Brock Biology of Microorganisms 11/e

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Chapter 4 Cell Structure/Function
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Compound Light Microscopy
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Compound Light Microscopy

• Magnification
• Resolution capacity to distinguish as separate 2
  adjacent points. Max resoultion of light
  microscope is 0.2 micrometers (2 points closer
  than 0.2 apart appear as one)
• Refractive Index measure of speed at which light
  passes through a material (staining increases the
  difference between refractive indexes of specimen
  and the mediumso contrast is increased)
• Brightfield illumination

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Some microorganisms are pigmented. Most are not.
Green algae
Purple phototrophic bacteria
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Staining

• Basic dyes (positive ion colored)
• Positive stains
• Acidic dyes (negative ion colored)
• Negative stains

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Steps in smear preparation and staining
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The Gram Stain (a differential stain)
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Gram StainPositive cocci and Negative rods
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Darkfield microscopy(specimem appears light
against a black background)(good for seeing
motility and very small or thin microbes)Phase
Contrast(enhances differences in refractive
indexes of structures, soyields increase
contrast) (good for seeing internal structures of
living cells)
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Darkfield
Phase contrast
Brightfield
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Cyanobacteria stained with fluorescent dye
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Three-Dimensional Imaging
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Differential Interference Contrast Microscopy
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Atomic Force Microscope (AFM)
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Confocal Scanning Laser Microscopy
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Electron Microscopy
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TEM Transmission Electron Microscopy
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SEM Scanning Electron Microscopy
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CELL SIZE (an upper limit is imposed by surface
to volume ratio)
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Prokaryotes and Eukaryotes compared

• Similarities
• Genetic material
• Cellular chemistry and metabolic pathways
• Some structures and functions

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Prokaryotes and Eukaryotes compared

• Differences (compartmentalization)
• Prokaryotes
• DNA NOT enclosed by membrane
• No membrane-bound organelles
• No histone proteins associated with DNA
• Complex cell walls
• Division by binary fission
• Eukaryotes
• DNA with a nucleus
• Membrane-bound organelles
• Histone proteins
• Cell walls absent or simple
• Division by mitosis

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• BASIC SHAPES
• Coccus
• Rod
• Spiral

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CELL STRUCTURES
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Cytoplasmic Membrane

• Phospholipid bilayer studded with proteins (Fluid
  Mosaic Model)
• Selectively permeable barrier
• Membrane strengthening agents
• Sterols in eukaryotes
• Hopanoids in some bacteria
• Archaea contain very different lipids than
  Eukarya and Bacteria

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Transport across membranes
Passive processes Diffusion/osmosis Facilitated
diffusion Active processes
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Cell Wall

• Peptidoglycan
• A polysaccharide which is the major component of
  cell walls in bacteria
• Archaea cell walls do not contain peptidoglycan
• Structure Polysaccharide chains (glycans)
  cross-linked by peptide chains of amino acids.
• Two subunits N-Acetylglucosamine (G) and
  N-Acetylmuramic acid (M)

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• Thick layer peptidoglycan
• Teichoic acid
• Lipoteichoic acid

Gram Positive Cell Wall
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• Outer Membrane
• LPS-lipopolysaccharide (Endotoxin)
• Porins
• Periplasm

Gram Negative Cell wall
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Genetic Material

• Nucleoid area of the cell in which the DNA is
  aggregated
• Single circular chromosome
• Haploid
• Plasmids

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Motility
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Flagella

• Filament
• Hook
• Basal Body

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Rotational movement of the flagella
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Polar (monotrichous)
Peritrichous
Polar (lophotrichous)
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Taxis

• Phototaxis
• Chemotaxis

Positive taxis Negative taxis
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Phototaxis Figure shows movement of an entire
colony of bacteria toward a light source at the
right of the photo (not shown)
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Ribosomes

• Site of protein synthesis
• Some structural differences between prokaryotic
  and eukaryotic ribosomes
• A major site of attack for antibiotics

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Surface Structures
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Fimbriae and Pili
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S-Layers
A surface layer made of protein found in many
bacteria
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Capsules and Slime Layers
Glycocalx polysaccharide-containing material
outside of the cell
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Inclusions/Storage Bodies/Granules
Function in storage of energy molecules or as a
reservoir of structural building blocks
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PHB (poly-B-hydroxybutric acid)
A carbon/energy storage polymer
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• Glycogen (energy storage)
• Metachromatic granules (inorganic phosphate
  reserves)

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Sulfur Granules
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Magnetosomes Iron-oxide crystals which allow the
bacteria to respond to a magnetic field
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Gas Vesicles
Small gas filled protein structures that function
to confer bouyancy on cells
Cyanobacteria bloom on lake surface
EM of gas vesicles
?
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Endospores

• Hardiest of all life forms
• For escape from unfavorable environmental
  conditions
• Germination return to the vegetative state
  from the spore state
• NOT reproductive (1 cell forms 1 endospore which
  return to reform 1 cell)

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Endosymbiont theory of Eukaryotic evolution

• Evidence in support of the hypothesis
• Mitochondria and chloroplasts contain their own
  DNA
• They contain their own ribosomes which are very
  similar to prokaryotes
• They divide independent of the cell and by binary
  fission
• Size, etc. etc