Chapter 5 Micro

• Cell (plasma) membrane


  Separates the cytoplasm from the outside environment. Phospholipid bilayer with proteins
• Bacterial Membrane Protein Functions


  • Support for structures that protrude from the cell (flagella, pili)
  • Signaling and communication
  • Export of toxins and other virulence factors
  • Transport of substances in/out of the cell across the membrane
  • Establish concentration gradients for energy transfer
• Cell wall


  A single, interlinked molecule that encloses the entire cell
• Bacterial Cell Wall Types


  • Gram-positive: thick cell wall, multiple layers of peptidoglycan (Bacillus anthracis, Streptococcus pyogenes)
  • Gram-negative: thin cell wall, single layer of peptidoglycan, enclosed by an outer membrane (Escherichia coli, Pseudomonas aeruginosa)
• Gram-Negative Close-up


  • Murein lipoprotein: inner leaflet of the outer membrane that forms a peptide bond with peptidoglycan
  • Lipopolysaccharide (LPS): outer leaflet of the outer membrane; lipid A and polysaccharide chains
• Other Cell Wall Types


  • Acid-Fast Cell Wall: Complex cell wall with peptidoglycan and mycolic acid, Resistant to staining (Mycobacterium tuberculosis, Mycobacterium leprae)
  • Mollicutes: bacteria without a true cell wall (Mycoplasma, Ureaplasma)
• Bacterial DNA


  Organized in a nucleoid. Many bacteria also contain plasmids, small extrachromosomal circles of DNA that confer additional beneficial functions (eg, antibiotic resistance)
• Bacterial Cell Division


  1. DNA replication

  2. Protein synthesis and expansion of cytoplasm causes cell to elongate

  3. Septum forms and the cell divides
• Septum formation (septation) and motility


  • Determines the microscopic arrangement of cells
  • Cells form pairs (diplo-), chains (strepto-), or palisades when they septate in parallel planes (Ex. - diplococci, streptobacilli)
  • Cells form packets of 4 or 8 when they septate in alternating parallel planes (Ex. - cocci in tetrads, sarcinae)
  • Cells form clusters if they septate in random orientations (Ex. - staphylococci)
• Pili


  • Made of pilin protein
  • Fimbriae (attachment pili) attach cells to surfaces
  • Conjugation (sex) pilus facilitates transfer of DNA between cells
• Flagella


  • Enable motility and chemotaxis
  • Flagella filament is made of flagellin protein
  • Rotation of flagella propels the cell in response to stimuli
• Adaptive Structures for Diverse Environments


  • Thylakoid membranes (Photosynthetic bacteria)
  • Gas vesicles (Aquatic bacteria inflate/deflate for buoyancy)
  • Storage granules (Storage of nutrients such as sulfur, phosphate, or PHA)
  • Magnetosomes (Store magnetite (iron oxides) for magnetotaxis)