Chapter 3: Microscopy and Cell Structure

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Chapter 3Microscopy andCell Structure
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Important Point
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Typical Bacterial Shapes
Also Pleomorphic Bacteria, which vary in their
shape (e.g., Corynebacterium).
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Typical Bacterial Arrangements
streptococci
sarcina
staphylococci
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ProkaryoticCell Structures
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Typical Prokaryotic Cell
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Cytoplasmic Membrane

• Movement across membrane for many substances is
  controlled by membrane proteins.
• Escherichia coli has gt200 membrane proteins.
• Many of these proteins are involved in transport
  across membranes.
• Others of these proteins allow a bacterium to
  sense its surrounding environments (e.g., as in
  chemotaxis).
• Movement is via
• Simple Diffusion (including osmosis)
• Facilitated Diffusion (with concentration
  gradient no energy expended)
• Active Transport (against concentration gradient
  energy expended)

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Simple Diffusion -- Osmosis
solute molecules/ions
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Cytoplasmic Membrane
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Protein-Mediated Transport
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Active Transport
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The Prokaryotic Cell Wall
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The Prokaryotic Cell Wall
In some cases recognized by host immune system.
Determines cell shape.
Prevents osmotic lysis.
Target for antibiotics.
In Bacteria, composed of Peptidoglycan.
Part of cell envelope.
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Gram-Pos vs. Gram-Neg.
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Gram-Positive Cell Envelope
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Gram-Negative Cell Envelope
endotoxin
cell wall
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Gram-Negative Cell Envelope
LPS Protection from antibiotics such as
penicillin plus against certain toxins.
Periplasm Site of preliminary nutrient
degradation.
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Lipopolysaccharide (LPS)
Carbohydrate has negative charge and provides
protection against some antibiotics some toxins
(e.g., detergents).
Lipid A Endotoxin
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Mycoplasma lack Cell Walls
Note Pleomorphic
Mycoplasma pneumoniae causes Walking Pneumonia
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Glycocalyx
Protection (e.g., Streptococcus pneumoniae from
phagocytosis)
Attachment (e.g., Streptococcus mutans causing
dental plaques)
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Capsule Staining
Capsules are more regular and gelatinous.
Slime Layers are less regular and more diffuse.
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Bacteria Flagella (plural)
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Flagellar Arrangements
Polar Flagellum
e.g., E. coli
also atrichous
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Chemotaxis
Also Phototaxis, etc.
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Pili (sing. Pillus)
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Fimbriae (a kind of pilli)
Tips are Adhesins, used to adhere, e.g., to
animal tissues
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Closed Circular Chromosome
Also Plasmids, which are smaller, circular pieces
of DNA.
Plasmids usually encode expendable functions,
e.g., antibiotic resistance.
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Ribosomes Sites of Translation
On order of 10,000 per cell!
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Endospores
Form inside of vegetative cells (hence endo).
Characteristic of many soil bacteria, e.g.,
Bacillus spp. Clostridium spp.
Highly resistant to heat, U.V., desiccation, etc.
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