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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

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