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 eubacteria. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid residues. 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. Some Archaea have a similar layer of pseudopeptidoglycan. 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 it's shape, however, while peptidoglycan helps maintain the structure of the cell, it is actually the MreB protein that facilitates cell shape. Peptidoglycan is also involved in binary fission during bacterial cell reproduction.^[1] A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are microscopic, unicellular organisms. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea are a major group of prokaryotes. ... Pseudomurein (also known as pseudopeptidoglycan) is a major cell wall component of some archaebacteria that chemically differs from but morphologically, functionally, and structurally resembles eubacterial peptidoglycan. ... A cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. ... Turgor (also called turgor pressure or osmotic pressure) is the pressure that can build in a space that is enclosed by a membrane that is permeable to a solvent of a solution such as water but not to the solutes of the soluton. ... It has been suggested that Cytoplast be merged into this article or section. ... MreB is a protein found in bacteria that has been identified as a homologue of actin. ... Binary fission Binary fission is the form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size, used by most prokaryotes. ...

The peptidoglycan layer is substantially thicker in Gram-positive bacteria (20 to 80 nm) than in Gram-negative bacteria (7 to 8 nm), 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. In Gram-positive strains, it is important in attachment roles and serotyping purposes.^[2] Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to gram-negative bacteria, which are not affected by the stain. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... A nanometre (American spelling: nanometer) is 1. ... Bacteria that are Gram-negative are not stained dark blue or violet by Gram staining, in contrast to Gram-positive bacteria. ... An S-layer is a part of cell envelope commonly found in gram-positive and gram-negative bacteria, as well as among Archaea. ...

Antibiotic inhibition

Some antibacterial drugs such as penicillin interfere with the production of peptidoglycan by binding to bacterial enzymes known as penicillin-binding proteins or transpeptidases^[2]. Penicillin-binding proteins form the bonds between oligopeptide crosslinks in peptidoglycan. For a bacterial cell to reproduce through binary fission, more than a million peptidoglycan subunits (NAM-NAG+oligopeptide) must be attached to existing subunits.^[3] Mutations in transpeptidases that lead to reduced interactions with an antibiotic are a significant source of emerging antibiotic resistance.^[4] For the Japanese rock band, see Penicillin (band). ... Penicillin core Penicillin binding proteins (PBPs) are a group of proteins which are characterized by their affinity for and binding of penicillin. ... The bacterial enzyme which cross links the peptidoglycan chains to form rigid cell walls. ... Binary fission Binary fission is the form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size, used by most prokaryotes. ... Antibiotic resistance is the ability of a micro-organism to withstand the effects of an antibiotic. ...

Considered the human body's "own antibiotic", lysozymes found in tears work by breaking the β-(1,4)-glycosidic bonds in peptidoglycan (see below) and thereby destroying many bacterial cells. Antibiotics such as penicillin commonly target bacterial cell wall formation (of which peptidoglycan is an important component) because animal cells do not have cell walls. Staphylococcus aureus - Antibiotics test plate. ... Lysozyme single crystal. ...

Structure

The structure of peptidoglycan

The peptidoglycan layer in the bacterial cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N-acetyl glucosamine (GlcNAc or NAG) and N-acetyl muramic 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, normally containing D-alanine, D-glutamic acid and mesodiaminopimelic acid. These three amino acids do not occur in proteins and are thought to help protect against attacks by most peptidases. Cross-linking between amino acids in different linear amino sugar chains by an enzyme known as transpeptidase result in a 3-dimensional structure that is strong and rigid. The specific amino acid sequence and molecular structure vary with the bacterial species.^[5] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Magnification of grains of sugar, showing their monoclinic hemihedral crystalline structure. ... N-acetyl-glucosamine (NAG) is a form of glucosamine, one of the building blocks of joint tissue and other connective tissues. ... N-acetyl muramic acid, or MurNAc, is identical to N-acetyl glucosamine (GlcNAc) except that it possesses an additional group (specifically, a propanoic acid molecule with a hydrogen atom on the middle carbon replaced by an oxygen atom to form an ether linkage) attached to Carbon 3, in place of... In chemistry, a glycosidic bond is a certain type of functional group that joins a carbohydrate (sugar) molecule to an alcohol, which may be another carbohydrate. ... Phenylalanine is one of the standard amino acids. ... Vulcanization is an example of cross-linking. ... Phenylalanine is one of the standard amino acids. ... The bacterial enzyme which cross links the peptidoglycan chains to form rigid cell walls. ... The hierarchy of scientific classification. ...

References

1. ^ Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms, 11th ed., Prentice Hall. ISBN 0-13-144329-1. 
2. ^ ^{a b} Salton MRJ, Kim KS (1996). Structure. In: Baron's Medical Microbiology (Barron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1. 
3. ^ Bauman, R. (2007). Microbiology with Diseases by Taxonomy. Benjamin Cummings. ISBN 0-8053-7679-8. 
4. ^ Spratt BG (1994). "Resistance to antibiotics mediated by target alterations". Science 264 (5157): 388-93. PMID 8153626. 
5. ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9. 

External links

• Diagrammatic representation of peptidoglycan structures.