Organisation and Properties of the Striated Muscle Sarcomere

Two principal attributes of living cells are that they can produce active movement, at least within their cytoplasm, and that they can reproduce themselves. Following the work of Watson and Crick (1953), Franklin and Gosling (1953) and Wilkins et al. (1953), the mechanism of reproduction at the molecular level in terms of DNA replication and its consequences have become increasingly well defined, but the molecular mechanisms involved in cell movement are much less clear. In fact, molecular movements are themselves a key feature of reproduction: for example, in the flagella-driven swimming of sperm and in both the migration of chromosomes and the pinching off of the two daughter cells at the contractile ring during cell division. Other aspects of movement occur in cytoplasmic streaming, in amoeboid movement and in the wavelike motions of cilia. However, the clearest of all manifestations of movement is in the contraction of muscular tissue, either in the continuous beating of heart muscles or in the voluntary motions of skeletal muscles.