Shapes of macromolecules and lateral association orientation. The figures (i) and (ii) show the two different plausible shapes used to represent the protofibrils along with their appropriate dimensions. In the past these molecules have been represented as spheres for the most part. Based on experimental observations we suggest that a prolate spheroidal shape is more appropriate. Figure (iii) indicates the association mechanism of two spheroidal molecules. Since the ratio , we can effectively assume that the association of two spheroids creates another spheroid with major and minor axes c and 2b, respectively.