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Bacterial Cell Membranes
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Phospholipid Structure Overview
o Head = glycerol with phosphate group
 Polar, hydrophilic
o Tail = fatty acids
 Nonpolar, hydrophobic
o Forms an asymmetrical bilayer
 Fluid mosaic model
 Selectively permeable
 Receptors respond to environment
o Contains proteins
 Peripheral, integral, and transmembrane

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Bacteria and Cell Membranes
o Similar in structure to eukaryotic membranes
o 3 main functions
 Respiration
 Photosynthesis
 Lipid and cell wall synthesis

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Cell Membranes and Transportation
o Active transport = uses energy; moves molecules against gradient
 Proton motive force
 Flagellar motility
 Antibiotic pumps
 Group Transport
 Alter molecules so they won’t leak out
o Virulence
 Secretes toxins
 Porins and porin loss in antibiotic resistant bacteria

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Other Layers
o Glycocalyx = general term for secretions
 Network of polysaccharides
 Gel-like, sticky
o Slime Layer = unorganized layer of carbs
 Easily removed
o Capsule = gel layer of polysaccharides constantly produced by bacteria
 Attached; not easily removed
 Negative stains
 Source of virulence
 Hides surface antigens -> sugars are poorly detected by WBCs

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Flagella
o Eukaryotes
 Moves side to side
 Microtubules
o Prokaryotes
 Moves like propeller
 Motor proteins
o Staining
 Mordant on flagella
 Carbolfuchsin (pink) simple stain OR fluorescent antibodies

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Structure of Flagella (Bacteria)
o Filament
 Hollow, rigid, cylindrical
 Composed of flagellin
 Some have sheaths
o Hook
 Connects filament -> cell
o Basal Body
 Anchors flagella -> cell wall
 rings power the motor

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Movement of Flagella (Bacteria)
o Runs
 Counterclockwise rotation
 Forward motion
o Tumbles
 Clockwise rotation
 Disrupts run

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Chemotaxis
o Taxis = movement toward or away from stimulus
 Lower frequency of tumbles
 Directed by chemoreceptors on cell surface
o Biased Random Walk

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Spirochetes
o Mobile via axial filaments
 Endoflagella
 Anchored at one end of cell
 The whole cell moves when it rotates, causing a corkscrew motion

Bacterial Motility

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Sliminess -> Inhibits phagocytosis by macrophages

Fimbriae and Pili
o Similar in structure to flagella, but shorter and thinner
o Fimbriae
 Helps with attachment
 No motion
o Pili
 Transfer of DNA from cell to cell
 Twitching and gliding motion

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Bacterial Cell Walls
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Prokaryotes and Cell Walls
o Outside plasma membrane
o Provides shape and protects cell from osmotic breakdown
o Exceptions: mycoplasma and certain archaea

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Bacteria and Cell Walls
o Peptidoglycan makes the wall rigid
 Only bacteria have peptidoglycan
o Peptidoglycan structure
 Glycan chains of disaccharides held together by tetrapeptide chains
 Two sugars: NAG and NAM
 Layers of spirals
 Covalent bonds with peptide chains
o Peptidoglycan Crosslinks
 Contains D-isomers of amino acids and diaminopimelic acid (DAP)
 Direct connection or peptide interbridges
 site of action of Penicillin!
 attacks peptidoglycan crosslinks to weaken the cell wall
 kills bacteria

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Acid-Fast Bacteria
o Atypical cell walls
 Structure resembles Gram-positive bacteria but does not stain consistently
 Waxy lipid outer layer
 Contains mycolic acids
 Long chain of fatty acids covalently bonded to peptidoglycan
 Hydrophobic
o Actinomycetes
 Mycobacteria, diphtheriae, nocardia
o Difficult to kill
 Repels antibiotics, enzymes, and oxidizing chemicals

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Acid-Fast Stain
o Step 1: Primary Dye
 Carbofuchsin (pink)
 Uses heat to stain (steam bath)
 No mordant
Acid Fast Bacteria
Non-Acid-Fast Bacteria
o Step 2: Decolorizer
 Acid alcohol
 Removes stain from non-acid-fast bacteria
Acid Fast Bacteria
Non-Acid-Fast Bacteria
o Step 3: Counterstain
 Methylene blue
 Stains non-acid-fast bacteria
Acid Fast Bacteria
Non-Acid-Fast Bacteria

Staining
o Staining = coloring key structures of a microbe using a dye
o Smear = thin film containing a solution of microbes fixed and attached to a slide
 Fixing the microbes usually kills them ☹
Staining Basics
o Simple Stain
 Uses one basic stain, so the cells are all the same color
 Increased contrast between cells and background
o Steps for a Simple Stain
 Smear -> air dry -> fixing (using heat) -> stain -> rinse -> dry -> examine
o Basic Dyes
 Positive charge
 Bonds to negatively charged parts of the cell
o Acidic Dyes
 Negative charge
 Bonds to positively charged parts of the cell
o Mordant
 Maintains the integrity of the stain
 Enlarges specimen
Shapes and Arrangements of Bacteria
o Shape #1: Cocci (Coccus)
 Can be singular, pairs, chains, tetrads, and clusters
 Spherical
 Example: Streptococcus (chain of spherical-shaped bacteria)
o Shape #2: Bacilli (Bacillus)
 Rod-shaped
 Can also be coccoid shaped
 Curved rods = vibrios
 Singular or short chains
 Example: Bacillus anthracis
o Shape #3: Spirilla (Spirillum)
 Spiral-shaped (like a corkscrew pasta noodle 😊)
 Flexible helix = spirochete
 Example: Heliobacter pylori
o Arrangements
 One plane of division = pairs and chains
 Pairs = diplo (e
...
diplococci)
 Chains = stepto (e
...
streptococci)
 Two-three planes of division = tetrads and cubical packets
 Random planes of division = clusters
 Clusters = staphylo (e
...
staphylococcus)

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Gram Positive vs Negative Cell Walls
o Positive
 Inner plasma membrane
 Thick peptidoglycan
 Around 30 sheets!
 Permeable
 Teichoic acids
 Sugars attached to phosphate groups
 Covalently attached to peptidoglycan via NAM
 Gives peptidoglycan a negative charge
 Triggers inflammation
o Negative
 Outer and inner plasma membrane
 Outer membrane contains lipids, lipoproteins, and LPS
 Thin peptidoglycan
 Lipopolysaccharides (LPS)
 Consists of O side chain (protection from host immune system),
core polysaccharide (sugars that make cell surface negative), and
Lipid A (embedded in membrane; acts as endotoxin)
o Gram Staining
 Difference occurs during decolorizer phase

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Overview
o Nucleoid region, ribosomes, macromolecules, cytoplasm
o No membrane enclosed organelles!

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Ribosomes
o Consists of RNA and proteins
o Site of protein synthesis
o Small than eukaryotic ribosomes
 Prokaryotic: 70S, Eukaryotic: 80S
 Important because this is how scientists make drugs that specifically target
prokaryotes and leave our eukaryotic cells alone!
 Composed of 30s and 50s subunits
o Target of antibiotics
 Example: streptomycin

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Nucleoid Region
o Most bacteria only have 1 chromosome
 Closed, circular, double-stranded DNA
 Coiled and looped
 Contains nucleoid proteins
o Composed of DNA, RNA, and proteins

Cellular Structures in Bacteria

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Plasmids
o Small, circular, nonessential pieces of DNA
o Genes on plasmids carry advantages
 Example: drug resistance
o Separate from the chromosome
o Allows exchange of genetic info between different cells
o Applications in biotech
 Example: cloning

Thick peptidoglycan of gram-positive bacteria prevents crystal violet dye
from leaking out
Alcohol/alcohol acetone creates holes in the outer membrane of gramnegative bacteria, causing crystal violet dye to leak out

Staining

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Gram Stain
o Differential stain
o Gram positive bacteria stains purple
 Bacillus, Streptococcus, Staphylococcus, Mycobacterium
o Gram negative bacteria stains pink/red
 Escherichia, Heliobacter, Pseudomonas, Salmonella
o Differences in color is a result of differences in the structure of the cell walls
Gram Stain Process
o Step 1: Primary Stain
 Crystal violet
 Stains both positive and negative bacteria
Gram Positive Bacteria
Gram Negative Bacteria
o Step 2: Mordant
 Gram’s Iodine
 Forms large crystals of dye
Gram Positive Bacteria
Gram Negative Bacteria
o Step 3: Decolorizer
 Alcohol/alcohol acetone
 Removes crystal violet from Gram negative bacteria
Gram Positive Bacteria
Gram Negative Bacteria
o Step 4: Counterstain
 Safranin (red)
 Stains Gram negative bacteria
Gram Positive Bacteria
Gram Negative Bacteria



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