On the Molecular Structure of Starch Granules

It is a problem how to fit the molecules of amylose and amylopectin into the ultrastructural apposition layers of starch granules which have a width of only 0.1μ. Stretched amylose chains with a length up to 1 μ can be ruled out. In addition to the proposal of Miihlethaler, who visualizes folded amylopectin chains, a model with a helical amylose chain is discussed. A helix with six glucose residues per turn would be compatible with the crystal lattice found by Kreger; and the disorder caused by this helix in the hexagonal lattice of the parallel side chains of the amylopectin would account for the low optical anisotropy of the starch granules as compared to the parallel β‐polyglucosan chains in cellulose. The proposed model, fitted into the 0.1 μ apposition ring of the starch granule, shows tangential strata with a layer repeat of about 80 A and a radial chain lattice with the fibre period 10.6 A; i.e., it shows a combination of a lamellar and a fibrous structure.