peptidoglycan composition &Gram (+) vs. Gram (-) cell walls
peptidoglycan- A.A. CHOs (backbones)
1) N-acetylglucosamine (glucose deriv.) 2) N-acetylmuramic acid (unique to peptidoglycan)
peptidoglycan (murein) synthesis steps:
1) autolysins (bact. enzymes) BREAK glycosidic bonds btwn NAG-NAM & peptide cross-bridge linking the NAG-NAM rows 2) bactoprenols transport NAG-NAM-pentapeptide across the cytoplasmic membrane a) interaction w/ transglycosidases-insert monomers into existing peptidoglycan 3) transglycosidase enzymes insert & link new peptidoglycan monomers (NAG-NAM-pentapeptide) into the peptidoglycan breaks a) transpetidase enzymes reform cross-links btwn rows & layers of peptidoglycan→strong peptidoglycan wall
peptidoglycan- A.A.s (cross-links)
1) common A.A.- L-form (e.g. L-alanine, L-lysisne) 2) unique to murein- D-form (e.g. D-alanine, D-glutamic acid) 3) unique to Gram (-)- diamino pimelic acid
gram (-) cell wall chemically complex
1) minor part-[AA sugars (NAG-NAM)+AAs] 2) major part- a) phospholipids b) lipoproteins c) lipopolysaccharides (lipid=lipid A, polysaccharride= variable) d) pore-forming proteins (porins)
gram (-) cell wall component f(x)s
1) peptidoglycan prevents osmotic lysis 2) outer membrane a) channels for entry/exit of solutes via PORINS (protein pores) b) retains certain enzymes + prevents entry of some toxins (e.g. penicillin G, lysozyme) c) LPS in outer membrane adds strength to outer membrane d) fusion w/ outer mem of other gram (-) bact [communication, (obtain: virulence factors, resistance genes), toxin delivery to human cells] 3) surface proteins [enzymes, adhesions, invasions (occassionally), resisting phagocytocis (in certain bact.)] 4) periplasm contains enzymes for (nutri: break down, transfer across cytoplasmic mem)
gram (+) cell wall component f(x)s
1) peptidoglycan prevents osmotic lysis 2) teichoic acids (if present) likely strengthen cell wall 3) surface proteins can f(x) as: [enzymes, adhesions, invasions (occassionally), resisting phagocytosis (in certain bact.)] 4) periplasm contains enzymes for nutri breakdown
gram (+) or gram (-) cell wall?
Gram-negative cell wall composed of thin, inner layer of peptidoglycan and an outer membrane consisting of molecules of phospholipids, lipopolysaccharides (LPS), lipoproteins and sutface proteins. The lipopolysaccharide consists of lipid A and O polysaccharide.
gram (+) or gram (-) cell wall?
Gram-positive: cell wall appears as dense layer composition being (generally) numerous rows of peptidoglycan, and molecules of lipoteichoic acid, wall teichoic acid and surface proteins
f(x) of pore forming proteins (porins) in gram (-)
channels for entry/exit of solutes through outer membrane of cell wall
peptidoglycan monomers (NAG-NAM-pentapeptide) are synthesized in the:
cytosol of the bact. where they attach to a bactoprenol (membrane carrier molecule)
lipopolysaccharride (LPS) aka
endotoxin
significance to bacterial pathogenicity- gram (-) cell wall components
lipid A portion (endotoxin) of the LPS in outer membrane- during severe systemic infection (large # bact.present) high levels LPS released = macrophages --> excessive cytokine (can harm body)
Gram (+) cell wall structure
major or only component= thick, dense, highly cross-linked peptidoglycan layers with teichoic acids & M proteins being +/- for presence
Gram (-) cell wall structure
minor inner component= thin, less dense, weakly cross-linked peptidoglycan layers major component= complex multi-layered outer wall (membrane)
PAMPS (pathogen associated molecular patterns)/MAMPS (microbe associated molecular patterns)
molecules unique to microbes not being associated w/ human cells
S-layer structure
n S-layer (surface layer) is a part of the cell envelope commonly found in bacteria, as well as among archaea .[1] It consists of a monomolecular layer composed of identical proteins or glycoproteins.
gram (+) cell wall chemically simple
only has 1) [AA sugars (NAG-NAM) + AAs] & 2) sometimes (+/- presence) teichoic acids &/or M-proteins
antibiotics inhibit normal peptidoglycan synth. resulting in
osmotic lysis (bacteria bursts due to weak wall)
peptidoglycan (murein) general def
polymer consisting of interlocking chains of peptidoglycan monomers (NAG-NAM-pentapeptide)
significance to bacterial pathogenicity- gram (+) cell wall components
severe systemic infection (large # bact. present) high levels of PAMPs released = macrophages--> excessive cytokines (can harm body)
