Download Gram Positive Cell Walls

4-b The Bacteria
pps. 77 – 106
• Bacterial cell wall
• Plasma membrane
• Structures internal to plasma membrane
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http://www.microbelibrary.org/
Search: Keen
The Gram Stain: An Animated Approach
MicrobeLibrary Visual: Animation
12/16/2005 by Daniel Cavanaugh, Mark Keen
This animation demonstrates at a molecular level the interaction of
the Gram's stain reagents in a step-by-step process with both the
gram-negative and gram-positive cell envelope.
http://www.microbelibrary.org/Gram%20Stain/details.asp?id=2020&Lang=
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Pili
Fimbriae
Flagellum
Glycocalyx
DNA
Ribosomes
Granules
(inclusions)
Cell
membrane
Plasmid
Cell wall
Cytoplasm
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The Cell Wall
• Semi-rigid structure made
of peptidoglycan
• Internal to the capsule
• External to the plasma
membrane
Capsule
Cell wall
Plasma
membrane
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Functions
• Maintain cell shape
• Protect bacteria against osmotic lysis
– Rupture of the cell resulting from movement of
water into the cell
• In some species, contributes to virulence
• Chemical composition differentiates bacteria
• Site of antibiotic damage
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Animal cells lack cell walls
Makes cell walls a good target for antibiotics
– By attacking the integrity of the cell wall
– Preventing peptidoglycan formation, cross-linking
– Example: penicillins, cephalosporins
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Peptidoglycan ‘network’
Repeated units of sugars and short
chains of amino acids
Sugars are:
– N-acetylglucosamine (NAG)
– N-acetylmuramic acid (NAM)
– Run in ‘parallel’ throughout the cell wall
– NAM links to peptide chains
– Holds the whole porous ‘mesh’ together
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Sugars
Peptides
Fig 4.13a
Small black arrows: penicillin action on peptides
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Gram Positive Cell Walls
• Thick (~ 90%) layer of peptidoglycan (20-80 nm)
• Many ‘rows’ of cross-linked peptidoglycan
stacked in ‘sheets’
• Teichoic acids, lipoteichoic acid, proteins
• The cell (plasma) membrane underneath the
cell wall
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Teichoic Acid Functions
• May regulate movement in/out of cell
• Role in growth, prevent breakdown, cell lysis
• Provide antigenic specificity
– Making it possible to identify bacteria
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Gram Negative Cell Walls
• Thin layer of peptidoglycan (~ 2 nm)
– Only one to a few ‘rows’ / ‘sheets’
• Contains more protein than Gram +
• No teichoic acids
• Contains an outer membrane
– A lipid bilayer membrane ‘outside’ the cell wall
but connected to it
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Outer Membrane Functions
•
•
•
•
Contains channels called porins = transport
Contains lipopolysaccharide (LPS)
LPS consists of polysaccharide and Lipid A
Lipid A known as endotoxin, cause fever,
shock
• O-polysaccharides
– Function as antigens, cause various diseases
– Useful to distinguish Gram negative bacteria
– Example: E. coli O157:H7 (serovar)
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Gram Stain: Differential stain…
used as an initial step to identify bacteria
Step
Gram Positive
Gram Negative
Crystal violet
Dye enters cytoplasm
Dye enters cytoplasm
Iodine
Forms crystal with CV, too
large to escape cell wall
Forms crystal with CV, too
large to escape cell wall
Alcohol
Dehydrates peptidoglycan,
impermeable to CV-I
Dissolves outer membrane,
makes holes in thin
peptidoglycan, CV-I can diffuse
out of cell
Color after alcohol
Purple
Colorless
Safranin
Purple (pink is masked by
the purple dye)
Pink
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Cell Membrane
The plasma membrane is inside the cell
wall and encloses the cytoplasm
• Phospholipid bilayer, Fluid Mosaic Model
– Similar to eukaryotes 50:50 protein to lipid
• Proteins include
– Peripheral, integral proteins
– Transmembrane proteins (active & passive
transport)
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Review Membrane Proteins
Fig 4.14a
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Cell Membrane Functions
– Production of cell wall components
– DNA replication
– Cell respiration (ATP generation via ETS)
– Act as selective or semi-permeable barrier
• Control movement of substances into & out
of cells
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Cell Membrane Destruction
Antimicrobial agents damage the cell
membrane
Alcohols
Quaternary ammonium compounds
Used as disinfectants
Antibiotics disrupt the membrane integrity
Example: polymyxins
Causes leakage of cell contents
Use for Gram negative bacteria, e.g., Pseudomonas
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Cytoplasm
Refers to all the contents w/in cell membrane
– Water (~80%)
– Proteins, enzymes
– Inorganic and organic molecules
– Nuclear area (nucleoid) containing
DNA
– Ribosomes
– Inclusions (granules)
– Plasmids
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Nuclear area (nucleoid)
nucleus-like
• Nuclear area is where the DNA is located
– Single circular molecule of double stranded
DNA
• The nucleoid is NOT a membrane-enclosed
region
Fig 4.6a
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Ribosomes
• Found in the cytoplasm not the nucleoid
area
• Organelles responsible for synthesizing
proteins
• Consist of protein and rRNA
– Smaller than ribosomes in eukaryotic cells
• 70S (50S & 30S subunits)
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Antibiotic Inhibition
• Bind to either the 30S or 50S subunits
• Cause faulty protein synthesis
> 30S:
– Streptomycin
– Gentamicin
– Tetracyclines
Fig 4.19
> 50S:
– Erythromycin
– Chloramphenicol
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Plasmids
•
•
•
•
•
Circular extrachromosomal DNA
Double-stranded DNA
Replicates autonomously
Easily passed from bacterium to bacterium
Plasmid genes are not necessary for the
survival of the bacterium
• Carry genes coding for AB resistance
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Antibiotic Resistance
• Carry genes coding for AB resistance
– Called resistance factors (R factor, p 246)
– Readily shared with other bacterial cells
– Spread AB resistance
• Have significant medical importance
• Examples:
Streptomycin, Chloramphenicol, Tetracycline
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Inclusions
Reserve deposits in the cells
Fig 4.20
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Inclusions
Purpose/Function
Polysaccharide granules
Energy reserves
Lipid inclusions
Energy reserves
Sulfur granules
Metachromatic granules
(volutin)
Energy reserves
Phosphate reserves
Carboxysomes
Ribulose 1,5-diphosphate
carboxylase, CO2 fixation
Gas vacuoles
Regulate buoyancy
Magnetosomes
Iron oxide
(destroys H2O2)
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Endospores
Dormant ‘alternate’ life forms
Bacillus
Clostridium
Obligate aerobes Obligate anaerobes
Live in soil
Normal flora: animal GI tract
• Under conditions of starvation (carbon, nitrogen)
– A spore forms w/in some of the bacteria
• Process called:Sporulation
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2.
1.
3.
4.
Sporulation
10.
5.
9.
6.
8.
See Fig. 4.21
7.
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Structure
The completed endospore consists of
– Multiple layers of resistant coats
• Cortex, spore coat, sometimes an exosporium
– Nucleoid
– Some ribosomes
– RNA molecules
– Enzymes
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Functions
Not a reproductive structure
It is a resistant, dormant survival form
– Resistant to high temperatures
– Most AB’s, disinfectants
– Low energy radiation
– Drying, etc.
• Can survive > thousands of years
• Until environmental stimuli trigger
– Germination
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Diseases
Harmless until they germinate
But, are involved in transmission of some
diseases to humans
Anthrax: Bacillus anthracis
Tetanus: Clostridium tetani
Botulism: Clostridium botulinum
Gas gangrene: Clostridium perfringens
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Bacillus anthracis
Clostridium tetani
Clostridium botulinum
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Endospore Case Study
• Botulism caused by C. botulinum = normal
flora of GI grazing animals
• Home-canned beans
– Boiled, placed in jar, lids screwed on
– The lids ‘popped’ indicating a vacuum formed
– Upon eating beans, person contracted
botulism
– Explain?
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• Endospores of C. botulinum survive in soil
– C. botulinum is an obligate anaerobe
• Endospores contaminating beans are
– Resistant to boiling and survive
– Once vacuum is formed, environment is
anaerobic
– Spores are able to germinate
– Vegetative cells replicate, secrete exotoxin
• Cause botulism
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Q’s
1. Which is NOT found in the cell walls of gramnegative bacteria?
A. Techoic acids
B. Peptidoglycan
C. Porins
D. Lipopolysaccharides
E. Outer membrane
2. Which is an incorrect pairing?
A.
B.
C.
D.
E.
Metachromatic granules : polyphosphate
Carboxysomes : carbon dioxide fixation
Lipid inclusions : b-hydroxybutyrate
Plasmids : nucleotide reserves
Magnetosomes : iron oxide
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Q’s
1.
2.
3.
4.
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Q’s
1. __________ are the primary determinants of
membrane structure, while ____________ carry
out membrane function.
2. Name three infections transmitted to
humans by bacterial endospores.
a. __________
b. __________ c. __________
3. The following bacterial structures increase
the likelihood that bacteria will be
associated with disease: capsules, fimbriae,
flagella, LPS.
True
False
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Appendix
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Name the cell type:_________ 1.
6.
2.
3.
7.
4.
5.
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Name the cell type:_________ 1.
2.
3.
4.
6.
5.
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Q’s
Match Structures
to their Functions
‗
‗
‗
‗
‗
‗
‗
‗
Structures
1. Cell wall
2. Endospore
3. Fimbriae
4. Flagella
5. Glycocalyx
6. Pili
7. Plasma membrane
8. Ribosomes
Functions
a. Attachment to surfaces
b. Contains transmembrane
proteins
c. Motility
d. Protection from changes in
water pressure
e. Protection from phagocytes
f. Resting
g. Protein synthesis
h. Susceptible to leakage of cell
contents by polymyxin
i. Transfer of genetic material
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Q’s
Functions
Match Structures
to their Functions
‗
‗
‗
‗
‗
‗
‗
‗
Structures
1. Inclusion
2. Volutin
3. Endospore
4. Plasmid
5. Ribosome
6. Forespore
7. Nucleoid
8. Sporulation
a. A structure consisting of chromosome,
cytoplasm and endospore membrane inside a
bacterial cell
b. The process of spore and endospore
formation; also called sporogenesis
c. Endoflagellum
d. Stored inorganic phosphate in a prokaryotic
cell
e. Material held inside a cell, often consisting of
reserve deposits
f. A resting structure formed inside some
bacteria
g. The region in a bacterial cell containing the
chromosome
h. A small circular DNA molecule that replicates
independently of the chromosome
i. The site of protein synthesis in a cell,
composed of RNA and protein
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Sporulation Steps
1.
2.
A vegetative cell about to enter endospore cycle
A spore septum forms as the cytoplasmic membrane
invaginates
3. Nucleoid becomes surrounded by membrane
4. Cytoplasmic membrane surrounds isolated nucleoid,
cytoplasm & membrane from step 3
5. The forespore is completed & other DNA molecule is
degraded
6. Thick protective layer, peptidoglycan, called the cortex, is
synthesized between inner & outer forespore membranes
7. A second impermeable proteinaceous protective layer
called the spore coat is synthesized
8. Sometimes a final layer, exosporium may be added
9. Vegetative portion of cell degrades, completed endospore
released
10. Bacterial endospore is completed
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