Structure of Starch

Starch is packed into semicrystalline granules (containing crystalline and non-crystalline section) called starch granules. These granules are either contained in plant leaves or stored for long term usage in the plant's seeds/roots/fruit. In the leaves, the starch granules are smaller and are located inside chloroplasts. This starch is termed transitory starch and is accessed during the night to provide the plant with energy. The granules contained in the plant's other organs hold starch referred to as storage starch which is reserved for long-term usage. These granules are stored inside special double-envelopped organelles called amyloplasts. Potato tubers contain this type of starch and are used as the potato plant's "battery" when the shoot of the plant has died and thus can not provide the plant with any energy (glucose) via photosynthesis.

The structure of starch granules has been debated and it's not yet clear. Nevertheless, scientists have identified some components. As the two polymers that make up starch are just repeated glucose molecules, starch consists only of glucose. Amylose is polymerized into a coiled chain of glucose molecules (no branching), while amylopectin shows a linear but branched structure. The granules consist of 10-30% amylose (percentage varies depending on source) and 70-90% amylopectin. The branched chains of amylopectin interact together and form double helices while the linear part of amylopectin that is not surrounded by its branches resides together with amylose chains. These amylose chains form the amorphous (non-crystalline) part of the granules while the packed double helices form the crystalline one.