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04.Bacterial Structure

Nam-l-alanine-d-glutamic acid-dap-d-alanine-d-alanine

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Unformatted text preview: NAM-L-Alanine-D-Glutamic Acid-DAP-D-Alanine-D-Alanine NAG NAM-L-Alanine-D-Glutamic Acid-DAP-D-Alanine-D-Alanine NAG Peptidoglycan in a Bacterial Cell Wall has Tetrapeptide Side Chains. But during “Construction” Peptidoglycan has Pentapeptide Side Chains. The Above Example is for E. coli , a Gram Negative Bacterium. Some Gram Positive Bacteria substitute L-Lysine for DAP. • Transpeptidation links - - The Subterminal (“next to last”) D-Alanine on the Pentapeptide Side Chain of one Peptidoglycan Chain - with - - The DAP of the Pentapeptide Side Chain of an adjacent Peptidoglycan Chain: NAG (D-Alanine) NAM-L-Alanine-D-Glutamic Acid-DAP-D-Alanine NAG | NAG D-Alanine-DAP-D-Glutamic Acid-L-Alanine-NAM (D-Alanine) NAG - Removal of the Terminal D-Alanines is Exergonic and “powers” the Transpeptidation Reaction (which occurs outside of the Cytoplasm). Think of each Terminal D-Alanine as a Battery Pack. • Transpeptidation results in a large, strong, flexible, Network-like Molecule NAM - NAG - NAM - NAG - NAM - NAG | | | 4AA -- 4AA 4AA -- 4AA 4AA -- 4AA | | | NAG - NAM - NAG- NAM - NAG - NAM Structure of Bacteria Page 3 Overall Structure of Gram Positive and Gram Negative Bacteria • Gram Positive - Thick Peptidoglycan Layers And that ʼ s it. Think of a Water Balloon inside a Shoebox. • Gram Negative - Outer Membrane This is outside of the Cell Wall - Thin Peptidoglycan Layer Possibly a single, interconnected Molecule of Peptidoglycan. - Periplasm The Area between the Outer Membrane and the Cell Membrane. Gram Positive Cell Walls • Thick Cell Wall composed mostly of Peptidoglycan - But may also contain Teichoic Acid (G= wall) • Teichoic Acids are only found in Gram Positive Bacteria • Tetrapeptide Side Chains are linked by Peptide Interbridges composed of several Amino Acids NAG - NAM - NAG | AA | AA | AA AA | | AA- aa - aa - aa - aa - aa -AA | Peptide Interbridge AA | AA | NAG - NAM - NAG Any of the four Amino Acids in the Tetrapeptide Side Chains can be present in the Peptide Interbridges. Other Amino Acids, particularly Glycine, Theronine, Serine, and Aspartic Acid, can also be present and their Presence is Species Specific. Structure of Bacteria Page 4 Gram Negative Cell Walls • Thin Cell Wall composed entirely of Peptidoglycan - Usually only 1 or 2 Layers Thick • Tetrapeptide Side Chains are directly linked NAG - NAM - NAG | AA | AA | AA AA | | AA- - -AA | Direct Link AA | AA | NAG - NAM - NAG • Outer Membrane - The Outer Membrane is much less permeable than the Cell Membrane • Porin Proteins join to form Transmembrane Channels - Porins give Gram Negative Bacteria Control over the Entry of Toxic Substances and Antibiotics - The Outer Membrane contains Lipopolysaccharides (LPS) • LPS are found only in the Outer Membrane of Gram Negative Bacteria The Immune System ʼ s almost hysterical Response to LPS gives rise to many Symptoms of Diseases caused by Gram Negative Bacteria • Periplasm (G = form around [perimeter]) - The Area between the Outer Membrane and Cell Membrane...
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NAM-L-Alanine-D-Glutamic Acid-DAP-D-Alanine-D-Alanine NAG...

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