BIOL 3340

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BIOL 3340

• Chapter 3

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Chapter 3

• Microbial Cell Structure

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Types of Cells

• Two major classes eukaryotes prokaryotes.
• Differences the materials making up the nucleus
  of eukaryotic cells are separated from the rest
  of the cell by the nuclear membrane, whereas in
  prokaryotic cells these materials are not
  separated.
• All animals and plant cells are eukaryotic
  including fungi. Bacteria, cyanobacteria and the
  mycoplasmas are prokaryotic.

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Size, Shape, and Arrangement of Bacterial cells

• Cocci (s., coccus) spheres
• diplococci (s., diplococcus) pairs
• streptococci chains
• staphylococci grape-like clusters
• tetrads 4 cocci in a square
• sarcinae cubic configuration of 8 cocci

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Size, Shape, and Arrangement

• Bacilli (s., bacillus) rods
• coccobacilli very short rods
• vibrios resemble rods, comma shaped
• spirilla (s., spirillum) rigid helices
• spirochetes flexible helices
• mycelium network of long, multinucleate
  filaments Check on line lab Manual for Bacterial
  shapes)

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Size, Shape, and Arrangement

• Sizes
• Typically 0.1 - 20 ?m (with some exceptions)
• Typical coccus 1 ?m (e.g. Staphylococcus)
• Typical short rod 1 x 5 ?m (e.g. E. coli)
• Barely within the best resolution of a good
  compound light microscope

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Bacterial Shapes
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Cell Structureof Procaryotes

• Prokaryotic cells
• The constituents of a typical bacterium are as
  follows
• Bacterial Cell Wall and Capsule bacteria are
  surrounded by a cell wall, which not only
  contains polysaccharide but also contains protein
  and lipid.
• In some bacteria, the cell wall is surrounded by
  the capsule.
• The cell wall and capsule provide shape and form
  to the bacterium and also acts as a physical
  barrier between the bacterium and its
  environment.
• Nucleoids in bacteria the nuclear material is
  concentrated in a region called the nucleoid
  within the cytoplasm.

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A typical Bacterial Cell
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.Cell Structure

• There is no membrane-bound nucleus in
  prokaryotes.
• Instead the DNA is located within a specialized
  region of the cytoplasm of the cell called the
  nucleoid region.
• There is no nuclear membrane surrounding the
  nucleoid.
• Bacterial flagella many bacteria possess one or
  more flagella for locomotion.

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Gram-negative Cell Walls and Acid Fast Fast
cell wall in Chapter 3
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Procaryotic Cell Membranes

• Cell Membranes
• membranes are an absolute requirement for all
  living organisms.
• plasma membrane encompasses the cytoplasm
• some procaryotes also have internal membrane
  systems

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Functions of the Plasma Membrane

• separation of cell from its environment
• selectively permeable barrier
• some molecules are allowed to pass into or out of
  the cell
• transport systems aid in movement of molecules
• detection of and response to chemicals in
  surroundings with the aid of special receptor
  molecules in the membrane

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Fluid Mosaic Model of Membrane Structure
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..Plasma membrane
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..Plasma membrane
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Phospholipid layer

• polar ends
• interact with water
• hydrophillic
• nonpolar ends
• insoluble in water
• hydrophobic

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Membrane Proteins

• Peripheral proteins
• loosely associated with the membrane and easily
  removed
• Integral proteins
• embedded within the membrane and not easily
  removed

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Procaryotic Cytoplasm

• Cytoplamic Matrix
• Cytoplasm contains the nucleoid, ribosomes and
  inclusion bodies
• lacks organelles bound by unit membranes
• composed largely of water
• is a major part of the protoplasm (the plasma
  membrane and everything within)

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..Cytoplasmic Matrix

• Viscous aqueous suspension of proteins, nucleic
  acid, dissolved organic compounds, mineral salts
• Network of protein fibers similar to the
  eukaryotic cytoskeleton.
• Cytoplasmic Inclusion Bodies
• granules of organic or inorganic material that
  are stockpiled by the cell for future use.
• some are enclosed by a single-layered membrane

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.Cytoplasmic inclusions

• Cytoplasmic inclusions
• Glycogen Granules
• Poly-?-hydroxybutyrate granules
• Lipid droplets
• Gas vacuoles
• Metachromatic granules(Phosphate crystals or
  volutin granules)
• Sulfur Granules

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Ribosomes

• Ribosomes
• complex structures consisting of protein and RNA
• sites of protein synthesis
• smaller than eucaryotic ribosomes
• procaryotic ribosomes ? 70S
• eucaryotic ribosomes ? 80S

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The Nucleoid

• Nucleoid
• irregularly shaped region
• location of chromosome
• usually 1/cell
• not membrane-bound

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The Procaryotic Chromosome

• The Chromosomes
• usually a closed circular, double-stranded DNA
  molecule
• looped and coiled extensively

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Plasmids

• Plasmids
• usually small, closed circular DNA molecules
• exist and replicate independently of chromosome
• have relatively few genes present

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Procaryotic Cell Walls

• Prokaryotic Cell Wall
• rigid structure that lies just outside the plasma
  membrane (detail to continue)

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Functions of Cell Wall

• provides characteristic shape to cell
• protects the cell from osmotic lysis
• may also contribute to pathogenicity
• very few procaryotes lack cell walls

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Cell Walls of Bacteria

• Gram Staining developed by Gram in 1888
• bacteria are divided into two major groups based
  on the response to gram-stain procedure
• gram-positive bacteria stain purple
• gram-negative bacteria stain pink
• staining reaction due to cell wall structure

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Gram Positive and Gram negative
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Gram-Positive Cell Walls

• Gram positive bacteria composed primarily of
  peptidoglycan
• Peptidoglycan are polymers which contains
  N-acetylglucosamine and N-acetylmuramic acid and
  several different amino acids
• Walls contain teichoic acid ( polymers of
  glycerol or ribitol joined by phosphate groups)

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..Gram-Positive Cell Walls

• The periplasmic space lies between plasma
  membrane and cell wall and is smaller than that
  of gram-negative bacteria
• periplasm has relatively few proteins
• enzymes secreted by gram-positive bacteria are
  called exoenzymes

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Gram-Negative Cell Walls

• consist of a thin layer of peptidoglycan
  surrounded by an outer membrane
• outer membrane composed of lipids, lipoproteins,
  and lipopolysaccharide (LPS)
• no teichoic acids

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..Gram Negative

• more complex than gram-positive walls
• periplasmic space differs from that in
  gram-positive cells
• may constitute 20-40 of cell volume
• many enzymes present in periplasm

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Gram Positive and Negative cell Wall
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Assignments

• Features of a prokaryotic cell
• List the differences between a gram positive and
  gram negative cell wall.

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Variations on Cell Wall Architecture

• Acid-fast Cell Walls
• Many genera in the High GC gram-positive
  bacterial group contain mycolic acids, embedded
  in the peptidoglycan .
• Mycolic acids are a class of waxy, extremely
  hydrophobic lipids.
• Certain genera contain very large amounts of this
  lipid, and are difficult to gram stain.
• These genera may be identified by the acid-fast
  staining technique.
• Includes Mycobacterium and Nocardia.

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..Variations on Cell Wall Architecture

• Mycoplasmas
• Bacteria that are naturally have no cell walls
• Includes Mycoplasma and Ureaplasma
• Archaea
• Have archaea cell walls with no peptidoglycan
• Many have cell walls containing pseudomurein, a
  polysaccharide similar to peptidoglycan but
  containing N-acetylglucosamine and
  N-acetyltalosaminuronic acid .

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Capsules, Slime Layers, and S-Layers

• Layers of material lying outside the cell wall
• capsules
• usually composed of polysaccharides
• well organized and not easily removed from cell
• slime layers
• similar to capsules except diffuse, unorganized
  and easily removed.
• a capsule or slime layer composed of
  polysaccharides can also be referred to as a
  glycocalyx

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Glycocalyx
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S-layers

• S-layers
• regularly structured layers of protein or
  glycoprotein.
• in bacteria the S-layer is external to the cell
  wall.
• Regular floor tile pattern.
• Function not clear -- Stability?

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Functions of Capsules, Slime Layers, and S-layers

• protection from host defenses (e.g.,
  phagocytosis)
• protection from harsh environmental conditions
  (e.g., desiccation) , chemicals or osmotic stress
• attachment to surfaces
• facilitate motility
• nutrient Storage

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Pili and Fimbriae

• Fimbriae (s., fimbria)
• short, thin, hairlike, proteinaceous appendages
  up to 1,000/cell
• mediate attachment to surfaces
• sex pili (s., pilus)
• similar to fimbriae except longer, thicker, and
  less numerous (1-10/cell)
• required for mating

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Fimbriae
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Fimbriae

• Function s
• Mobility
• Almost all motile bacteria are motile by means of
  flagella
• Motile vs. non motile bacteria.
• Different species have different flagella
  arrangements
• Structure
• Filament composed of the protein flagellin
• Hook Rotor Assembly Permits rotational
  "spinning" movement

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Fimbriae
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Chemotaxis

• movement towards a chemical attractant or away
  from a chemical repellent
• concentrations of chemical attractants and
  chemical repellents detected by chemoreceptors on
  surfaces of cells

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Bacterial Endospores

• Bacterial Spores
• are formed by some bacteria as dormant
  structures.
• resistant to numerous environmental conditions
  e.g heat, radiation,chemicals, nutrient
  depletion,
• desiccation, and waste buildup .
• Bacterial spores are NOT a reproductive
  structure, like plant or fungal spores.
• Produced by very few genera of bacteria
• Major examples Bacillus Clostridium

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endospores
Sporogenesis
Sporogenesis
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Sporogenesis

• Sporogenesis
• Also called endospore formation or sporulation
• normally commences when growth ceases because of
  lack of nutrients
• A copy of the bacterial chromosome is surrounded
  by a thick, durable spore coat .
• When the vegetative cell dies and ruptures, the
  free spore is released.
• When spore encounters favorable growth
  conditions, spore coat ruptures and a new
  vegetative cell is formed.

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..SporogenesisComplex multistage process
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Spore Germination
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Bibliography

• http//en.wikipedia.org/wiki/Scientific_method
• https//files.kennesaw.edu/faculty/jhendrix/bio334
  0/home.html
• Lecture PowerPoints Prescotts Principles of
  Microbiology-Mc Graw Hill Co.
• http//www.bio.mtu.edu/campbell/prokaryo.htmhttp/
  /molecular-biology.suite101.com/article.cfm/cell_s
  tructure
• http//water.me.vccs.edu/courses/ENV108/lesson5_2.
  htm