Prokaryotic organisms

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Chapter 4

• Prokaryotic organisms

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Prokaryotic cell

• Includes bacteria and archaea
• Thousands of species of bacteria differ by
  morphology (shape), chemical composition,
  nutritional requirements, biochemical activities,
  and sources of energy
• Bacteria divide by binary fission (asexual
  reproduction)

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Size, shape, and arrangement

• Most bacteria range in size between 0.2
  micrometers (microns) to 2.0 microns
• The basic shapes are cocci, bacilli, and spirilla
• Cocci may occur in pairs (diplococci), in chains
  (streptococci), and in clusters (staphylococci)
• Bacilli may appear as single rods, diplobacilli,
  streptobacilli, or coccobacilli

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Other shapes

• Spiral bacteria have one or more twists
• Curved rods (comma shaped) are vibrios
• Others called spirilla are corkscrew shaped and
  move with whip-like appendages called flagella
• Spirochetes are helical and flexible and move by
  axial filaments
• Most bacteria maintain a single shape and are
  monomorphic, but some may have more than one
  shape and are pleomorphic

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Structures external to cell wall

• Glycocalyx means sugar coat, and is a sticky,
  gelatinous polymer that is outside the cell wall
• If the glycocalyx is firmly attached to cell wall
  and is organized it is called a capsule
• If the glycocalyx is unorganized and loosely
  attached it is called a slime layer
• Streptococcus pneumoniae, Haemophilus influenzae,
  Bacillus anthracis have them

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Flagella

• These are long, filamentous appendages that help
  bacteria move (motile)
• No flagella is called atrichous
• A single polar flagellum is monotrichous
• A tuft of flagella at each end is amphitrichous
• Two or more at one (or both) ends is
  lophotrichous
• Flagella all over is peritrichous

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Flagella

• The flagellum has 3 basic parts filament is the
  long, outermost region a hook attaches to the
  filament the basal body, which anchors the
  flagellum to the cell wall and plasma membrane
• The basal body is a small central rod inserted
  into a series of rings
• In gram negative bacteria, there are two pair of
  rings
• In gram positive bacteria, only the inner pair is
  present

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Motility

• Bacteria have a run and tumble movement thanks
  to flagella
• A bacterium with flagella can move quickly toward
  or away from a stimulus
• Bacteria moving toward chemical stimulus is
  positive chemotaxis
• Bacteria moving away is negative chemotaxis
• Moving in response to light is phototaxis

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Axial Filaments

• Spirochetes are unique in structure and motility
• Treponema pallidium causes syphilis, Borrelia
  burgdorferi causes Lyme disease
• Spirochetes move by axial filaments, which spiral
  around the cell and cause a corkscrew like
  movement

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Fimbriae and Pili

• Many gram negative bacteria contain shorter
  hairlike appendages called fimbriae and pili
• These are used for attachment and transfer of DNA
• Fimbriae help cell stick to surfaces (Neisseria
  gonorrhoeae)
• Pili (sex pili or conjugation pili) help cells
  transfer DNA in conjugation

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Cell Wall

• Helps maintain shape of the cell
• Keeps cell from rupturing
• Contributes to ability to cause disease
• Is the site of action of some antibiotics
• Helps tell differences in major types of bacteria

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Composition

• Contains peptidoglycan which consists of
  repeating disaccharides attached by polypeptides
  that forms a lattice
• Disaccharide portion has monosaccharides called
  N-acetyl glucosamine (NAG) and N-acetylmuramic
  acid (NAM)
• Alternating NAG and NAM are linked to form a
  backbone, and adjacent rows are linked by
  polypeptides

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Difference between gram positive and negative
cells

• Gram negative have an outer membrane
• Gram positive cells do not have an outer
  membrane, so the peptidoglycan is exposed and
  more easily destroyed by antibiotics like
  penicillin

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Gram negative vs. Gram positive

• Gram positive cell wall has thick peptidoglycan
• Gram negative has a thin layer
• Gram positive cell has teichoic acids which help
  bind and regulate movement of cations in/out of
  the cells
• Teichoic acids may also provide antigenic
  specificity which makes it easier to ID bacteria

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Gram negative cells

• Have thin layer of peptidoglycan and an outer
  membrane
• The outer membrane (OM) has lipopolysaccharide
  (LPS), lipoprotein, and phospholipid
• It has a negative charge which helps the bacteria
  avoid phagocytosis and complement (both are host
  defenses)

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Gram negative OM

• It also is a barrier to antibiotics, enzymes,
  etc.
• Has porins (proteins) which allow passage of some
  material in and out
• LPS component has an O polysaccharide portion and
  a lipid portion (lipid A)
• The O polysaccharide is an antigen and is used to
  help ID the bacteria
• The Lipid A is a toxin (endotoxin) that can cause
  fever and shock (endotoxin shock)

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Atypical cells

• Mycoplasma has no cell wall (causes walking
  pneumonia), but do have sterols to protect
  against rupture
• Acid Fast Cell Walls- Mycobacterium and Nocardia
  have mycolic acid in cell wall, which causes
  these bacteria to clump and stick together.
• Damage to cell wall by lysozyme causes either a
  spheroplast (gram negative) or a protoplast (gram
  positive)

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Cell or Plasma Membranehttp//library.thinkque
st.org/C004535/cell_membranes.html

• Encloses the cytoplasm
• Made of phospholipids (bilayer), proteins,
  glycoprotein, glycolipid
• Arrangement is phospholipid bilayer
• Heads (hydrophilic), tails (hydrophobic)
• Selective permeability
• ATP production occurs here
• http//www.enchantedlearning.com/subjects/bacteriu
  m/

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Movement across membranes

• Passive process-movement from high concentration
  to low without using ATP
• Includes simple diffusion (alka seltzer example)
• Facilitated diffusion-requires a protein
  transporter to allow movement across membrane
• Osmosis-movement of water from greater water to
  less water

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Osmosis http//www.tvdsb.on.ca/westmin/science/sbi
3a1/Cells/Osmosis.htm

• Movement produces osmotic pressure-this is the
  pressure needed to stop the flow of water across
  the membrane
• 3 types of osmotic solutions isotonic-equal
  solid no change in cell when placed in this type
  of solution
• Hypotonicless solid, cell will swell
• Hypertonicgreater solid cell will shrink

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Inside cell

• Cytoplasm is 80 water and contains proteins,
  carbohydrates, lipids, inorganic ions, and
  contains the nuclear area, ribosomes, and
  inclusions
• Nuclear area contains loop shaped DNA
• May have pieces of DNA called plasmids that carry
  genes for resistance (resistance factors or R
  factors)

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Inside cell continued

• Ribosomes-sites of protein synthesis
• Contained in eukaryotic cells too, but different
  because they are 80 S (Svedberg unit) 40 S 60
  S)
• Prokaryotic ribosomes are 70 S (30 S 50 S)
• Inclusions are extra storage areas including gas
  vacuoles, sulfur granules, land lipid inclusions
• Metachromatic granules -collectively known as
  volutin, represents a reserve of inorganic
  phosphate
• Magnetosomes-inclusions of iron oxide found in
  some gram negatives that act like magnets

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Endospores

• Form in gram positive rods when essential
  nutrients are depleted
• Endospores are highly durable and can survive
  extremes of heat, dehydration, and exposure to
  toxins and radiation
• Begin sporulation when a key nutrient becomes
  scarce http//student.ccbcmd.edu/courses/bio141/le
  cguide/unit1/prostruct/sporeform_an.html
• Endospores may remain dormant for years, and will
  eventually germinate and become a vegetative
  cell again
• http//student.ccbcmd.edu/courses/bio141/lecguide/
  unit1/prostruct/endobmmg.html

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Shapes, review

• Shapes cocci (spherical), bacilli (rods), vibrio
  (comma), spirochetes (spring), spirillum (helix)
• Arrangements Staphylo (clusters), strepto
  (chains), mono (single), diplo (pairs), tetrads
  (4), sarcina (8), palisade (side by side like a
  picket fence)
• Pleomorphism-variable shapes like Corynebacterium