Formation and Fate of Cell Organelles

Many large, ordered biological structures, such as the coats of virus particles, muscle filaments, microtubules, and bacterial flagella, consist of a large number of protein subunits, but the number of different types of subunits is in general small. In fact, in many protein structures there may be only one type of subunit. Examples of highly ordered biological structures made up of subunits which are, or at least appear to be, identical are the protein coats of tobacco mosaic and turnip yellow mosaic viruses, the actin and myosin filaments of muscle, and the microtubules of cilia and of the mitotic spindle. Some of these structures can be dissociated into their components, and the intact components can in turn be reassembled under appropriate conditions in vitro to produce a structure
which appears to be the same as, or at least very similar to, the original organized structure assembled in vivo.