Lectures%209%20 %2010%20 the%20prokaryotic%20cell


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Lectures%209%20 %2010%20 the%20prokaryotic%20cell

  1. 1. Chapter 3 The Prokaryotic Cell <ul><li>Morphology </li></ul><ul><li>Cell Structure </li></ul><ul><li>Secretion Systems </li></ul><ul><li>Flagella / Pili </li></ul><ul><li>DNA and DNA transfer </li></ul><ul><ul><li>Chapter 8 </li></ul></ul><ul><li>Other </li></ul>
  2. 2. Morphology
  3. 3. Cell Groupings
  4. 4. Biofilms Biofilm: a polysaccharide-encased community of microorganisms can grow on many surfaces (catheters, surgical devices, pipes, teeth) extremely resistant to environmental insults (antibiotics, bactericidal agents)
  5. 5. Biofilm Architecture Water channels / nutrient access
  6. 6. Biofilm Life Cycle
  7. 7. Biofilms and Pathogenesis Vibrio cholerae biofilms protect against stomach acids
  8. 8. Prokaryotic Structures
  9. 9. Prokaryotic Structures
  10. 10. Cytoplasmic Membrane & Transport Systems Simple diffusion Movement of permeable molecules along a concentration gradient Facilitated diffusion Movement along a concentration gradient through a protein channel Active transport Movement against a concentration gradient requires energy expenditure Group translocation Chemical alteration of molecule circumvents the concentration gradient
  11. 11. Active Transport Major Facilitator Superfamily <ul><li>Energy from proton motive force used to: </li></ul><ul><li>Transport nutrients into the cell </li></ul><ul><li>Expel waste products, antimicrobial drugs, etc. out of the cell </li></ul>Circles = protons Diamond = other substance
  12. 12. Active Transport ABC Transporters ABC = ATP-binding cassette ATP hydrolysis = energy source 1. Binding protein scavenges nutrient 2. Transporter recognizes binding protein 3. Nutrient pumped into the cell with energy from ATP hydrolysis
  13. 13. Transport Systems Group Translocation Chemical alteration of molecule circumvents the concentration gradient Alteration = phosphorylation Phosphorylated nutrient is not equivalent to unphosphorylated nutrient Energy expenditure from phosyphorylation
  14. 14. Transport Mechanisms
  15. 15. Osmosis and the Cell Wall Simple diffusion Movement along a concentration gradient Osmosis Water flow to eliminate a concentration gradient Osmotic pressure on cytoplasmic membrane results in cell expansion Cell wall allows cell to withstand osmotic pressure
  16. 16. Gram-Positive / Gram Negative Cell Wall
  17. 17. Peptidoglycan Components <ul><li>Peptidoglycan </li></ul><ul><li>Only found in bacteria </li></ul><ul><li>Alternating series of two major subunits: </li></ul><ul><li>N-acetylmuramic acid (NAM) </li></ul><ul><li>N-acetylglucosamine (NAG) </li></ul><ul><li>NAM + NAG = glycan chain </li></ul><ul><li>Tetrapeptide chain </li></ul><ul><li>attached to NAM </li></ul><ul><li>cross-linkages allow for 3D structures </li></ul><ul><li>gram-negative: direct cross-links </li></ul><ul><li>gram-positive: peptide interbridge </li></ul>
  18. 18. Peptidoglycan Structure
  19. 19. Peptidoglycan: Drug Targets Lysozyme Enzyme found in bodily fluids Breaks the NAM/NAG bond Effective vs. Gram-positives
  20. 20. B-lactam Effect Control + Drug
  21. 21. Gram-Positive Cell Wall Thick peptidoglycan Teichoic acids negative charge
  22. 22. Gram-Negative Cell Wall Thin peptidoglycan layer Outer membrane another lipid bilayer + proteins LPS = outer leaflet of lipid layer lipoprotein linkage to peptidogylcan molecular barrier porins: channel-forming proteins specificity Periplasm area between outer membrane and cytoplasmic (inner) membrane filled with enzymes and proteins
  23. 23. Lipopolysaccharide (Endotoxin) O antigen Differences can be used to identify species or strains Lipid A Highly immunogenic
  24. 24. Bacteria That Lack a Cell Wall Mycoplasma Sterols strengthen and stabilize cytoplasmic membrane
  25. 25. Capsule and Slime Layer Capsule (glycocalyx) Gel-like layer for protection or attachment Distinct and gelatinous Slime layer Gel-like layer for protection or attachment Diffuse and irregular
  26. 26. Gram Negative Secretion Systems
  27. 27. Type III Secretion System Purpose: Inject virulence factors directly into the host cell cytoplasm
  28. 28. Flagella
  29. 29. Pili Pili Hollow, helical string of protein subunits arranged as a cylinder Function: 1. attachment (fimbrae) 2. solid media motility (twitching or gliding) 3. conjugation (F pilus or sex pilus)
  30. 30. Antigenic and Phase Variation <ul><li>Antigenic Variation </li></ul><ul><ul><li>Altered characteristics of surface proteins </li></ul></ul><ul><ul><li>Multiple genes for surface proteins </li></ul></ul><ul><ul><li>Expression locus: site of gene expression </li></ul></ul><ul><ul><ul><li>Random mechanism inserts different genes into locus </li></ul></ul></ul><ul><li>Phase Variation </li></ul><ul><ul><li>Gene expression switched on and off </li></ul></ul>
  31. 31. F Pilus and Conjugation Conjugation DNA transfer from one cell to another Transfer from F+ to F- cell
  32. 32. Plasmids
  33. 33. Plasmid-Encoded Traits
  34. 34. Plasmid Transfer: Conjugation
  35. 35. F Plasmid Integration Plasmid Insertion Sequences Allows plasmid integration at homologous sites in the bacterial chromosome Hfr High frequency of recombination
  36. 36. Formation of F’ Cell / F’ Plasmid Plasmid can excise from Hfr cell F’ plasmid F plasmid + small piece of chromosomal DNA transferred via conjugation recipients become F+
  37. 37. Generalized Transduction any host gene can be transferred common method of gene transfer
  38. 38. Mechanisms of DNA Transfer Transformation: Cells must be in a specialized (“competent”) state to receive DNA
  39. 39. Bacterial Chromosome(s) Nucleoid Irregular, gel-like mass of the chromosome(s) 10% of cell volume Supercoiled DNA allows tight packaging Genomics Utilization of information from large-scale genome sequencing Identification of virulence factors acquisition of virulence factors gene regulatory mechanisms genetic relatedness 2002: 87 bacterial genomes sequenced
  40. 40. DNA Transfer Transposable Elements Allows multiple genes to move as a unit from one location (chromosome or plasmid) to another location in the cell
  41. 41. Transposable Elements Acquisition of Antibiotic Resistance
  42. 42. Pathogenicity Islands <ul><li>Virulence-associated genes </li></ul><ul><li>Gram-negative, pathogen-specific </li></ul><ul><ul><li>Salmonella SPI-1, SPI-2; E. coli LEE (Pai3) </li></ul></ul><ul><li>Large (> 30 kB) distinct chromosomal units </li></ul><ul><li>Lower GC content than rest of chromosome </li></ul><ul><li>Unstable, flanked by insertion sequences </li></ul>
  43. 43. Bacterial Ribosomes Ribosomes protein + rRNA components S = Svedberg unit measure of sedimentation mRNA translation & protein synthesis important / conserved process Differences between prokaryotic and eukaryotic ribosomes can be exploited for antimicrobial therapeutics Prokaryotic ribosome (eukaryotic = 80S)
  44. 44. Bacterial Ribosomes: Drug Target
  45. 45. Endospores Forms in response to nutrient deprivation Allows cell survival in dormant state Resistant to: heat dessication toxic chemicals UV irradiation Mainly species of Bacillus and Clostridium
  46. 46. Endospore Formation Sporulation Occurs when little nitrogen or carbon is present Germination Brief exposure to heat or chemicals Endospore takes on water, swells Spore coat / cortex crack open Vegetative cell grows out 1 endospore = 1 vegetative cell not a means of reproduction
  47. 47. The Prokaryotic Cell Summary <ul><li>Morphology </li></ul><ul><li>Cell Structure </li></ul><ul><li>Secretion Systems </li></ul><ul><li>Flagella / Pili </li></ul><ul><li>DNA and DNA transfer </li></ul><ul><ul><li>Chapter 8 </li></ul></ul><ul><li>Other </li></ul>