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<p><strong>Polysaccharides</strong> (sometimes called <em><html><a title="Glycans" href="http://en.wikipedia.org/wiki/Glycans">glycans</a></html></em>) are relatively complex <html><a title="Carbohydrate" href="http://en.wikipedia.org/wiki/Carbohydrate">carbohydrates</a></html>.</p>
<p>They are <html><a title="Polymer" href="http://en.wikipedia.org/wiki/Polymer">polymers</a></html> made up of many <html><a title="Monosaccharide" href="http://en.wikipedia.org/wiki/Monosaccharide">monosaccharides</a></html> joined together by glycosidic linkages. They are therefore very large, often branched, molecules. They tend to be amorphous, insoluble in water, and have no sweet taste.</p>
<p>When all the constituent monosaccharides are of the same type they are termed <em>homopolysaccharides</em>; when more than one type of monosaccharide is present they are termed <em>heteropolysaccharides</em>.</p>
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<li class="toclevel-1"><a href="http://en.wikipedia.org/wiki/Polysaccharide#Starches"><span class="tocnumber">1</span> <span class="toctext">Starches</span></a> </li> <li class="toclevel-1"><a href="http://en.wikipedia.org/wiki/Polysaccharide#Glycogen"><span class="tocnumber">2</span> <span class="toctext">Glycogen</span></a> </li> <li class="toclevel-1"><a href="http://en.wikipedia.org/wiki/Polysaccharide#Cellulose"><span class="tocnumber">3</span> <span class="toctext">Cellulose</span></a> </li> <li class="toclevel-1"><a href="http://en.wikipedia.org/wiki/Polysaccharide#Acidic_polysaccharides"><span class="tocnumber">4</span> <span class="toctext">Acidic polysaccharides</span></a> </li> <li class="toclevel-1"><a href="http://en.wikipedia.org/wiki/Polysaccharide#Bacterial_Capsule_Polysaccharides"><span class="tocnumber">5</span> <span class="toctext">Bacterial Capsule Polysaccharides</span></a> </li>
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<h2>Acidic polysaccharides</h2>
<p>Acidic polysaccharides are polysaccharides that contain <html><a title="Carboxyl group" href="http://en.wikipedia.org/wiki/Carboxyl_group">carboxyl groups</a></html>, phosphate groups and/or <html><a class="new" title="Sulfuric ester group" href="http://en.wikipedia.org/w/index.php?title=Sulfuric_ester_group&action=edit">sulfuric ester groups</a></html>.</p>
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<h2>Bacterial Capsule Polysaccharides</h2>
<p>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 <html><a title="Molecular weight" href="http://en.wikipedia.org/wiki/Molecular_weight">molecular weights</a></html> on the order of 100-1000 <html><a title="Atomic mass unit" href="http://en.wikipedia.org/wiki/Atomic_mass_unit">kDa</a></html>. They are linear and consist of regularly repeating subunits of one ~ six monosaccharides. There is enormous structural diversity; nearly two hundred different polysaccharides are produced by <html><a title="Escherichia coli" href="http://en.wikipedia.org/wiki/Escherichia_coli">E. coli</a></html> alone. Mixtures of capsular polysaccharides, either <html><a title="Conjugate vaccine" href="http://en.wikipedia.org/wiki/Conjugate_vaccine">conjugated</a></html> or native are used as vaccines.</p>
<p>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 <html><a title="Xanthan gum" href="http://en.wikipedia.org/wiki/Xanthan_gum">xanthan gum</a></html>, <html><a title="Dextran" href="http://en.wikipedia.org/wiki/Dextran">dextran</a></html>, gellan gum, and <html><a title="Pullulan" href="http://en.wikipedia.org/wiki/Pullulan">pullulan</a></html>.</p>