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Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The sugar component consists of alternating residues of β-(1,4) linked ''N''-acetylglucosamine and ''N''-acetylmuramic acid. Attached to the ''N''-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer.〔(Animation of Synthesis of Peptidoglycan Layer )〕 Some Archaea have a similar layer of pseudopeptidoglycan or pseudomurein, where the sugar residues are β-(1,3) linked ''N''-acetylglucosamine and ''N''-acetyltalosaminuronic acid. That is why the cell wall of Archaea is insensitive to lysozyme.〔Madigan, M. T., J. M. Martinko, P. V. Dunlap, and D. P. Clark. Brock biology of microorganisms. 12th ed. San Francisco, CA: Pearson/Benjamin Cummings, 2009.〕 Peptidoglycan serves a structural role in the bacterial cell wall, giving structural strength, as well as counteracting the osmotic pressure of the cytoplasm. A common misconception is that peptidoglycan gives the cell its shape; however, whereas peptidoglycan helps maintain the structural strength of the cell, it is actually the MreB protein that facilitates cell shape. Peptidoglycan is also involved in binary fission during bacterial cell reproduction. The peptidoglycan layer is substantially thicker in Gram-positive bacteria (20 to 80 nanometers) than in Gram-negative bacteria (7 to 8 nanometers), with the attachment of the S-layer. Peptidoglycan forms around 90% of the dry weight of Gram-positive bacteria but only 10% of Gram-negative strains. Thus, presence of high levels of peptidoglycan is the primary determinant of the characterisation of bacteria as Gram-positive.〔C.Michael Hogan. 2010. (''Bacteria''. Encyclopedia of Earth. eds. Sidney Draggan and C.J.Cleveland, National Council for Science and the Environment, Washington DC )〕 In Gram-positive strains, it is important in attachment roles and serotyping purposes. For both Gram-positive and Gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan. == Structure == The peptidoglycan layer in the bacterial cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely ''N''-acetylglucosamine (GlcNAc or NAG) and ''N''-acetylmuramic acid (MurNAc or NAM). The alternating sugars are connected by a β-(1,4)-glycosidic bond. Each MurNAc is attached to a short (4- to 5-residue) amino acid chain, containing L-alanine, D-glutamic acid, ''meso''-diaminopimelic acid, and D-alanine in the case of ''Escherichia coli'' (a Gram-negative bacterium) or L-alanine, D-glutamine, L-lysine, and D-alanine with a 5-glycine interbridge between tetrapeptides in the case of ''Staphylococcus aureus'' (a Gram-positive bacterium). Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme DD-transpeptidase and results in a 3-dimensional structure that is strong and rigid. The specific amino acid sequence and molecular structure vary with the bacterial species. Image:Mureine.svg|The structure of peptidoglycan. Image:Gram-positive cellwall-schematic.png|Gram-positive cell wall Image:PBP catalysis.svg|Penicillin binding protein forming cross-links in newly formed bacterial cell wall. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「peptidoglycan」の詳細全文を読む スポンサード リンク
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