Polysaccharides

When a chain of monosaccharide units keeps growing — one condensation reaction after another adding a further sugar unit to the chain — the result is a very large molecule called a polysaccharide; this chain-building process is called polymerisation. Polysaccharides are correspondingly broken back down into their monosaccharide units by hydrolysis, and the physical properties of a given polysaccharide (its solubility, its mechanical strength, and so on) depend on the length of its chain and on how far it is branched, folded or coiled.

• Starch is the plant's reserve (storage) food, and exists in two forms, both built from α-glucose: amylose, an unbranched chain that coils into a helix and forms a colloidal suspension in hot water, and amylopectin, a branched polymer that is completely insoluble in water.
• Glycogen is, structurally, essentially amylopectin with much shorter distances between its branch points. It is the animal storage carbohydrate, stored chiefly in the liver and muscles, from where it is hydrolysed back to glucose as the body's energy needs demand.
• Cellulose is a polymer of β-glucose units arranged in straight, unbranched chains. It forms the cell wall of plant cells; the toughness of cellulose (far greater than that of a cell membrane) comes both from the way the glucose units are linked in the chain and from extensive hydrogen bonding between neighbouring cellulose chains. …