
  • spirillum (spiral).
  • Mycoplasma are bacteria that have no cell wall
    and therefore have no definite shape.

34
Cell wall
  • peptidoglycan (polysaccharides protein)
  • Components of the peptidoglycan layer
  • Repeating glycan chains (N acetyl glucosamine
    and N acetyl muramic acid)
  • a set of identical tetrapeptide side chains
    attached to N- acetylmuramic acid
  • a set of identical peptide cross bridges

35
Peptidoglycan
36
Differences in Cell Wall Structure
  • Basis of Gram Stain Reaction
  • Hans Christian Gram- 1884
  • Differential Stain
  • Gram Positive vs Gram Negative Cells
  • Gram Positive Cells-
  • Thick peptidoglycan layer with embedded
    teichoic acids
  • Gram Negative Cells-
  • Thin peptidoglycan layer, outer membrane of
    lipopolysaccharide.

37
Cell wall
38
Gram Stain Reaction
  • Hans Christian Gram- 1880s
  • Divides bacteria into 2 main groups-
  • Gram positive
  • Gram negative
  • Also- gram variable
  • Gram nonreactive
  • Gram positive bacteria
  • many layers of peptidoglycan and teichoic acids.
  • form a crystal violet-iodine-teichoic acid
    complex
  • Large complex, difficult to decolorize

39
Gram positive bacteria
40
Gram Stain Reaction
  • Gram negative bacteria
  • Very thin peptidoglycan
  • No teichoic acids
  • Alcohol readily removes the crystal violet.
  • Alcohol also dissolves the lipopolysaccharide of
    the cell wall.
  • Gram variable cells
  • Some cells retain crystal violet some decolorize
    and take up the safranin
  • 4 factors-
  • Genetics- variable amount of teichoic acid.
  • Age of culture- older cultures have variable
    amount of teichoic acid
  • Growth medium- necessary nutrients not available
  • Technique-
  • smear not thin or evenly made.
  • Staining procedure not done correctly-
    decolorizer left on too long.

41
Gram negative bacteria
42

43
Gram stain technique
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45
Gram stain
46
Gram stain
47
  • Gram nonreactive cells
  • Have peptidoglycan but have very waxy- thick
    lipids waterproof, dyes cannot enter either.
  • Examples- Mycobacterium tuberculosis and leprosy.
  • Alternative staining- acid fast stain

48
Cell wall deficient forms
  • L- forms ( Lister Institute where discovered)
  • Bacteria loses cell wall during the life cycle
  • Result of a mutation in cell wall forming genes
  • Induced by treating with lysozyme or penicillin
    which disrupts the cell wall
  • Protoplast-
  • G bacterium with no c. wall, only a c.
    membrane
  • Fragile, easily lysed
  • Spheroplast-
  • G bacterium loses peptidoglycan, but has outer
    membrane
  • Less fragile but weakened.

49
Surface structures continued
  • Outer membrane
  • This lipid bilayer is found in Gram negative
    bacteria and is the source of lipopolysaccharide
    (LPS) in these bacteria
  • LPS is toxic and turns on the immune system.
  • Not found in Gram positive bacteria.

50
Lipopolysaccharide
51
C. Cell membrane
  • Located just under cell wall
  • Very thin
  • Lipid bilayer, similar to the plasma membrane of
    other cells. Transport of ions, nutrients and
    waste across the membrane
  • Typical
  • 30-40 phospholipids
  • 60-70 proteins
  • Exceptions-
  • Mycoplasma- sterols
  • Archaea- unique branched hydrocarbons

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Mesosome
  • Extension of cell membrane
  • Folding into cytoplasm internal pouch
  • Increases surface area.
  • Gram-positive bacteria-prominent
  • Gram negative bacteria- smaller, harder to see.
  • Functions-
  • Cell wall synthesis
  • Guides duplicated
    chromosomes into
    the daughter cells

    in cell division.

55
Functions of Cell Membrane
  • Carries out functions normally carried out by
    eukaryote organelles.
  • Site for energy functions
  • Nutrient processing
  • Synthesis
  • Transport of nutrients and waste
  • Selectively permeable
  • Most enzymes of respiration and ATP synthesis
  • Enzyme synthesis of structural macromolecules
  • Cell envelope and appendages
  • Secretion of toxins and enzymes into environment.

56
Prokaryote Structures
  • Appendages- flagella, pili, fimbrae
  • Cell envelope
  • glycocalyx
  • cell wall
  • cell membrane
  • Cytoplasm
  • Nucleoid/chromosome
  • Plasmid
  • Ribosomes
  • Granules

57
3. Cell cytoplasm
  • Encased by cell membrane
  • Dense, gelatinous
  • Prominent site for biochemical and synthetic
    activities
  • 70-80 water- solvent
  • Mixture of nutrients- sugar, amino acids, salts
  • Building blacks for cell synthesis and energy

58
A. Bacterial chromosome
  • Singular circular strand of DNA
  • Aggregated in a dense area- nucleiod
  • Long molecule of DNA tightly coiled around
    protein molecules.

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B. Plasmids
  • Nonessential pieces of DNA
  • Often confer protection- resistance to drugs
  • Tiny, circular
  • Free or integrated
  • Duplicate and are passed on to offspring
  • Used in genetic engineering

61
Types of plasmid
  • Fertility-F-plasmids. They are capable of
    conjugation (transfer of genetic material between
    bacteria which are touching).
  • Resistance-(R)plasmids, which contain genes that
    can build a resistance against antibiotics or
    poisons and help bacteria produce pili.
  • Col-plasmids, which contain genes that determine
    the production of bacteriocins, proteins that can
    kill other bacteria.
  • Degradative plasmids, which enable the digestion
    of unusual substances, e.g., toluene or salicylic
    acid.
  • Virulence plasmids, which turn the bacterium into
    a pathogen (one that causes disease).

62
Cell division in Prokaryotes
  • Prokaryotes use a relatively simple form of cell
    division - binary fission.
  • The diagram at 1.shows a bacterial cell.
  • The cell wall and membrane are in red,
  • the bacterial chromosome in blue,
  • the cytoplasm in light green,
  • the yellow dot represents a point of attachment
    of the chromosome to the cell membrane.

63
C. Ribosomes
  • Site of protein synthesis
  • Thousands
  • Occurs in chains polysomes
  • 70S
  • 2 smaller subunits
  • 30S and 50S

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D. Inclusions
  • If nutrients abundant- stored intracellularly
  • Granules
  • Crystals of inorganic compounds not enclosed by
    membranes
  • Polyphosphate- corynebacterium
  • Sulfur granules- photosynthetic
  • Metachromatic- Mycobacterium

66
Bacterial Internal Structures
  • Endospores
  • inert, resting, cells produced by some G genera
    Clostridium, Bacillus and Sporosarcina
  • have a 2-phase life cycle
  • vegetative cell metabolically active and
    growing
  • endospore when exposed to adverse environmental
    conditions capable of high resistance and very
    long-term survival
  • Features of spores- size, shape,
    locationidentification
  • sporulation -formation of endospores
  • hardiest of all life forms
  • Forms inside a cell- functions in survival
  • not a means of reproduction
  • withstands extremes in heat, drying, freezing,
    radiation and chemicals
  • germination- return to vegetative growth

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Endospores
  • Resistance linked to high levels of calcium and
    dipicolinic acid
  • Dehydrated, metabolically inactive thick coat
  • Longevity verges on immortality - 25,250 million
    years.
  • Resistant to ordinary cleaning methods and
    boiling
  • Pressurized steam at 120oC for 20-30 minutes will
    destroy

69
Bacterial Shapes, Arrangements, and Sizes
  • Variety in shape, size, and arrangement but
    typically described by one of three basic shapes
  • coccus - spherical
  • bacillus rod
  • coccobacillus very short and plump
  • vibrio gently curved
  • spirillum - helical, comma, twisted rod,
  • spirochete spring-like

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