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Structure and Function of Prokaryotes

Understand the biochemistry and anatomy of prokaryotic cell walls, external structures, and osmotic pressure regulation. Learn about the composition of cell walls, peptidoglycan, outer membranes, and flagella structures. Explore Gram staining, glycocalyx, and motility mechanisms in detail. Dive into the diverse functions of S-layer, capsules, and fimbriae for protection and attachment. Discover the role of cell envelope structures in maintaining osmotic equilibrium and resisting environmental stresses.

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Structure and Function of Prokaryotes

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  1. Structure and Function of Prokaryotes Structures External to the Cell Wall Cell Walls Biochemistry (Gram +/-)

  2. Prokaryote “Anatomy” Overview Cell envelope: Collectively all the structures outside from the plasma membrane.

  3. Cell Wall & Osmotic Pressure • Solutes diffuse from high to low concentration. • Net movement of water is toward higher solute concentrations. • Cells have semi-permeable membranes (water passes; solutes don’t). • Intracellular and external environment strive for isosmotic equilibrium. • Osmotic pressure, refers to that required to hold back the net movement of water. • Hypotonic environments promote “osmolysis”; unless there’s a rigid cell wall. • Hypertonic environments promote “plasmolysis”

  4. Two Cell Wall Designs:

  5. Gram StainDifferential staining to distinguish cell wall types.(Christian Gram 1884)

  6. Cell Wall BiochemistryWhat is peptidoglycan? Gram - Gram +

  7. Cell Wall BiochemistryWhat is peptidoglycan? (gly) (Inter-)

  8. Cell Wall (Gram +)

  9. Cell Wall (Gram -)(w/ Outer Membrane) Braun’s lipoprotein core (LPS = endotoxin) Periplasmic space

  10. Structures External to the Cell Wall S-layer:extremely well organized layer of protein subunits that forms a rigid mesh, or mail, next to cell wall. Functions in protection and in resisting hypoosmotic stress Glycocalyx:means sugar coating; often polysaccharide or polypeptide layer external to the cell wall. • Capsules: organized, consolidated, well attached. • Slime Layer: unorganized; loose; removed easily. • Function in attachment; protection; virulence.

  11. Structures External to the Cell Wall • Flagella: • Mostly made of flagellin. • Filament thick (20 nm) & long (10-20 µm). • Filament possibly sheathed. • Varied locations on cell: • Fimbriae: • 1000’s of thin (~5 nm) & short appendages of helical proteins. • Attachment to (specific) surfaces. • Sex Pili: • 1-10 slightly larger than fimbriae. • Only in cells with a fertility plasmid (F factor), called donors. • Attaches to like cells without F factor, called recipients. • Facilitates genetic transfer between cells; with recipient gaining the F factor and possibly other genes. peritrichous monotrichous amphitrichous lophotrichous

  12. Flagellar Motility & Chemotaxis Other kinds of motility: Spirochete; axial flagella Gliding motility; no flagella

  13. Random (searching) Positive Chemotaxis (“follow that smell”) Low [nutrient solute] High [nutrient solute]

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