Lecture 2

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Lecture 2

  1. 1. Lecture 2 Chapters 2 & 3<br />Prokaryotic Structure & Function<br />
  2. 2. Gram Staining<br />The Gram stain depends on the ability of bacteria to retain a purple color (based on cellular envelope).<br />Gram Negative<br />More numerous<br />Does not retain dye coloring<br />purple dye<br />alcohol<br />red dye<br />red<br />purple<br />
  3. 3. The Difference:<br />Gram negative has an outermembrane made up of an assortment of: <br /><ul><li>Lipopolysaccharides
  4. 4. Proteins</li></li></ul><li>
  5. 5.
  6. 6.
  7. 7. Cell Membrane = Inner Membrane<br />GRAM POSITIVE<br />Thick cell wall that protects the membrane from high internal turgor pressure<br />Made of peptidoglycan called murein<br />Mureindoes a lot!<br />Protector, provides rigidityand shape<br />Not the only determinant of bacteria cell shape<br />Provides hydrophilic layer<br />Murein is unique to bacteria making it a good target for antibiotics through preventing murein synthesis.<br />
  8. 8. Osmotic Pressure<br />Murein allows for the cell to survive under different osmoticpressures.<br />When lysozymes hydrolyze part of the murein layer the cell acts more sensitively:<br />Low osmotic pressure outside the cell: lyses<br />High osmotic pressure outside the cell: the cell changes shape (rod to sphere)<br />In gram negative this is called protoplasts<br />In gram positive this is called spheroplasts<br />
  9. 9. High osmotic pressure<br />Low osmotic pressure<br />Shape Change<br />Low osmotic pressure outside the cell lyse <br />High osmotic pressure outside the cell  shape change<br />
  10. 10. The Different Shapes of Bacteria<br />Plural<br />Singular Spirillum Bacillus Coccus<br />
  11. 11. Cell Membrane + Outer Membrane<br />GRAM NEGATIVE<br />Thin murein layer connected to the outer membrane by a lipoptein<br />Periplasm - space between the two membranes<br />The outer membrane contains LPS<br />LPS is unique to prokaryotes!<br />lipid A<br />Causes fever and shock<br />Core<br />O antigen<br />Immunogenic/toxic, highly variable<br />Hydrophilic polysaccharides on O antigen keep out hydrophobic compounds just like in gram positive<br />
  12. 12. LPS Structure<br />Core<br />O Antigen<br />Lipid A<br />Portion that sticks out of cell<br />Hydrophilic<br />
  13. 13. Gram Negative<br />
  14. 14. Gram Positive<br />
  15. 15. Transportation<br />GRAM NEGATIVE<br />The outer membrane contains special channels called porins that allow hydrophilic compounds such as sugars, aa’s, and ions inside the cell (nonspecific).<br />Large molecules – rely on active transport and energy usually coupled with inner membrane transport<br />
  16. 16. Capsules and slime layers<br />Found in both +/-<br />Capsule: slime attached to cells<br />Slime layer: looser layer<br />Role:<br />Enables bacteria to adhere to surfaces<br />Bacterial defense against phagocytosis<br />Prevents desiccation(dehydration) <br />
  17. 17. Flagella<br />Flagella – helical filaments that rotate and act as propellers<br />Composed of three parts: filament connected via a hook to a basal body.<br />
  18. 18. Different types of Flagella<br />
  19. 19. Filament - composed of a single protein, flagellin<br />Hook – connects filament to the cell<br />Basal Body – composed of 15 proteins that aggregate to form a rod<br />
  20. 20. Flagella – (Regulated) Process<br />Basal body assembled and inserted into cell envelope<br />Hook is added<br />Filament is assembled progressively by the addition of new flagellin subunits to its growing tip.<br />Flagella grow from the tip outward with a hollow channel where the flagellin molecules are extruded<br />A regulated process – inhibitor secreted once basal body is inserted<br />
  21. 21.
  22. 22. Pili<br />Common in gram-negative bacteria<br />Functions include:<br />Gene transfer<br />Motility <br />Adhere to mucosal surfaces<br />Inhibit phagocytic ability of white blood cells<br />
  23. 23. Motility<br />Pili are straight rods – do not rotate!<br />“Twitching Motility” – move by pulling themselves across a solid surface<br />Growth<br />Grow from the inside of the cell outward unlike flagella<br />Pili vs. Flagella<br />
  24. 24. The Cell Interior<br />Prokaryote<br />Eukaryote<br />
  25. 25. The Nucleoid<br />Contains DNA consisting of a large circular chromosome<br />With exceptions<br />No membrane <br />With exceptions, an example is: Plantctomycetes<br />
  26. 26. DNA Packaging<br />Long DNA is tightly folded into nucleoid<br />Condensing DNA requires high ion concentration and DNA binding proteins<br />Supercoilingof DNA also aids in packaging<br />
  27. 27. DNA Supercoiling<br />Supercoiled circular DNA lowers the energy barrier for strand separation<br />Balance of two enzymes:<br />DNA gyrasewhich does the supercoiling<br />Topoiseomerase I which does the uncoiling<br />
  28. 28. Genome Comparison<br />Prokaryotic Range<br />580,000 base pairs – 10 million base pairs<br />Eukaryotic Range2.9 million base pairs – 4 billion base pairs<br />
  29. 29. DNA Copies & Plasmids<br />Often multiple chromosome copies are seen in the cell because of rapid growth<br />Decreasing growth rate  single nucleoid<br />Plasmids<br /> carry extrachromosomal material<br />“Disposable”<br />
  30. 30. Cytoplasm<br />Crowded inside the cell<br />Viscous (gel-like)<br />Chemical reactions within a bacterial cell take place in an environment totally different from what is common in test tube studies<br />
  31. 31. Gas Vesicles<br />Structures filled with gas similar to that of the environment<br />Vesicles surrounded by protein shell<br />Allow buoyancy for the cell so it can set level in water column (and get the right amount of light)<br />Ultimate purpose: control buoyancy for photosynthetic bacteria<br />
  32. 32. Other Internal Structures<br />Other structures found in bacteria and archaea play roles in:<br />Photosynthesis<br />Chemoautotrophy<br />Carbon fixation<br />Gorwth on certain substrates<br />Magnetosomes (bacteria contain tiny magnets and they can orient themselves by responding to the magnetic fields on earth)<br />

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