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

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






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

    • Chapter 3 The Prokaryotic Cell
      • Morphology
      • Cell Structure
      • Secretion Systems
      • Flagella / Pili
      • DNA and DNA transfer
        • Chapter 8
      • Other
    • Morphology
    • Cell Groupings
    • 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)
    • Biofilm Architecture Water channels / nutrient access
    • Biofilm Life Cycle
    • Biofilms and Pathogenesis Vibrio cholerae biofilms protect against stomach acids
    • Prokaryotic Structures
    • Prokaryotic Structures
    • 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
    • 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
    • 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
    • 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
    • Transport Mechanisms
    • 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
    • Gram-Positive / Gram Negative Cell Wall
    • 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
    • Peptidoglycan Structure
    • Peptidoglycan: Drug Targets Lysozyme Enzyme found in bodily fluids Breaks the NAM/NAG bond Effective vs. Gram-positives
    • B-lactam Effect Control + Drug
    • Gram-Positive Cell Wall Thick peptidoglycan Teichoic acids negative charge
    • 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
    • Lipopolysaccharide (Endotoxin) O antigen Differences can be used to identify species or strains Lipid A Highly immunogenic
    • Bacteria That Lack a Cell Wall Mycoplasma Sterols strengthen and stabilize cytoplasmic membrane
    • 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
    • Gram Negative Secretion Systems
    • Type III Secretion System Purpose: Inject virulence factors directly into the host cell cytoplasm
    • Flagella
    • 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)
    • 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
    • F Pilus and Conjugation Conjugation DNA transfer from one cell to another Transfer from F+ to F- cell
    • Plasmids
    • Plasmid-Encoded Traits
    • Plasmid Transfer: Conjugation
    • F Plasmid Integration Plasmid Insertion Sequences Allows plasmid integration at homologous sites in the bacterial chromosome Hfr High frequency of recombination
    • 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+
    • Generalized Transduction any host gene can be transferred common method of gene transfer
    • Mechanisms of DNA Transfer Transformation: Cells must be in a specialized (“competent”) state to receive DNA
    • 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
    • DNA Transfer Transposable Elements Allows multiple genes to move as a unit from one location (chromosome or plasmid) to another location in the cell
    • Transposable Elements Acquisition of Antibiotic Resistance
    • 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
    • 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)
    • Bacterial Ribosomes: Drug Target
    • 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
    • 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
    • The Prokaryotic Cell Summary
      • Morphology
      • Cell Structure
      • Secretion Systems
      • Flagella / Pili
      • DNA and DNA transfer
        • Chapter 8
      • Other