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



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  • 1. Chapter 3 The Prokaryotic Cell
    • Morphology
    • Cell Structure
    • Secretion Systems
    • Flagella / Pili
    • DNA and DNA transfer
      • Chapter 8
    • Other
  • 2. Morphology
  • 3. Cell Groupings
  • 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. Biofilm Architecture Water channels / nutrient access
  • 6. Biofilm Life Cycle
  • 7. Biofilms and Pathogenesis Vibrio cholerae biofilms protect against stomach acids
  • 8. Prokaryotic Structures
  • 9. Prokaryotic Structures
  • 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. Active Transport Major Facilitator Superfamily
    • Energy from proton motive force used to:
    • Transport nutrients into the cell
    • Expel waste products, antimicrobial drugs, etc. out of the cell
    Circles = protons Diamond = other substance
  • 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. 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. Transport Mechanisms
  • 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. Gram-Positive / Gram Negative Cell Wall
  • 17. Peptidoglycan Components
    • Peptidoglycan
    • Only found in bacteria
    • Alternating series of two major subunits:
    • N-acetylmuramic acid (NAM)
    • N-acetylglucosamine (NAG)
    • NAM + NAG = glycan chain
    • Tetrapeptide chain
    • attached to NAM
    • cross-linkages allow for 3D structures
    • gram-negative: direct cross-links
    • gram-positive: peptide interbridge
  • 18. Peptidoglycan Structure
  • 19. Peptidoglycan: Drug Targets Lysozyme Enzyme found in bodily fluids Breaks the NAM/NAG bond Effective vs. Gram-positives
  • 20. B-lactam Effect Control + Drug
  • 21. Gram-Positive Cell Wall Thick peptidoglycan Teichoic acids negative charge
  • 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. Lipopolysaccharide (Endotoxin) O antigen Differences can be used to identify species or strains Lipid A Highly immunogenic
  • 24. Bacteria That Lack a Cell Wall Mycoplasma Sterols strengthen and stabilize cytoplasmic membrane
  • 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. Gram Negative Secretion Systems
  • 27. Type III Secretion System Purpose: Inject virulence factors directly into the host cell cytoplasm
  • 28. Flagella
  • 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. Antigenic and Phase Variation
    • Antigenic Variation
      • Altered characteristics of surface proteins
      • Multiple genes for surface proteins
      • Expression locus: site of gene expression
        • Random mechanism inserts different genes into locus
    • Phase Variation
      • Gene expression switched on and off
  • 31. F Pilus and Conjugation Conjugation DNA transfer from one cell to another Transfer from F+ to F- cell
  • 32. Plasmids
  • 33. Plasmid-Encoded Traits
  • 34. Plasmid Transfer: Conjugation
  • 35. F Plasmid Integration Plasmid Insertion Sequences Allows plasmid integration at homologous sites in the bacterial chromosome Hfr High frequency of recombination
  • 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. Generalized Transduction any host gene can be transferred common method of gene transfer
  • 38. Mechanisms of DNA Transfer Transformation: Cells must be in a specialized (“competent”) state to receive DNA
  • 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. 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. Transposable Elements Acquisition of Antibiotic Resistance
  • 42. Pathogenicity Islands
    • Virulence-associated genes
    • Gram-negative, pathogen-specific
      • Salmonella SPI-1, SPI-2; E. coli LEE (Pai3)
    • Large (> 30 kB) distinct chromosomal units
    • Lower GC content than rest of chromosome
    • Unstable, flanked by insertion sequences
  • 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. Bacterial Ribosomes: Drug Target
  • 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. 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. The Prokaryotic Cell Summary
    • Morphology
    • Cell Structure
    • Secretion Systems
    • Flagella / Pili
    • DNA and DNA transfer
      • Chapter 8
    • Other