Polysaccharides are polymeric A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties carbohydrate A carbohydrate is an organic compound with the general formula Cmn, that is, consists only of carbon, hydrogen and oxygen, with the last two in the 2:1 atom ratio. Carbohydrates can be viewed as hydrates of carbon, hence their name. Structurally however, it is more accurate to view them as polyhydroxy aldehydes and ketones structures, formed of repeating units (either mono- or di-saccharides) joined together by glycosidic bonds In chemistry, a glycosidic bond is a type of functional group that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate. These structures are often linear, but may contain various degrees of branching. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules A macromolecule is a very large molecule most often created by some form of polymerization. In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles. The constituent molecules from which macromolecules are assembled are called can have distinct properties from their monosaccharide building blocks. They may be amorphous An "amorphous solid" is a solid in which there is no long-range order of the positions of the atoms. . Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous solid, many polymers (such as polystyrene) are amorphous, and even junkfoods such as cotton candy are or even insoluble Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on temperature and pressure. The extent of the solubility of a substance in a in water.^[1][2]

When all the monosaccharides in a polysaccharide are the same type the polysaccharide is called a homopolysaccharide, but when more than one type of monosaccharide is present they are called heteropolysaccharides.

Examples include storage polysaccharides such as starch Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store. It is the most important carbohydrate in the human diet and is contained in such staple foods as potatoes, wheat, maize , rice, and cassava and glycogen Glycogen is the molecule that functions as the secondary long-term energy storage in animal and fungi cells. It is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach. Glycogen is the analogue of starch, a less branched glucose polymer in plants, and is commonly referred to as animal, and structural polysaccharides such as cellulose Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units and chitin Chitin n (pronounced /ˈkaɪtɨn/) is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. It is the main component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g. crabs, lobsters and shrimps) and insects, the radulas of mollusks and.

Polysaccharides have a general formula of C_x(H₂O)_y where x is usually a large number between 200 and 2500. Considering that the repeating units in the polymer backbone are often six-carbon monosaccharides, the general formula can also be represented as (C₆H₁₀O₅)_n where 40≤n≤3000.

Storage polysaccharides

Starches

Starches Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store. It is the most important carbohydrate in the human diet and is contained in such staple foods as potatoes, wheat, maize , rice, and cassava are glucose Glucose , a simple sugar (monosaccharide), is an important carbohydrate in biology. Cells use it as a source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and starts cellular respiration. Starch and cellulose are polymers derived from the dehydration of glucose. The name "glucose" comes polymers in which glucopyranose Glucose , a simple sugar (monosaccharide), is an important carbohydrate in biology. Cells use it as a source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and starts cellular respiration. Starch and cellulose are polymers derived from the dehydration of glucose. The name "glucose" comes units are bonded by alpha-linkages. It is made up of a mixture of Amylose This polysaccharide is one of the two components of starch, making up approximately 20-30% of the structure. The other component is amylopectin, which makes up 70-80% of the structure (15–20%) and Amylopectin Amylopectin is a polysaccharide and highly branched polymer of glucose found in plants. It is one of the two components of starch, the other being amylose (80–85%). Amylose consists of a linear chain of several hundred glucose molecules and Amylopectin is a branched molecule made of several thousand glucose units (every chain 24–30 glucose unit). Starches are insoluble Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on temperature and pressure. The extent of the solubility of a substance in a in water Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam. They can be digested by hydrolysis, catalyzed by enzymes called amylases Amylase is an enzyme that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion. Foods that contain much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns some of their starch into sugar in the mouth. The pancreas also makes, which can break the alpha-linkages (glycosidic bonds). Humans and other animals have amylases, so they can digest starches. Potato The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species. Despite being first introduced outside the Andes region four centuries ago,, rice Rice is the seed of the monocot plant Oryza sativa. As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East, South, Southeast Asia, the Middle East, Latin America, and the West Indies. It is the grain with the second highest worldwide production, after maize, wheat Wheat is a grass, originally from the Fertile Crescent region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize (784 million tons) and rice (651 million tons). Globally, wheat is the leading source of vegetable protein in human food, having a, and maize Maize is a grass domesticated by indigenous peoples in Mesoamerica in prehistoric times. The Aztecs and Mayans cultivated it in numerous varieties throughout central and southern Mexico, to cook or grind in a process called nixtamalization. Later the crop spread through much of the Americas. Between 1250 A.D. and 1700 A.D. nearly the whole are major sources of starch in the human diet. The formation of starches are the way that plants store glucose.

Glycogen

Glycogen Glycogen is the molecule that functions as the secondary long-term energy storage in animal and fungi cells. It is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach. Glycogen is the analogue of starch, a less branched glucose polymer in plants, and is commonly referred to as animal is a polysaccharide that is found in animals and is composed of a branched chain of glucose residues. It is stored in liver and muscles.

Structural polysaccharides

Cellulose

The structural component of plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004, are formed primarily from cellulose Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units. Wood is largely cellulose and lignin Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood. It is one of the most abundant organic polymers on Earth, exceeded only by cellulose,, while paper Paper is a thin material mainly used for writing upon, printing upon or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets and cotton Cotton is a soft, fluffy staple fiber that grows in a boll around the seeds of the cotton plant. The plant is a shrub native to tropical and subtropical regions around the world, including the Americas, Pakistan, India and Africa. The fiber most often is spun into yarn or thread and used to make a soft, breathable textile, which is the most widely are nearly pure cellulose. Cellulose is a polymer A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties made with repeated glucose units bonded together by beta-linkages. Humans and many other animals lack an enzyme to break the beta-linkages, so they do not digest cellulose. Certain animals can digest cellulose, because bacteria possessing the enzyme are present in their gut. The classic example is the termite The termites are a group of eusocial insects usually classified at the taxonomic rank of order Isoptera . Along with ants and some bees and wasps which are all placed in the separate order Hymenoptera, termites divide labour among gender lines, produce overlapping generations and take care of young collectively. Termites mostly feed on dead plant.

Chitin

Chitin Chitin n (pronounced /ˈkaɪtɨn/) is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. It is the main component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g. crabs, lobsters and shrimps) and insects, the radulas of mollusks and is one of many naturally occurring polymers A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties. It is one of the most abundant natural materials in the world. Over time it is bio-degradable in the natural environment. Its breakdown may be catalyzed by enzymes Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their called chitinases Chitinases are digestive enzymes that break down glycosidic bonds in chitin. Because chitin composes the cell walls of fungi and exoskeletal elements of some animals , chitinases are generally found in organisms that either need to reshape their own chitin or to dissolve and digest the chitin of fungi or animals, secreted by microorganisms such as bacteria The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, and fungi A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. The Fungi (pronounced /ˈfʌndʒaɪ/ or /ˈfʌŋɡaɪ/) are classified as a kingdom that is separate from plants, animals and bacteria. One major difference is that fungal cells have cell, and produced by some plants. Some of these microorganisms have receptors A chemosensor, also known as chemoreceptor, is a sensory receptor that transduces a chemical signal into an action potential. Or, more generally, a chemosensor detects certain chemical stimuli in the environment to simple sugars Sugar is an informal term for a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose characterized by a sweet flavor. In food, sugar almost exclusively refers to sucrose, which primarily comes from sugar cane and sugar beet. Other sugars are used in industrial food preparation, but are usually known by more specific from the decomposition of chitin. If chitin is detected, they then produce enzymes Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their to digest it by cleaving the glycosidic bonds In chemistry, a glycosidic bond is a type of functional group that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate in order to convert it to simple sugars and ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of.

Chemically, chitin is closely related to chitosan Chitosan is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It has a number of commercial and possible biomedical uses (a more water-soluble derivative of chitin). It is also closely related to cellulose Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units in that it is a long unbranched chain of glucose Glucose , a simple sugar (monosaccharide), is an important carbohydrate in biology. Cells use it as a source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and starts cellular respiration. Starch and cellulose are polymers derived from the dehydration of glucose. The name "glucose" comes derivatives. Both materials contribute structure and strength, protecting the organism.

Arabinoxylans

Arabinoxylans Arabinoxylans are the copolymers of two pentose sugars – arabinose and xylose. They are often inappropriately called hemicelluloses are the copolymers of two pentose A pentose is a monosaccharide with five carbon atoms. Pentoses are organized into two groups. Aldopentoses have an aldehyde functional group at position 1. Ketopentoses have a ketone functional group in position 2 or 3 sugars - arabinose Arabinose is an aldopentose – a monosaccharide containing five carbon atoms, and including an aldehyde functional group and xylose Xylose is a sugar. Specifically xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is the precursor to hemicellulose, one of the main constituents of biomass. Like most sugars, it can adopt several structures depending on conditions. With.

Acidic polysaccharides

Acidic polysaccharides are polysaccharides that contain carboxyl groups Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group, phosphate groups and/or sulfuric ester groups.

Bacterial polysaccharides

Bacterial polysaccharides represent a diverse range of macromolecules that include peptidoglycan, lipopolysaccharides, capsules and exopolysaccharides; compounds whose functions range from structural cell-wall components (e.g. peptidoglycan), and important virulence factors (e.g. Poly-N-acetylglucosamine in S. aureus), to permitting the bacterium to survive in harsh environments (e.g. Pseudomonas aeruginosa in the human lung).^[3] Polysaccharide biosynthesis is a tightly regulated, energy-intensive process and understanding the subtle interplay between the regulation and energy conservation, polymer modification and synthesis, and the external ecological functions is a huge area of research. The potential benefits are enormous and should enable for example the development of novel antibacterial strategies (e.g. new antibiotics and vaccines) and the commercial exploitation to develop novel applications.^[4][5]

Bacterial capsular polysaccharides

Pathogenic bacteria commonly produce a thick, mucous-like, layer of polysaccharide. This "capsule" cloaks antigenic proteins on the bacterial surface that would otherwise provoke an immune response and thereby lead to the destruction of the bacteria. Capsular polysaccharides are water soluble, commonly acidic, and have molecular weights on the order of 100-1000 kDa. They are linear and consist of regularly repeating subunits of one to six monosaccharides. There is enormous structural diversity; nearly two hundred different polysaccharides are produced by E. coli alone. Mixtures of capsular polysaccharides, either conjugated or native are used as vaccines.

Bacteria and many other microbes, including fungi and algae, often secrete polysaccharides as an evolutionary adaptation to help them adhere to surfaces and to prevent them from drying out. Humans have developed some of these polysaccharides into useful products, including xanthan gum, dextran, welan gum, gellan gum, diutan gum and pullulan.

Most of these polysaccharides exhibit interesting and very useful visco-elastic properties when dissolved in water at very low levels.^[6] This gives many foods and various liquid consumer products, like lotions, cleaners and paints, for example, a viscous appearance when stationary, but fluidity when the slightest shear is applied, such as when wiped, poured or brushed. This property is referred to as pseudoplasticity, or shear thinning.

Aqueous solutions of the polysaccharide alone have a curious behavior when stirred. After stopping, the swirl continues due to momentum, then stops, and then reverses direction briefly. This recoil demonstrates the elastic effect of the polysaccharide chains previously streched in solution, returning to their relaxed state.

Cell-surface polysaccharides play diverse roles in bacterial ecology and physiology. They serve as a barrier between the cell wall and the environment, mediate host-pathogen interactions, and form structural components of biofilms. These polysaccharides are synthesized from nucleotide-activated precursors (called nucleotide sugars) and, in most cases, all the enzymes necessary for biosynthesis, assembly and transport of the completed polymer are encoded by genes organized in dedicated clusters within the genome of the organism. Lipopolysaccharide is one of the most important cell-surface polysaccharides, as it plays a key structural role in outer membrane integrity, as well as being an important mediator of host-pathogen interactions.

The enzymes that make the A-band (homopolymeric) and B-band (heteropolymeric) O-antigens have been identified and the metabolic pathways defined.^[7] The exopolysaccharide alginate is a linear copolymer of β-1,4-linked D-mannuronic acid and L-guluronic acid residues, and is responsible for the mucoid phenotype of late-stage cystic fibrosis disease. The pel and psl loci are two recently discovered gene clusters that also encode exopolysaccharides found to be important for biofilm formation. Rhamnolipid is a biosurfactant whose production is tightly regulated at the transcriptional level, but the precise role that it plays in disease is not well understood at present. Protein glycosylation, particularly of pilin and flagellin, is a recent focus of research by several groups and it has been shown to be important for adhesion and invasion during bacterial infection.^[8]

See also

• Polysaccharide encapsulated bacteria
• Glycans
• Exopolysaccharide
• Beta-glucans
• Oligosaccharide Nomenclature

References

1. ^ Varki A, Cummings R, Esko J, Freeze H, Stanley P, Bertozzi C, Hart G, Etzler M (2008). Essentials of glycobiology. Cold Spring Harbor Laboratory Press; 2nd edition. ISBN 0-87969-770-9. http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=glyco2.
2. ^ Varki A, Cummings R, Esko J, Freeze H, Hart G, Marth J (1999). Essentials of glycobiology. Cold Spring Harbor Laboratory Press. ISBN 0-87969-560-9. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=glyco.TOC&depth=2.
3. ^ Sutherland, I. W. (2002). Vandamme, E. J., Ed.. ed. Polysaccharides from Microorganisms, Plants and Animals, in: Biopolymers, Volume 5, Polysaccharides I: Polysaccharides from Prokaryotes. Weiheim Wiley VCH. pp. 1–19. ISBN 978-3-527-30226-0.
4. ^ Ullrich M (editor) (2009). Bacterial Polysaccharides: Current Innovations and Future Trends. Caister Academic Press. ISBN 978-1-904455-45-5.
5. ^ Rehm BHA (editor). (2009). Microbial Production of Biopolymers and Polymer Precursors: Applications and Perspectives. Caister Academic Press. ISBN 978-1-904455-36-3.
6. ^ Viscosity of Welan Gum vs. Concentration in Water. http://www.xydatasource.com/xy-showdatasetpage.php?datasetcode=345115&dsid=80
7. ^ Guo H, Yi W, Song JK, Wang PG (2008). "Current understanding on biosynthesis of microbial polysaccharides". Curr Top Med Chem 8 (2): 141–51. doi:10.2174/156802608783378873. PMID 18289083.
8. ^ Cornelis P (editor). (2008). Pseudomonas: Genomics and Molecular Biology (1st ed.). Caister Academic Press. ISBN 978-1-904455-19-6 . http://www.horizonpress.com/pseudo.

External links

• Polysaccharide Structure
• Applications and commercial sources of polysaccharides
• European Polysaccharide Network of Excellence

Categories: Polysaccharides | Carbohydrate chemistry

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