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C hair of Medical Biology, M icrobiology, V irology, and I mmunology

C hair of Medical Biology, M icrobiology, V irology, and I mmunology. CELL S TRUCTURE OF BACTERIA. Lecturer As. Prof. O. Pokryshko. The Dimension of Bacteria. Relative size of a bacterial cell compared to other cells including viruses. Bacterial surface structures. Cell Envelope.

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C hair of Medical Biology, M icrobiology, V irology, and I mmunology

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  1. Chair of Medical Biology, Microbiology, Virology, and Immunology CELL STRUCTURE OF BACTERIA. Lecturer As. Prof. O. Pokryshko

  2. The Dimension of Bacteria Relative size of a bacterial cell compared to other cells including viruses.

  3. Bacterial surface structures

  4. Cell Envelope • Cytoplasmic membrane • Cell wall Cell wall-less bacteria • No peptidoglycan layer • Cell membrane contains sterols for stability Mycoplasma pneumoniae

  5. Cytoplasmic Membrane • Phospholipid bilayer • “Fluid mosaic” model • Embedded proteins for active transport • Enzymes for energy generation • Photosynthetic pigments

  6. Cell membrane Peripheral Membrane Protein Phospholipid Integral Membrane Protein Peripheral Membrane Protein

  7. Function of Cytoplasmic Membrane • Selective permeability to different molecules. • Active transport aided by permease. • Play a role in DNA replication. • Cell wall biosynthesis. • Mesosomes ----- cell division.

  8. Cell wall • Two major groups of bacteria based on structure of cell wall • Gram positive • Thick peptidoglycan layer • Gram negative • Thin peptidoglycan layer • Outer membrane containing LPS • Gram stain is crucial first step toward identification

  9. Peptidoglycan (cell wall)

  10. Cell Wall • Gram positive cell wall • Thick peptidoglycan (PG) layer • Acidic polysaccharides • Teichoic acid and lipoteichoic acid • Gram-negative cell wall • Thin peptidoglycan (PG) layer • Lipopolysaccharide layer • Porins • Periplasmic space

  11. Gram-positive cell envelope

  12. Gram-negative cell envelope

  13. Cell Wall Structures Structures associated with gram-positive and gram-negative cell walls.

  14. Function of Cell Wall • Maintenance of the shape (due to rigidity of peptidoglycan). • Protects the cytoplasmic membrane cell contents • Rigidity • Cell wall is osmotically insensitive • Hypotonic solution – cell burst. • Hypertonic solution – cell shrank. • Isotonic solution – bacteria is life.

  15. L Forms Mutations can cause some bacteria to lose the ability to synthesize the cell wall and are called L forms.

  16. Capsules • are important for • Adhesion (Associated with virulence in bacteria) • Avoidance of immune response (Protects bacteria from phagocytic cells) • Protection from dehydration

  17. Capsule Streptococcus pneumoniae Klebsiella pneumoniae Bacillus anthracis

  18. External structures • Pili (Fimbriae)play roles in • Adhesion • Exchange of genetic material • Avoidance of immune response • Flagella are important for • Motility (dispersal) • Antigenic determinant (“H” antigens)Number and location species specific

  19. Pili and flagella Fimbriae are smaller than flagella and are important for attachment. Salmonella

  20. Pili Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another (“mating”).

  21. Flagellar Structure Three components of a flagellum: filament, hook and basal body It composed of protein subunits calledflagellin.

  22. Flagellar Arrangement • Monotrichous (b) Lophotrichous • (c) Amphitrichous (d) Peritrichous

  23. Bacterial Motility The rotation of the flagella enables bacteria to be motile.

  24. Internal Structures • Cytoplasm • Genome • Inclusion bodies • Endospore

  25. Cytoplasm • Gelatinous solution containing water, nutrients, proteins, and genetic material • Site for cell metabolism

  26. Chemical Analysis of Microbial Cytoplasm 70% water Proteins 96% of cell is composed of 6 elements: carbon hydrogen oxygen phosphorous sulfur nitrogen 26

  27. Bacterial Genome Most bacteria contain a single circular double strand of DNA called a nucleoid.

  28. Prokaryotic Ribosome • A ribosome is a combination of RNA and protein, and is the site for protein synthesis • Composed of large (50S) and small (30S) subunits • S = Svedverg unit, measures molecular size

  29. Inclusion Bodies Inclusion bodies enable a cell to store nutrients and to survive in nutrient depleted environments

  30. Bacterial Spores Some bacteria, notably those of the genera Bacillus and Clostridium, develop a highly resistant resting phase or endospore that does not grow or reproduce and exhibit absolute dormancy (not detectable metabolism).

  31. Endospores Bacillus anthracis

  32. Vegatitive form • The bacteria actively growing, non spore stage of a bacterium. • Sporulation: • Formed on exposure to unfavorable condition,E.g., • Nutrient depletion • Changes • Moisture, • Temperature, • pH or • Oxygen tension • Spore requires 10-15 hours to form.

  33. Endospore formation

  34. Germination • Mature endoscope are metabolically inert • Changes in the environment • Retuning to vegetative state within 15 minutes. • In the process of germination the spores absorb water and swell, the protective coat disintegrates and a single vegatitive cell emerges.

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