Figure 2. Schematic Diagrams of the Myosin Molecule, Filament and Insertions (not drawn to scale). (A) Diagram of a myosin molecule showing the globular head region, the α-helical coiled-coil rod and the short non-helical tail (NHT). The subfragment-1 (S-1), rod and heavy meromyosin (HMM) proteolytic domains are also indicated. (B) An example of a bipolar filament, which is formed by interaction among the rod domains. The in vitro bipolar filament contains an average of 29, 30 and 14 molecules respectively for NM II-A, II-B and II-C.⁵ Note the significantly smaller size of the II-C filament. (C) Exclusion or inclusion of two alternative insertions at the myosin head increases the total isoforms of NM II-B and II-C to 4 each.