Starch is the major energy storage molecule in plants.
It is formed of two polysaccharides, both made of $$\alpha$$-glucose:
- Amylose only contains 1-4 glycosidic bonds. It has an unbranched structure.
- Amylopectin has a branched structure. The $$\alpha$$-glucose monomers are linked by 1-4 and 1-6 glycosidic bonds.
Amylose and amylopectin combine to give starch a spiral structure with some branching. This structure is relevant to its energy storage role:
- Starch is dense and insoluble. This reduces the space needed for storing starch.
- The spiral structure with branching makes starch readily accessible to enzymes. This means the starch can be broken down rapidly when energy is needed in the cell.
Plant cells contain organelles called amyloplasts which convert glucose into starch for storage.