Chapter 2

List of Topics

• Cell Wall

• Outer Membrane

• S-layer

• Capsule/slime

• Flagella

• Pili

Cell Wall

• Determines the shape of bacteria (along with cytoskeleton filaments)

  • Rod/bacilli

  • Sphere/cocci 

  • Spring/spirillum

• Provides the physical strength for the cell not to burst under extreme conditions

  • Osmotic pressure (important for cell division)

• Made of peptidoglycan

  • Polymer of sugars and amino acids

• Hydrophilic- contains lots of oxygens and nitrogen

  • Prevents hydrophobic substances from passing through

• Types

  • Bacteria

    • Specific type of peptidoglycan called murein (unique to only bacteria)

      • N-acetylmuramic acid and N-acetylglucosamine form murein, cross linked via a B-1,4- linkage bond

      • D and L amino acids for crosslinking

      • L amino acid is used in protein

      • Lysozyme breaks B 1,4 bonds

        • In our tears, milk, mucus

      • Penicillin binding protein- bifunctional

        • Glycosyltransferase- make sugar chains

        • Transpeptidase- peptide linkages

    • Gram positive

      • Very thick murein layer 10-20 layers of sugars

      • Teichoic acid- sugar alcohols linked by phosphodiester bonds, helps with adhesion to surfaces (only gram positive)

      • Crosslinking is between glysine and d-alanine

    • Gram negative

      • Thin murein layer- 1-3 layers of sugars

      • Cell wall is between two membranes (known as the periplasm)

      • Crosslinking between DAP and d-alanine

    • What would happen to a Gram + bacterial cell when lysozyme was added to the cell under the following conditions?

      • The cell is in a solution with an ionic strength > cellular contents (hypertonic solution)

        • The cell would shrink

      • The cell is in a solution with an ionic strength < cellular contents (hypotonic solution)

        • The cell would explode

    • Mycobacteria/ acid fast

      • Gram resistant-will not stain with gram stain

      • Thin murein layer

      • Waxes- mycolic acids- long chain aliphatic hydrocarbons

      • Hydrophobic cell wall

      • Keep out hydrophilic compounds due to their waxy exterior

      • Grow slowly

      • Pores allow for nutrient transfer

      • Difficult to treat with antibiotics

  • Archaea

    • Have peptidoglycan cell walls (pseudomurein)

    • Pseudomurein contains only L amino acids and has a different sugar

      • B- 1,3 linkage

    • Not affected by lysozymes

  • No cell wall

    • Limits the ability to live in different environments

    • Bacteria and archaea

    • Examples; mycoplasma, thermoplasma

Outer membrane

• Only present in gram negative organisms

• Forms periplasm

• Comprised of phospholipids, LPS- outer surface

  • LPS- lipid, o-antigen repeating subunits (toxic, causes immune response), sugar

    • Lipid A

      • Embedded into the membrane

      • Makes the membrane

      • Endotoxin

      • Toxic

    • Core polysaccharide

      • Conserved sugars

      • Negatively charges

      • Bind cations like Mg2+

    • O-antigens

      • Recognized by antibodies

      • Carbohydrate chain  (up to 40 sugars)

      • Negatively charged

      • Bind cations like Mg2+

      • Virulence factor- allows pathogen to survive better in the host

      • Hydrophilic interior, hydrophobic exterior

      • Porins- somewhat selective protein channel that allows compounds to diffuse in and out (must be 600-700 Daltons, and hydrophilic)

• Provides some structural support for the cell

  • Similar to the cell wall

• In Gram negative bacteria what excludes

  • Small hydrophilic compounds?

    • Cell (inner) membrane

  • Large hydrophilic compounds?

    • Outer Membrane, cell (inner) membrane

  • Hydrophobic compounds

    • Outer membrane (LPS), Cell wall

S-layer

• Outermost layer of gram negative, gram positive, and archaeal cells

• Crystalline/ordered structure

• Made from protein or glycoprotein

• Can self assemble

• Usually has holes that allows the passage of low molecular weight solutes

• Can be protective layer for cells with cell wall

  • Protects against phagocytosis, proteolysis, phage infection and desiccation

• Can aid with adhesion to surfaces

• Cells that are domesticated tend to lose their s-layer

Capsule/slime layer

• Capsule layer is attached to the cell while the slime is not (will be lost of the cell moves)

• High molecular weight polysaccharides

• Helps with survival

  • Protects against desiccation and phagocytosis

  • Adheres to surfaces

• Virulence factor

Flagella

• Can exist in multiple locations of the cell

• For swimming

• Aid with adhesion (stick to surfaces)

• Can be external or in the periplasm (spirochete)

• Molecular motor rotates bacterial flagella using proton motive force 

• Parts

  • Basal body- innermost part of the flagella, series of rings and rods going through the cellular envelope

  • Motor-rotates powered by the proton gradient/PMF

  • Filament- connects the cell to the filament, helical and hollow, last thing put together

• Made of flagellin

• Assembly: base to tip

  • The tip is self assembly of the flagella

Pilli/fimbriae

• Short numerous protein filaments (when compared to the flagella)

• Composed of pilin

  • At the end pf pilins there is adhesins which helps attach to surfaces

• Used for twitching motility on a surface