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Dr. Alvin Fox

External layers of vegetative cells and spores, Lecture 27. Dr. Alvin Fox. KEY WORDS. Cell envelope Teichoic acid Cell wall Teichuronic acid Cell membrane Lipoteichoic acid Outer membrane Mycolic acid Peptidoglycan Undecaprenol (bactoprenol)

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Dr. Alvin Fox

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  1. External layers of vegetative cells and spores, Lecture 27 Dr. Alvin Fox

  2. KEY WORDS Cell envelopeTeichoic acid Cell wall Teichuronic acid Cell membrane Lipoteichoic acid Outer membrane Mycolic acid Peptidoglycan Undecaprenol (bactoprenol) Braun lipoprotein Endospore (spore) Porins Cell division Lipopolysaccharide

  3. Topics: • Structure of vegetative cell envelopes • unique cell envelope molecules • biosynthesis of cell wall constituents • Endospores (dormant cells) • Cell division

  4. Cell Envelope • Cell membrane + cell wall (+ plus outer membrane) • Cell wall • peptidoglycan • attached structures

  5. Bacterial cell envelopes Gram stain (+ or -) correlates with structure

  6. Gram positive Gram negative

  7. Peptidoglycan • single macromolecule • highly cross-linked • surrounds cell • provides rigidity

  8. Peptidoglycan • glycan backbone • muramic acid • glucosamine • peptide side chain • peptide cross-bridge (or direct peptide bond) • D- and L- amino acids • sometimes diaminopimelic acid

  9. Muramic acid, D-amino acidsdiaminopimelic acid • notsynthesized by mammals

  10. L-alanine D-glutamic acid L-lysine/Diaminopimelic acid D-alanine D-alanine PeptidoglycanExample with direct peptide bond Muramic acid Glucosamine

  11. Gram Positive Cell Envelope • Teichoic acid • polymer • ribitol phosphate or ribitol glycerol backbone • Teichuronic acid • polymer • no phosphorus • glucuronic acid

  12. Teichoic and teichuronic acids • Metal ion uptake • Direct autolytic enzymes • holes punched in cell wall • allows insertion cell wall (synthesis)

  13. Lipoteichoic acids cell membrane autolysins kept from cell wall

  14. r Gram Positive Cell Envelope Peptidoglycan-teichoic acid Lipoteichoic acid Cytoplasmic membrane Cytoplasm

  15. Gram Negative Peptidoglycan • Braun lipoprotein • binds cell wall to outer membrane

  16. Outer Membrane • lipopolysaccharide • phospholipids • Proteins • porins

  17. Lipopolysaccharide O-antigen Highly variable n • Core • Heptoses • Ketodeoxyoctonic acid • Lipid A • Glucosamine disaccharide • Beta hydroxy fatty acids

  18. Gram Negative Cell Envelope Lipopolysaccharide Porin Outer Membrane Braun lipoprotein Peptidoglycan Cytoplasm Inner (cytoplasmic) membrane

  19. r r r r r r r r r r Acid Fast Cell Envelope Mycolic acid lipids Peptidoglycan-arabinogalactan-mycolic acid Cytoplasmic membrane Cytoplasm

  20. Peptidoglycan synthesis 1 2 3 Cell Membrane Cytoplasm Cell wall undecaprenol sugar amino acid

  21. Lipopolysaccharide • synthesis similar to peptidoglycan • also on undecaprenol carrier

  22. Spore • Modified Gram positive bacteria cell • unusual cell envelope • cell membrane • outer membrane

  23. Spore • Peptidoglycan layer • cortex • between two membranes • less cross-linked • dehydrated muramic acid (lactam)

  24. Vegetative cell division Sporulation

  25. The endospore exosporium coat outer membrane Inner membrane cortex

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