Typical Prokaryotic Cell

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Typical Prokaryotic Cell
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ProkaryoticCell Structures
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Functions of Cell Membrane

• 1. Selective barrier (selectively permeable)
• 2. Secretes exoenzymes
• amylases
• lipases
• peptidases

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Functions of Cell Membrane

• 3. E.T.S. is located here
• 4. Enzymes for cell wall synthesis
• 5. If photosynthesis, enzymes are located on
  membranous structures called thylakoids
• 6. Mesosomes - invagination of cell membrane
  attached to DNA (Binary Fission)?

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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
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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
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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Cell Wall

• Main structural component - Peptidoglycan
• Peptidoglycan
• repeating dissacharide units
• polypeptides

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Gram-Pos vs. Gram-Neg
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Budowa mureiny
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Budowa mureiny
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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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Prokaryotic Cell Structure

• Glycocalyx - term to describe substances that
  surround bacterial cells
• 1. Capsule
• if substance is organized and firmly attached to
  cell wall
• 2. Slime Layer
• if substance is unorganized and loosely attached
  to cell wall

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Function of Capsule
1. Contribute to Virulence of bacteria by
preventing phagocytosis by WBCs
A. Streptococcus pneumoniae
B. Bacillus anthracis
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Functions of Capsules

• 2. Prevents drying out or dessication
• 3. Allows bacteria to adhere to various surfaces
• Streptococcus mutans - enamel on teeth to cause
  dental carries
• Klebseilla pneumoniae - attaches to respiratory
  tract

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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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Flagellar Arrangements
Polar Flagellum
e.g., E. coli
also atrichous
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Chemotaxis
Also Phototaxis, etc.
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Fimbriae (a kind of pilli)
Tips are Adhesins, used to adhere, e.g., to
animal tissues
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Motility

• Almost all Spiral bacteria are motile
• About 1/2 of Bacilli are motile
• Almost all Cocci are non-motile

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Axial Filament - found only in spirochetes
(flexible spirals)
Treponema pallidum
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Fimbriae

• Filamentous appendages that are shorter,
  straighter and more numerous that flagella
• found mostly in Gram (-) Bacteria
• used for attachment not motility

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E. coli (pathogenic)
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Nuclear area (nucleoid)

• 1 circular chromosome (ccDNA)
• attached to a mesosome
• segragation of DNA during Binary Fission

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Plasmids

• Small circular, extra-chromosomal pieces of DNA
• 5 to 100 genes
• Code for auxiliary metabolic functions
• antibiotic resistance
• penicillase
• production of toxins
• E. coli 0157H7

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Ribosomes - protein synthesis

• Prokaryotic Ribosome
• 70 S
• 50 S
• 30 S

• Eukaryotic Ribosomes
• 80 S
• 60 S
• 40 S

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Selective Toxicity

• Some antibiotics are aimed at the 70 S ribosomes
  of bacterial cells
• Streptomycin, Neomycin, Erythromycin and
  Tetracycline work by inhibiting protein synthesis
  by disrupting the 70 S ribosome

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Endospores - formed under periods of
environmental stress

• Only found in Gram () Bacteria
• Bacillus
• Bacillus cereus
• Bacillus anthracis
• Clostridium
• Clostridium tetani
• Clostridium botulinum
• Clostridium perfringens

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Endospores

• Extremely resistant to heat, cold, chemicals,
  lack of water, etc.
• Most vegetative bacterial cells are killed at
  temps. above 70 C (160 F)
• Endospores can survive boiling water for several
  hours (some for as long as 20 hours)

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Endospores

• Spores can remain viable for weeks, months, years
• Thermoactinomyces vulgaris
• spores found in Minnesota were 7,500 years old
  and still germinated

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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.