Principles of Biochemistry, Volume 1 - A. Lehninger 1985

Biomolecules
Cells
Microfilaments, microtubules, and the microtrabecular network form the cytoskeleton

In many Eukaryotic Cells, various types of microfilaments and microtubules together form a flexible framework known as the Cytoskeleton. Recently, a third component of the cytoskeleton has been discovered—the microtrabecular lattice (see the photograph at the beginning of this chapter). This Structure was revealed using a high-voltage Electron microscope with exceptionally high resolving power. Before this method was applied, the microtrabecular lattice could only be observed as an unresolved Background referred to as the ground substance of the Cytoplasm. The microtrabecular lattice consists of very thin, interlaced filaments whose chemical composition is not yet known, though they almost certainly contain Proteins. The precise three-dimensional Organization and function of the microtrabecular lattice in various cells are currently under active investigation.

Class="center">

Fig. 2-17. A. Electron micrograph of the fibrous cytoskeleton of a fibroblast. B. Schematic representation of the fibroblast cytoskeleton. The long tubes are microtubules, and the thinner elements are various types of microfilaments.

The cytoskeleton gives cells their characteristic appearance and shape, serves as an attachment site for intracellular Organelles and various bodies—fixing their positions within The Cell—and facilitates communication between the cell's various components. The cytoskeleton should not be viewed as a rigid, permanent structural framework, but rather as a dynamic, time-dependent structure. Microtubules, for instance, are constantly assembled from their constituent parts and subsequently disassembled. The structure of the human fibroblast cytoskeleton is shown schematically in Fig. 2-17.