Motor proteins are a class of molecular motors that can move along the cytoskeleton of cells. They convert chemical energy into mechanical work by the hydrolysis of ATP. Flagellar rotation, however, is powered by a proton pump.
The action of myosin along the actin filaments causes the shortening and lengthening of the sarcomere; responsible for muscle contraction and relaxation, respectively.
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components: microfilaments, intermediate filaments, and microtubules, and these are all capable of rapid growth or disassembly depending on the cell's requirements.
The cytoskeleton consists of (a) microtubules, (b) microfilaments, and (c) intermediate filaments.
Actin cytoskeleton of mouse embryo fibroblasts, stained with phalloidin
Microtubules in a gel-fixated cell
Cross section diagram through the cilium, showing the “9 + 2” arrangement of microtubules