MBIO 1010 Lecture 7

• more than 200 abc transport systems known
• solute binding protein is the part that will transport something
• integral membrane proteins are the transmembrane proteins
• ATP-hydrolyzing proteins supply energy for the transport event
• Cell walls of bacteria

  • Outside the cell membrane - still associated with the cell
  • Rigid - helps determine the cell shape
  • Not a major permeability barrier
  • Porous to most small molecules - can get into
  • Protects the cell from osmotic changes
  • critical structure for viability - it being alive
  • Penicillin targets the cell wall of bacteria, if you can degrade the cell wall you can kill the bacteria
• Function of the cell wall

  • prevents cell expansion - protects against osmotic lysis
  • protects against toxic substances - large hydrophobic molecules
  • ex. detergents, antibiotics
  • pathogenicity
  • helps evade host immune system
  • help bacterium stick to surfaces
  • partly responsible for cell shape
• Isotonic solution

  • no net movement of water
  • not changing the concentration
  • concentration of solutes is the same inside and outside
• Hypotonic solution

  • water moves into the cell and may cause the cell to burst if the wall is weak or damaged (osmotic lysis)
  • low concentration outside, high concentration inside
• Hypertonic solution

  • water moves out of the cell, causing its cytoplasm to shrink (plasmolysis)
  • high concentration of solute outside, low concentration solute inside
• pathogenicity - bacteria that cause disease
• Peptidoglycan = pg
• LPS = Lipopolysaccharide
• Gram positive and gram negatives have different cell wall structure

  • gram negative cell wall
  • two layers: LPS and thin peptidoglycan
  • gram positive cell wall
  • one layer: thick peptidoglycan
• Peptidoglycan is composed of beige circles (glycan chains) alternating sugars that are connected by blue strings (peptides amino acids) linked together
• Peptidoglycan is a rigid layer that provides strength to the cell wall
• polysaccharide composed of

  • N-acetylglucosamine and N-acetylmuramic acid
  • amino acids
  • Lysine or diaminopimelic acid (DAP)
  • Cross-linked differently in gram negative bacteria and gram positive bacteria
  • form a glycan tetrapeptide
• Peptidoglycan

  • always attached to NAM
  • always alternating nam and nag
• conserve - always the same
• Depicting gram negative and gram positive from cross-links

  • gram negative: crosslinked at the third amino acid
  • gram positive: have an interbridge and at the third amino acid is connected to 5 glycine
• there are glycosidic bonds between sugars
• between sugars there is beta (1-4) linkages
• significance of that linkage is that lysozyme is able to cleafve
• gram positive cell walls

  • contains up to 90% peptidoglycan - so it is a major component of the cell wall
  • common to have teichoic acids (acidic substances) embedded in their cell wall - built from repeating units
  • lipoteichoic acids: teichoic acids covalently bound to membrane lipids