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BACTERIA & ARCHAEA

CAMPBELL & REECE CHAPTER 27. BACTERIA & ARCHAEA. PROKARYOTIC ADAPTATIONS. typical prokaryote: 0.5 -5 microns unicellular variety of shapes cocci (spherical) bacilli (rods) spirochetes (corkscrews). Cell-Surface Structures. nearly all have cell wall maintains shape protects cell

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BACTERIA & ARCHAEA

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  1. CAMPBELL & REECE CHAPTER 27 BACTERIA & ARCHAEA

  2. PROKARYOTIC ADAPTATIONS • typical prokaryote: • 0.5 -5 microns • unicellular • variety of shapes • cocci (spherical) • bacilli (rods) • spirochetes (corkscrews)

  3. Cell-Surface Structures • nearly all have cell wall • maintains shape • protects cell • plasmolyze in hypertonic solution • water loss inhibits cell division hence salt used as food preservative (ham)

  4. Cell Wall Structure Prokaryotes Eukaryotes cell walls mostly cellulose or chitin ARCHAEA (-) peptidoglycan (+) variety polysaccharides & proteins • bacterial cell walls contain peptidoglycan: a polymer made of sugars cross-linked with short polypeptides

  5. Peptidoglycan

  6. Gram Staining • used to classify many bacteria as gram + or gram – • + or – staining due to differences in cell wall composition

  7. Gram + Gram - more complex less peptidoglycan + outer membrane with lipopolysaccharides • simpler cell walls • more peptidoglycan

  8. Gram + Gram -

  9. Gram + Rods Gram - Rods

  10. Medical Implications of Gram Stain Gram + Gram - many strains virulent: tends to be: toxic (fever, shock more likely) drug resistance • some strains virulent • some drug resistance (staph)

  11. Penicillin • works by inhibiting peptidoglycan cross-linking  makes cell nonfunctional • since none in eukaryotic cells  does not harm them

  12. Penicillin • Which infection would more likely respond to treatment with pcn?

  13. Prokaryotic Capsules • dense, well-defined outermost layer (called slime layer if not well-defined) • Sticky • stick to each other in a colony or to infected individual’s cells • make it more difficult for immune system to get to bacterial cell

  14. Capsules

  15. Fimbriae • used to stick to host cells • shorter & more numerous than pili

  16. Pili • appendages that pull cells together prior to DNA transfer between cells • aka sex pili

  17. Bacteria Motility • taxis: a directed movement toward or away from a stimulus • chemotaxis: movement toward a chemical (+ chemotaxis) or away from a toxic chemical (- chemotaxis)

  18. Flagella • most common structure used for prokaryotic motility

  19. Flagella • not covered by extension of plasma membrane as in eukaryotic cell flagellum • smaller (~ 1/10th width of eukaryotic flagella) • Bacteria & Archaea flagella similar in size & rotation mechanism but composed of different proteins

  20. Flagella • all these differences suggest flagella arose independently in all 3 Domains • so are analogous structures not homologous structures

  21. Flagella Archaea Bacteria

  22. Bacterial Flagella • 3 main parts: • motor • hook • filament

  23. Bacterial Flagella • evidence indicates it started as a simpler structure that has been modified in steps over time • (like evolution of eye) each step would have had to have been useful • analysis shows only ~1/2 proteins in flagellum necessary for it to function

  24. Bacterial Flagella • analysis shows only ~1/2 proteins in flagellum necessary for it to function • 19 of 21 proteins in flagella are modified versions of proteins that perform other tasks in bacteria • this is example of exaption: process in which existing structures take on new functions through descent with modification

  25. DNA in Prokaryotic Cells • most have less DNA than eukaryotic cell • circular chromosome with many fewer proteins • loop located in nucleoid • most also have a plasmid: smaller ring(s) of independently replicating DNA

  26. DNA in Prokaryotic Cells

  27. Inner Membranes in Prokaryotic Cells • So how do some prokaryotic cells undergo photosynthesis and cellular respiration if they do not have membrane-bound organelles?

  28. Inner Membranes in Prokaryotic Cells

  29. Reproduction of Prokaryotic Cells • BINARY FISSION

  30. Bacterial Reproduction • many bacteria can divide in 1- 3 hrs. (some in 20 min) • factors that slow down reproduction: • loss of nutrients • toxic metabolic waste • competition with other bacteria • eaten by predators

  31. Survivors in Extreme Environments • Halobacterium • rod-shaped • Archaea • lives in 4M saline (or higher)

  32. Endospores • developed by certain bacteria to withstand harsh conditions • resistant cells develop when essential nutrients lacking

  33. Endospores • survive boiling water • remain dormant & viable for centuries

  34. Prokaryotic Evolution • short generations (up to 20,000 in 8 yrs) • adapt rapidly • populations have high genetic diversity • have been around for 3.5 billion yrs

  35. Genetic Diversity • Factors that promote genetic diversity: • rapid reproduction • mutation • genetic recombination

  36. Rapid Reproduction & Mutation • because generations are so short even 1 mutation will produce many offspring and so increase genetic diversity which contributes to evolution

  37. Genetic Recombination • the combining of DNA from 2 sources • occurs 3 ways in prokaryotes • transformation • transduction • conjugation

  38. Transformation in Prokaryotic Cells • uptake of foreign DNA from its surroundings • many bacteria have cell-surface proteins that recognize DNA from closely related species & transport it into the cell

  39. Transformation in Prokaryotic Cells

  40. Transduction in Prokaryotic Cells • bacteriophages (phages) carry prokaryotic genes from 1 host cell to another…..usually as result of “accidents” during replicative cycle

  41. Transduction

  42. Conjugation & Plasmids • DNA is transferred between 2 prokaryotic cells (usually same species) that are temporarily joined by a mating bridge (from pilus) • transfer in 1 direction only • must have particular piece of DNA: F factor • DNA transferred either plasmid or section of loop DNA

  43. Conjugation

  44. Conjugation

  45. Plasmids & Antibiotic Resistance

  46. Genetic Recombination in Prokaryotic Cells

  47. Metabolic Adaptations in Prokaryotic Cells • phototrophs: obtain energy from light • chemotrophs: obtain energy from chemicals • autotrophs: need CO2 as carbon source • heterotrophs: require at least 1 organic nutrient to make other organic compounds

  48. Oxygen • obligate aerobes: must use O2 for cellular respiration • obligate anaerobes: O2 is toxic to them (fermentation) • faculative anaerobes: use O2 when available but also carry out fermentation if have to

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