The Cytoskeleton

Most eukaryotic cells contain a complex network of protein fibers called the cytoskeleton. It forms a framework for the movement of organelles around the cytoplasm - most of the organelles are attached to the cytoskeleton. The network consists of protein microfilaments, intermediate filaments, and microtubules.

The cytoskeleton provides an important structural framework for:

1. Cell shape. For cells without cell walls, the cytoskeleton determines the shape of the cell. This is one of the functions of the intermediate filaments.
2. Cell movement. The dynamic collection of microfilaments and microtubles can be continually in the process of assembly and disassembly, resulting in forces that move the cell. There can also be sliding motions of these structures. Audesirk and Audesirk give examples of white blood cells "crawling" and the migration and shape changes of cells during the development of multicelled organisms.
3. Organelle movement. Microtubules and microfilaments can help move organelles from place to place in the cell. In the case of endocytosis when a vesicle is formed to engulf some particle from outside the cell, microfilaments attach to the vesicle and pull it into the cell. Much of the complex synthesis and distribution function of the endoplasmic reticulum and the Golgi complex makes use of transport vescicles, and it is thought that the movement of these vesicles is guided by the cytoskeleton.
4. Cell division. During cell division, microtubules accomplish the movement of the chromosones to the daughter nucleus. Then for animal cells, a ring of microfilaments helps divide the two developing cells by constricting the central region between the cells.