Carbohydrate polymers – structural units:
β-glucose molecules can be bonded together in a long chain (polymer) through numerous condensation reactions, α-glucose molecules can also be condensed together to form coiled, spring like chains. β-glucose molecules have a slightly different shape to α-glucose molecules- when β-glucose condenses; the resulting chains are long and straight.
These straight chain molecules can contain 10,000 β-glucose molecules. They are stronger than the chains found in amylose. These β-glucose polymer chains are called cellulose chains. Cellulose is found only in plants. It is the most abundant structural polysaccharide in nature.
Cellulose fibres are arranged in a very specific way to form plant call walls. Because the glucose monomers contain so many OH groups, many hydrogen bonds can form between them. About 60-70 cellulose molecules become cross-linked by hydrogen bonds to form bundles called microfibrils. These in turn are held together by more hydrogen bonds to form larger bundles called macrofibrils. The macrofibrils have great mechanical strength- close to that of steel. They are embedded in a polysaccharide glue of substance called pectin, to form cell walls.
Structure and function…