Polysaccharide



  Polysaccharides are relatively complex amorphous, insoluble in water, and have no sweet taste.

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

Examples include storage polysaccharides such as chitin.

Polysaccharides have a general formula of Cn(H2O)n-1 where n 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 n={40...3000}.

Storage polysaccharides

Starches

Starches are glucose polymers in which glucopyranose units are bonded by alpha-linkages. It is made up of a mixture of Amylose and Amylopectin. Amylose consists of a linear chain of several hundred glucose molecules and Amylopectin is a branched molecule made of several thousand glucose units.
Starches are insoluble in water. They can be digested by hydrolysis, catalyzed by enzymes called corn are major sources of starch in the human diet.

Structural polysaccharides

Cellulose

The structural component of plants are formed primarily from polymer 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.

Acidic polysaccharides

Acidic polysaccharides are polysaccharides that contain ester groups.

Bacterial capsule 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 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 dextran, gellan gum, and pullulan.

Cell-surface polysaccharides play diverse roles in the bacterial "lifestyle". They serve as a barrier between the cell wall and the environment, mediate host-pathogen interactions, and form structural components of 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.[1]

See also

  • Polysaccharide encapsulated bacteria
  • Glycans

References

Sutherland, I. W. (2002) Polysaccharides from Microorganisms, Plants and Animals, in: Biopolymers, Volume 5, Polysaccharides I: Polysaccharides from Prokaryotes (Vandamme, E. J., Ed.), Weiheim: Wiley VCH, pp. 1-19. ISBN: 978-3-527-30226-0

  1. ^ Cornelis P (editor). (2008). Pseudomonas: Genomics and Molecular Biology, 1st ed., Caister Academic Press. ISBN 978-1-904455-19-6 . 
General: Aldose | Ketose | Pyranose | Furanose
Geometry: Triose | Tetrose | Pentose | Anomer | Mutarotation
Small/Large: Erythrulose | Sedoheptulose
Trioses: ketotriose | Aldotriose
Tetroses: Erythrulose | Erythrose | Threose
Pentoses: Xylose | Xylulose
Hexoses: Rhamnose
Disaccharides: Maltose
Polymers: Dextrin
Glycosaminoglycans: Heparan sulfate | Dermatan sulfate | Keratan sulfate
Aminoglycosides: Amikacin


homopolysaccharides : glucansbe-x-old:Полісахарыды

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Polysaccharide". A list of authors is available in Wikipedia.