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MSU MMG 301 - Lecture 4

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Lecture 41. Draw the structure of the outer membrane of Gram- bacteria and name the different components of the outer membrane 2. Compare and contrast the inner and outer leaflets of the outer membrane of Gram- bacteria a. Inner: phospholipids and proteinsb. Outer: Lipopolysaccaride (LPS), phospholipids, proteins3. Draw the general structure of the LPS, describe the overall composition of Each componenta. Lipid A: dimer of glucosamine (GlcN) with attached long-chain fatty acids inserted into the OMb. Core Polysaccharide: non-repeated, contains 6 carbon, 7 carbon, and 8 carbon sugarsc. O-specific polysaccharide (o- antigen): one oligosaccharide repeated several times. Often strain specific4. Explain the five functions of the LPS a. Major structural component of the OMi. Lipid A: essential for the formation, stabilization, and function of the OM, thus viability and growth of the cellb. Toxicity to animals: (LPS = endotoxin). Responsible for some bacterial illnesses (ex. Salmonella food infection)c. Localization of specific proteins to the OM; these proteins function in closeassociation with LPSd. Protection against entry of certain toxic extracellular substances into the cell (bile for E. coli)e. O- specific polysaccharide recognized by bacteriophages and by immune system of warm-blooded animals5. Describe the outer membrane porins and their functional properties a. Trimeric trans-membrane proteins, water filled channelsb. Non specific transport of small hydrophobic molecules by passive diffusionacross OMc. Exclude hydrophobic and large hydrophilic solutes d. Some are solute- specific (LamB for maltose)6. Explain how the structure of the Braun lipoprotein and its location allow it to accomplish its function a. Anchors OM to the peptidoglycan. Helps create the periplasmb. High affinity receptors for transport of low concentration nutrientsc. Enzymes that hydrolyze large extracellular polymers7. Name the functions of periplasmic proteins a. Nutrient-binding proteins for solute specific nutrient uptakeb. Chemoreceptor proteins involved in chemotaxisc. Catabolic scavenging enzymes, degrade complex substrates d. Enzymes for synthesis of peptidoglycan and other envelope componentse. Detoxifying enzymes (= degrade toxins), ne of many ways bacteria can resist antibiotics8. Describe the molecular structure of the peptidoglycan a. Gram Negativei. 1-3 layersii. Poorly cross-linkediii. Brauns lipoprotein link to outer membraneb. Gram Positivei. Up to 25 layersii. Highly cross linkediii. Teichoic and lipoteichoic acids links to cytoplasmic membrane9. Explain how the peptidoglycan forms a unique, continuous sheet (murein. sacculus) around the cytoplasmic membrane a. Parallel strands of repeated disaccharide (G-M), tetrapeptide linked to Mb. D- amino acids; and meso-DAP (diaminopimelic acid)c. Some covalent cross-links between adjacent tetrapeptidesd. Murein sacculus: covalently-linked sheet of peptidoglycan completely enclosing the cell10. Explain how the peptidoglycan protects cells from lysis in dilute solutionsa. Protoplast lyses when not protected by a rigid wallb. Bacterial cell wall maintains structural integrity 11. Explain what happens to Gram+ and Gram- bacteria that are treated with lysozyme in isotonic solutions a. Lysozyme digestion releases an intact protoplast (gram+) or a spheroplastwith OM remnants (Gram -)12. Compare and contrast teichoic acids and lipoteichoic acids a. Teichoic Acids (Gram +)i. Ribitol-P or glycerol-P polymers, side chains of amino acids or sugarsii. Covalently attached to peptidoglycanb. Lipoteichoic acidsi. Covalently attached to membrane lipidsii. Rigidify cell wall, regulate cell growthiii. Major surface component, recognized by the immune system of warm-blooded animalsiv. Chemistry varies in different Gram + bacteria13. Explain the functions of teichoic acids and lipoteichoic


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MSU MMG 301 - Lecture 4

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