Unit 2.1 Topic 5

Carbohydrates 3: structural units.

Beta-glucose molecules can be bonded together in a long chain, (polymer) through numerous condensation reactions, alpha-glucose molecules can also be condensed together to form coiled, spring like chains. Beta-glucose molecules have a slightly different shape from alpha-glucose molecules - when beta-glucose condenses, the resulting chains are long and straight.

These straight chain molecules can contain 10 000 beta-glucose molecules. They are stronger than the chains found in amylose. These beta-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 cell 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 from 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 substances called pectins, to form cell walls.

Structure and function of plant…