11729936
Description
Flashcards by Candice Young, updated more than 1 year ago
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Created by Candice Young
over 6 years ago
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| Question | Answer |
| G- vs G+ | G(-): IM < Peptidoglycan < OM (cell envelope) --> PG thinner and one continuous layer, have an OM G(+): IM < Peptidoglycan --> PH thicker and have multiple layers |
| Gram Positive Cell Wall | Peptidoglycan surface: Teichoic acids (bind Ca++ and Mg++), lipoteichoic acids (modify shape and division), other transmembrane proteins |
| Gram Negative Cell Envelope | OM attached to PG by lipoproteins Periplasm in between OM and IM OM has porins for permeability, surface has lipo-polysccharides & proteins |
| lipopolysaccharides (LPS) | Lipid A (ENDOTOXIN): attached to OM; fatty acids linked to sugar phosphates, which bind Ca++ to exclude hydrophobic comp.s Core polysaccharide: attached to Lipid A, contains sugars and KDO O-specific polysaccharide (O-antigen): species/strain-specific; made of repeating branched hexoses; binds plant/animal host tissues; helps evade immune response |
| What does the hydrophyllic nature of LPS help the cell to do? | --> protects the cell surface from bile salts, hydrophobic antibiotics, and complement activation |
| peptidoglycan sacculus | one large molecule... determines the shape of the cell glycan chains run around circumference; peptide crosslinks connect glycan chains NOT a static structure, is constantly recycled |
| What is the PG wall useful for? | protects against lysis in hypotonic environments!! |
| disaccharide pentapeptide | a monomer of PG for each: NAG and NAM connected in glycan chain (contains L- and D-amino acids); DAP helps form peptide crosslinks |
| Mur pathway | PG monomer attached to bactoprenol in cytoplasmic membrane --> forms Lipid II complex, which is flipped by MurJ into periplasm --> transglycosylation adds monomer to growing glycan strand, bactoprenol recycled --> transpeptidation adds crosslinks between peptide chains attached to NAM molecules |
| Penicillin binding proteins (PBPs) | --> located in cytoplasmic membrane with soluble domains facing the periplasm High-MW: do transglycosylation and/or transpeptidation outside the cytoplasmic membrane (1 does BOTH, while 2 & 3 are only transpeptidases) Low-MW: peptidases; make peptide crosslinks, remove amino acids, or break peptide crosslinks in mature peptidoglycan |
| Lytic transglycosylases | break the β(1,4) linkages btwn NAG & NAM Ex: Lysozyme |
| SEDS proteins | --> shape, elongation, division, and sporulation can transglycosylate --> can substitute for PBP1 proteins RodA is the SEDS protein that functions in lateral walls; FtsW functions at division site |
| Normal transpeptidation mechanism | 1) serine on PBP forms covalent intermediate with the penultimate D-Ala, releasing the terminal D-ala 2) PBP-D-ala intermediate attacked by NH2 group of DAP on a neighboring peptide --> forms crosslink, releases PBP enzyme |
| Penicillin G | β-lactam antibiotic that mimics the D-ala-D-ala residues at the end of PG peptides --> accidentally attacked by DAP on peptide during transpeptidation --> β-lactam ring broken, irreversible intermediate formed --> PG cross links stop forming + continues to be lysed --> cells burst due to osmotic pressure |
| β-lactamases | enzymes that break the β-lactam ring of penicillin, inactivating the antibiotic |
| How do PBPs, LTGs, and SEDS proteins influence cell shape? | --> work at specific positions at specific times PBP2/RodA depletion (rodA ts): circular cell, no lateral cell walls PBP3 depletion (ftsI ts; ftsW ts): cell elongated, no septa PBP1 depletion: no shape at all |
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