What structural difference accounts for the functional differences between starch and cellulose? a) starch can be digested by animal enzymes, whereas cellulose cannot. b) starch and cellulose differ in the glycosidic linkages between their glucose monomers. c) starch is a polymer of glucose, whereas cellulose is a polymer of fructose.

Both starch and cellulose are glucose polymers, but the glycosidic linkages in these two polymers differ, as shown in Figure 5.7. Glucose can have two slightly different ring structures. When glucose forms a ring, the hydroxyl group attached to the number 1 carbon is positioned either below (alpha)or above (beta) the plane of the ring. In starch, all the glucose monomers are in the alpha configuration (Figure 5.7b). In cellulose, all the glucose monomers are in the beta configuration. As a result, every other glucose monomer is "upside down" with respect to its neighbors (Figure 5.7c). The differing glycosidic linkages in starch and cellulose give the two molecules distinct three-dimensional shapes, leading to key functional differences.

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