4.3—Starch, cellulose and cellulose microfibrils

Starch is a compact, insoluble storage polysaccharide of α-glucose. Cellulose is a structural polymer of β-glucose whose parallel chains form strong microfibrils through many hydrogen bonds.

Amylose is an unbranched helix with α-1,4 links; amylopectin has α-1,4 links plus α-1,6 branches, giving many terminal glucose units. Cellulose chains use β-1,4 links, so adjacent glucose units alternate orientation and align into fibres.

Starch granules can be stored without exerting a strong osmotic effect, then hydrolysed when glucose is needed. Cellulose microfibrils reinforce the wall so it withstands turgor pressure without bursting.

Starch and cellulose are both glucose polymers but their monomer configuration and bonding produce different functions. Hydrogen bonds between cellulose chains are not the same as the glycosidic bonds within each chain.