To the heart of myofibril assembly

One of the most fascinating examples of cytoskeletal assembly is the myofib ril, the contractile structure of striated (i.e. skeletal and cardiac) musc le. Myofibrils are composed of repeating contractile units known as sarcome res, perhaps the most highly ordered macromolecular structures in eukaryoti c cells. When skeletal and cardiac muscle cells differentiate, thousands of structural and regulatory molecules assemble into the semicrystalline sarc omeric contractile units. As a consequence of this precise assembly, many d ifferent classes of proteins function together to convert the molecular int eractions of actin ann myosin efficiently into the macroscopic movements of contractile activity.