Beta-glucose

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Beta-glucose is a cyclic, six carbon sugar, formed from glucose, and can polymerise to make cellulose, an essential polysaccharide used in the structure of plants.

Glucose is a simple monosaccharide, chemical formulae: C6H12O6, and is an important carbohydrate which can provide energy or structure to organisms through its various forms [1].

In glucose, carbons 2, 3, 4 and 5 each have a hydroxyl group, and the direction these groups come off their chiral carbon decides the type of monosaccharide. Two of the combinations give the two glucose stereoisomers: D and L. These two isomers are mirror images of each other [2]. Other arrangements of the hydroxyl groups give different sugars, and all of these different sugars are epimers of each other.

Glucose can form a cyclic structure by a reaction between C1 and C2. The cyclic version can come in two forms for each type of glucose: alpha and beta[3]. These two isomers exist because the formation of cyclic glucose creates an asymmetric carbon at C1. This stereoisomerism at C1 is the cause for the two forms.

<span style="line-height: 1.5em;" />Repeated condensation reactions between C1 and C4 of two D-beta-glucose molecules forms a covalent glycosidic bond, creating a disaccharide, and with further polymerising can form cellulose - the most abundant organic molecule on Earth [4].

Cellulose is formed by 1,4 glycosidic bonds between hundreds of D-beta-glucose molecules and hydrogen bonds between the layers of the polysaccharide. This creates a highly organised crystalline structure, which plants use to maintain cell wall structure. Cellulose can be hydrolysed with enzymes back to glucose.[5]

References:

  1. HyperPhysics (2013) Sugars. Available at: http://hyperphysics.phy-astr.gsu.edu/hbase/organic/sugar.html (last accessed 14.11.2103)
  2. Biotopics. Molecular structure of glucose and other carbohydrates. Available at: http://www.biotopics.co.uk/as/glucose2.html (last accessed 14.11.2013)
  3. Biotopics. Molecular structure of glucose and other carbohydrates. Available at: http://www.biotopics.co.uk/as/glucose2.html (last accessed 14.11.2013)
  4. Klemm, Dieter et al (6 September 2005). "Cellulose: Fascinating Biopolymer and Sustainable Raw Material". ChemInform 36 (36). doi:10.1002/chin.200536238
  5. Virtual Chembook (2003)Cellulose. Available at: http://www.elmhurst.edu/~chm/vchembook/547cellulose.html (last accessed 14.11.2013)
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