Cell Envelope—Outer Covering 3 Basic layers: Glycocalyx, Cell wall and Cell membrane

Glycocalyx Develops a coating of macromolecules to protect cell and sometimes help it stick to its environment Slime layer, loose, helps cell retain nutrients and water Capsules are tighter and made of polysaccharides, proteins—gives a mucoid character to the colony Encapsulated bacteria have greater pathogenicity because the capsule protects the bacteria from phagocytes (WBC) that would engulf and destroy it Some glycocalyces are so adherent they are responsible for persistent colonization of non- living materials: plastic catheters, IUD’s, metal pacemakers Read pg 194, “Biofilms—The Glue of Life”—outline and hand in for reading comp/editing assignment

Cell Wall Found below the glycocalyx, determines shape of bacterium Gives structural support due to the macromolecule, peptidoglycan: Made of long sugar chains (glycan- blue & green) criss-crossed with short peptide (protein-red lines) fragments A, G, L & A—tetrapeptide chains In aqueous bacteria the cell wall prevents the absorption of too much water—cause the cell to burst Some antibiotics attack the peptide cross-links weakening the peptidoglycan, allowing cell to undergo lysis and die Some disinfectants (alcohol/detergents) will do the same Lysozyme, enzyme in saliva and tears, also breaks down cell walls

Differences in cell walls 1844—Hans Christian Gram discovered a staining technique that distinguished between 2 major groups of bacteria Difference was in their cell envelopes Gram positive cell: cell wall is a thick layer of peptidoglycan and then there is the cell membrane This thick layer absorbs the primary stain (crystal violet-purple) Then Gram’s iodine is added and it stabilizes the crystal violet to form large crystals in the peptidoglycan layer When the ETOH is added, it doesn’t wash out the purple color When the counterstain is added (safranin) its color (red) is NOT absorbed

Gram negative cells Contains 3 layers: Outer membrane (OM) acts as a sieve to only allow small molecules in; made of porin proteins—defense against antibiotics Thin peptidoglycan layer has a small periplasmic space on both sides of it— reaction site for substances entering/leaving cell Inner cell membrane Gram stain: crystal violet stains the cell purple Gram’s iodine has no affect—due to small peptidoglycan layer ETOH partially dissolves the OM’s lipids and the purple color is lost Safranin (counterstain) now stains the colorless cell The extra layer in Gram- cells makes them more impervious to some antimicrobial chemicals—except alcohol based ones

Cell Membrane Below the peptidoglycan layer Phospholipid bilayer with proteins embedded in it, EXCEPT: Mycoplasmas—membranes contain high amounts of sterols— rigid lipids that reinforce the membrane, AND… Archaea—contain unique branched hydrocarbons instead of fatty acids Can form internal folds w/in the cytoplasm called mesosomes— increases the internal surface area available for membrane activities: Regulates transport of nutrients in and wastes out Respiration and ATP synthesis occurs here (no mitochondria) Secretion of metabolic products in cell’s environment