Polysaccharides

James N BeMiller, Purdue University, Indiana, USA

Published online: September 2009

DOI: 10.1002/9780470015902.a0000693.pub2

Polysaccharides are carbohydrate polymers containing from approximately 35 (usually more than 100) to as many as 60 000 monosaccharide units. Polysaccharides have a range of general structures (from linear to various branched structures) and shapes. They are structural components of cell walls of bacteria, fungi, algae and higher plants and of the exoskeletons of insects and crustaceans, are energy- and carbon-storage substances, and serve various other functions as extracellular materials of plants, animals and microorganisms. They are the most abundant (by mass) of all organic substances in living organisms, comprising about two-thirds of the dry weight of the total biomass. Some have commercial value as isolated substances.

Key concepts

  • Polysaccharides are polymers of sugar (carbohydrate) units.
  • Polysaccharides are ubiquitous in nature. They are present in all plant tissues.
  • Polysaccharides comprise about three-fourths of the total biomass on Earth.
  • Polysaccharides serve as structural materials, as reserve food materials and in other functions.
  • Polysaccharides occur in a wide range of shapes and sizes.
  • Polysaccharides are hydrophilic and either dissolve in or absorb water.
  • Polysaccharides are produced and used commercially in large volumes.

Keywords: polysaccharides; glycans; gums

Figure 1. Repeating unit structure of cellulose showing how the -d-glucopyranosyl units are joined by (14) glycosidic linkages. The carbon and hydrogen atoms bonded to the carbon atoms are omitted for clarity. The carbon atoms of each glycosyl unit are numbered, C1 being the anomeric carbon atom (the one on the extreme right of each unit in this structure), C2 being the carbon atom attached to C1, C3 being the next and so on to C6 in this case. The oxygen atoms attached to each carbon atom are numbered O1, O2, O3, and so on. A cellulose molecule will contain approximately 150–5000 of these repeating units. The right-hand end (the reducing end) will be terminated in an –OH group, making the structure a hemiacetal (a potential aldehydo group) and that end the reducing end. The left-hand end (the non-reducing end) will be terminated in a –H atom.
Figure 2. Portions of polysaccharide molecules showing the different kinds of branching. indicates the reducing end.
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 Further Reading
    book Aspinall GO (ed.) (1982) The Polysaccharides, vol. 1. New York, NY: Academic Press.
    book Aspinall GO (ed.) (1983) The Polysaccharides, vol. 2. New York, NY: Academic Press.
    book Aspinall GO (ed.) (1985) The Polysaccharides, vol. 3. New York, NY: Academic Press.
    BeMiller JN (1999) Structure–property correlations of non-starch food polysaccharides. Macromolecular Symposia 140: 1–15.
    book Klemm D, Philipp B, Heinze T, Heinze U and Wagenknecht W (1998) Comprehensive Cellulose Chemistry, vols 1 and 2. Weinheim, Germany: Wiley VCH.
    book Shimizu K (1991) "Chemistry of hemicelluloses". In: Hon DN-S and Shiraishi N (eds) Wood and Cellulosic Chemistry. New York, NY: Marcel Dekker.
    book Suzuki M and Chatterton NJ (eds) (1993) Science and Technology of Fructans. Boca Raton, FL: CRC Press.
    book Varki A, Cummings R, Esko J et al. (1999) Essentials of Glycobiology. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.
    book Walter RH (ed.) (1991) The Chemistry and Technology of Pectin. San Diego, CA: Academic Press.
    book Whistler RL and BeMiller JN (2009) Starch: Chemistry and Technology. Orlando, FL: Academic Press.

Related Sub-Topics:

General Structural Biology | Other Biomolecules: Structure, Function, Metabolism
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Article Title: Polysaccharides
 
How to Cite close
BeMiller, James N(Sep 2009) Polysaccharides. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000693.pub2]