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Shapes of Some Prokaryotes (Slide 2)
Shapes: Cocci (Spherical), Bacilli (Rod-like), Vibrios (Comma-shaped), Spirilla (Spirals), or Spirochete (Cork-screw)
Cell can stick together after dividing to form pairs (Diplo), tetrads, chains (strepto), grape-like clusters (Staphylo-), filaments
Size range from 0.05 um diameter to >500um
E.Coli is a typical bacillus at 1X 3 um
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Parts of bacterial envelope of Gram Positive vs. Gram Negative bacteria (Slide 4)
Envelope contains plasma membrane (PM or CM), cell wall made of murein (type of peptidoglycan) and sometimes an S-layer
Gram (+) Positive have CM and cell
Gram (-) have CM but have thinner cell wall and another structure (OM) and the space between the 2 membranes (periplasmic space)
OM may be considered part of cell wall
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The Bacterial Plasma Membrane ( Slide 5)
Basic structure of CM is phospholipid bilayer w/fatty acids face inward and glycerol phosphates point outward toward cytoplasm or outside of cell
Hopanoids (related to cholesterol) act for fluidity buffers. Interact w/fatty acids within the membrane
- Lipid composition depend on microbe and its environment
- Fluidity determined by level of saturation of FA-at a given temperature the greater the number of double bonds (unsaturation) the more fluid the membrane
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Bacterial Cell Wall: Structure of Murein (Slide 6)
Murein: Consists of layers, each layer comprised of alternating NAG and NAM (lysozyme-sensitive linkage)
Each NAM has an attached short peptide that may be X-linked to another NAM short peptide on an adjacent layer (via transpeptidase)
Gram Positive bacteria: X-link of D-Ala is to gly interbridge, then bridge is X-linked to L-Lys. Walls have many layers (20-80nm) (10-40 layers)
Gram Negative bacteria: NO interbridges, Use DAP (Diaminopimelic Acid) linked to D-Ala and have fewer layers (2-7nm)
In Gram Positive: Crystal violet binds to CM. Ethanol hits cell wall and causes all layers to collapse. Crystal violet gets stuck in collapsed layers
Gram negative allows for ethanol to get to CM and wash out crystal violet
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Gram Positive Cell Wall Features (Slide 7)
Teichoic Acid are covalently attached to cell wall (or lipoteichoic acids attached to CM)
Teichoic acids give negative charge to cell wall, but function is unclear
All cell walls of Gram + or - microbes protect cells from swelling excessively in hypotonic environments
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Gram Negative Outer Membrane (Slide 8)
Inner leaflet of OM is continuation of CM
Lipopolysaccharide (LPS) is major component of outer leaflet of OM
LPS is comprised of lipid A, core polysaccharide and O antigen
Lipid A (Endotoxin) is responsible for septic shock associated w/ Gram (-) bacterial infections
OM much more permeable to solutes than PM due to presence of porins
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S-Layers (Slide 9)
Found in some bacteria (Gram + and -) and archaea (can sometime take place of cell walls)
Self assembling, crystalline structures of a single protein of glycoprotein
Model systems for studies of nanotechnology
Campylobacter use them to shield cells from immune system
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Capsules and Slime Layers (Slide 10)
Extracellular structures composed of Hi MW polysaccharides or polypeptide
Only found on some microbe. Used for attachment, protection from immune system or for protection against dessication
Important virulence factors
Slime layer part of gliding non-directed) motility in some species
Glycocalyx refers to region of slime found between organisms
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Archaeal Envelopes (Slide 11)
Closely related to Gram Positive (+) bacteria
Cell walls are non-murein always. Variable in structure
CMs contain branched lipids derived from isoprene, that are ether-linked to glycerol phosphate, no LPS in Gram Negative (-) Archaea
Hyperthermophiles contain C40 monolayers (stable at hi temp.) other archaea contain lipid bilayers or combinations, depending on environment
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Prokaryotic Appendages (Slide 12)
Flagella are most important. Most common form of prokaryotic directed motion. Used for chemotaxis
Pili (Fimbriae) are used mainly for adhesion. Buy may be used along w/slime production to create a type of twitching (non-directed) motility
Types and numbers of flagella and pili are used in classification
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Classification based on Flagella (Slide 13)
Monotrichous Polar Flagellation: One flagella at end of cell
Lophotrichoud Flagellation: Tuft of flagella at one end of cell
Peritrichous Flagellation: Flagella all around cell
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Structure of Flagella (Slide 14)
Semi-rigid, multi-component structures. Found in both Gram positive and negative cells.
Prokaryotic and eukaryotic flagella differ
In Prokaryotes: Flagella are anchored by rings assembled in each layer of the cell envelope (Basal Body)
Flagella are assembled from inside to outside via hollow internal tube-like structure
Filament is made of flagellin subunit (H antigens used for classification)
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How Flagellated Cells Move (Slide 15)
Each flagella is semi rigid and movement occurs by turning whole structure (propeller mechanism)
Torque is generated by movement of H+ into cell using Mot proteins
Rotations of flagella can be either clockwise (backward or tumbles) or counterclockwise (forward) and can be reversed by Fli proteins
Movement is in response to conc. of repellents or attractancts in environment (chemotaxis), pH taxis, phototaxis
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Endoflagella of spirochetes (Slide 16)
Axial filament/fibrils wraps around cell w/in periplasmic space
When flagella rotates, spirochetes move forward in corkscrew motion, allowing them to invade into tissues to cause disease
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Pili/Fimbriae (Slide 17)
Short, filamentous structures (usually gram - microbes) used for attachments to substrata or to other microbes in conugation (Sex pili)
Some involved in non-directed crawling motion called twitching motility but typically not involved in locomotion
Filaments are made of proteins called pilins
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Nucleoid (Slide 19)
Not rigid structure, area where DNA is found
Prokaryotes typically have singular chromosome but no nuclear membrane
Chromosome is condensed by proteins in special area (Nucleoid)
Transcription and translation occur simultaneously
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Plasmids (Slide 20)
Common extra-chromosomal circular DNAs that replicate autonomously in cytoplasm
Size varies from 1kn to over 1000kb
Copy number varies from 1 to >1000
Plasmids have auxillary (non-essential) functions
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Prokaryotic Ribosomes (Slide 21)
Site of translation. Prokaryotic cytoplasm is packed with ribosomes. contain 10-20X more ribosomes than eukaryotes
Prokaryotic ribosomes (70S) consist of 2 subunits, are functionally similar but structurally diff. than eukaryotic ribosomes (80S) and are differentially inhibited by antibiotics
Eukaryotic cells contain prokaryotic-type ribosomes in mitochondria and chloroplasts
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Prokaryotic Cytoskeleton (Slide 22)
ALL prokaryotes have cytoskeletal elements analogous to those found in eukaryotes
Functions: Cell division, protein localization and cell shape determination
Mbl (Similar to actin)
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Gas Vesicles (Slide 23)
Found in bacteria and archaea
totally impermeable to water, but permeable to gases
Purpose if for buoyancy ( NOT STORAGE)
Usually found in photosynthetic organisms
Vary in number from several to several hundred and vary in size
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Cell In
Membrane delineated structures with specific functions
Include: storage granules, inclusion bodies, carboxysomes, magnetosomes
Most are separated from cytoplasm by membrane
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PHA (polyhydroxyalkanoates) (Slide 25)
Commonly formed and used for storage of excess organic fuel molecules
PHB (Poly-B-hydroxybuterate) is most common PHA
Glycogen inclusions also occur
PHAs are enclosed in lipid membrane to form storage vesicles
Other types of molecules (phosphate, sulfur) are also stored in granules
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Magnetosomes (Slide 26)
-some: Refer to a membrane delineated structrue
Particles containing Fe(3)O(4) or Fe(3)S($=4). Essentially contains iron
Work as magnet and allow cells to align along earth's magnetic pole
Surrounded by invaginations of CM
Carboxysomes contain high levels of enzymes used to fix CO2 into carbohydrate
Enterosomes (intestinal) contain high levels of specific enzymes involved in special metabolic pathways in gut bacteria
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Endospores (Slide 27)
Specific structures found in few microbes. Critically important.
Location: Terminal, subterminal or central, characteristic of the species that make endospores
Endosporulation occurs when times get tough and cell cannot survive (Cell does not survive endospore formation)
Endospores resistant to dessication, heat, radiation, and chemicals and may survive for centuries
Endospores contain high levels of Calcium, dipicolinic acid, and SASPs (small, acid-soluble proteins) that bind to and protect DNA. Very low water content and are metabolically inactive.
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