Glucose residue, 1.6

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

Fig. 2. A representation of the cellulose chain ia solution, projected against three two-dimensional surfaces. The circles represent the oxygen atoms that link the iadividual glucose residues, and the lines take the place of the sugar residues. This result of a modeling study (39) iadicated a molecule somewhat more...

S. M., Okada, G. M., Sheldrick, G. M., Saenger, W., V-Amylose at Atomic Resolution X-Ray Structure of a Cycloamylose with 26 Glucose Residues (Cyclomalto-hexaicosaose). Proc.Nat.Acad.Sci.USA, 1999, 96, 4246. 

FIGURE 7.23 The starch phosphorylase reaction cleaves glucose residues from amy-lose, producing a-D-glucose-l-phosphate. 

A 0.2-g sample of amylopectin was analyzed to determine the fraction of the total glucose residues that are branch points in the structure. The sample was exhaustively methylated and then digested, yielding 50 /tmol of 2,3-dimethylglucose and 0.4 /tmol of 1, 2, 3, 6-tetramethylglucose. 

FIGURE 23.15 The reactions of glycogen debranching enzyme. Transfer of a group of three o -(l 4)-linked glucose residues from a limit branch to another branch is followed by cleavage of the o -(l 6) bond of the residue... 

Figure 7.5 Production of xanthan gum in batch culture using X. campestris. Bacterial dry weight ( ) xanthan gum ( ) residual glucose ( ) residual glutamate (A). Adapted from Microbial exopolysaccharide, Yenton etai pp 217-261. In biomaterials Novel Materials from Biological Sources, D Byrom (Ed), MacMillan Academic Professional Ltd, 1991.

Note. Examples of established usage of the -an ending are xylan for polymers of xylose, mannan for polymers of mannose, and galactan for polymers of galactose. Cellulose and starch are both glucans, as they are composed of glucose residues. 

Note that this is not a true triose but a trisaccharide containing three a-glucose residues. 

Figure 13-13. The glycogen molecule. A General structure. B Enlargement of structure at a branch point. The molecule is a sphere approximately 21 nm in diameter that can be visualized in electron micrographs. It has a molecular mass of 10 Da and consists of polysaccharide chains each containing about 13 glucose residues. The chains are either branched or unbranched and are arranged in 12 concentric layers (only four are shown in the figure). The branched chains (each has two branches) are found in the inner layers and the unbranched chains in the outer layer. (G, glycogenin, the primer molecule for glycogen synthesis.)...

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