Peptidoglycan layer

For more information, log on to-http://shomusbiology.weebly.com/Download the study materials here-http://shomusbiology.weebly.com/bio-materials.htmlThis video describes the structure of peptidoglycan layer and the importance of their presence onto the surface of microorganisms.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 bacteria (but not Archaea), 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.[1] 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.[2] 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[citation needed].[3][4] 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.[5] In Gram-positive strains, it is important in attachment roles and stereotyping purposes.[6] For both Gram-positive and Gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan.[7]ContentsThe 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 bacteria) 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 bacteria). These amino acids, except the L-amino acids, do not occur in proteins and are thought to help protect against attacks by most peptidases[citation needed].Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme 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.[8] Source of the article published in description is Wikipedia. I am sharing their material. © by original content developers of Wikipedia.Link- http://en.wikipedia.org/wiki/Main_Page Biochemistry, 4th EditionDonald Voet, Judith G. VoetNovember 2010, ©2011