The cytoskeleton consists of three well-defined filamentous structures microtubules, actin filaments, and intermediate filaments.

Functions

A dynamic scaffold to provide structural support and shape.
An internal framework for positioning organelles within the cell interior.
Tracks that direct the movement of materials
Motors derived from force generating apparatuses within the cell.
- These motors move along tracks in the cytoskeleton, and while doing so they undergo conformational changes that fuel their motion.
Mechanisms that facilitate cell division, in particular, separating the chromosomes and splitting the cell.

Composition

Tough, ropelike fibers made of a variety of similar fibrous proteins. They provide mechanical strength to cells subjected to physical stress.
- These proteins start as monomers, then dimers which are assembled into polymers in a side-by-side staggered manner anti-parallel to each other.
- The growth of the filament is done in the interior of the filament rather than its ends.
- The assembly and disassembly of IFs are controlled by phosphorylation and dephosphorylation of its subunits.
These are not polarized so they would not be able to guide the motor via polarity.
- Additionally, they tend to be less sensitive to chemical agents than other types of cytoskeletal elements.
- They also tend to be insoluble.
They often radiate through the cytoplasm and are interconnected via thin cross bridges usually made of plectin. Plectin consists of binding sites for an intermediate filament on one end and a cytoskeletal structure on the other.
Connecting the IFs to the whole cytoskeleton also allows it to serve as a scaffold for organizing the cell’s structure and absorbing mechanical stresses. Thus IFs are important in tissue-specific functions rather than basic cellular functions.

Movement of motile cells display a similar sequence of activities:
- Movement is initiation by the protrusion of a part of the cell surface in the direct in which the cell is to move.
- A portion of the lower surface of the protrusion attaches to the substratum, forming temporary sites of anchorage
- The bulk of the cell is pulled forward over the adhesive contacts, which eventually become part of the rear of the cell
- The cell breaks its rear contacts with the substratum, causing retraction of the trailing edge, or “tail.”
The lamellipodium is a broad, flattened, veil like protrusion that is the leading edge of the motile cell. It provides temporary anchorage to the substratum.
Movement involves assembly and disassembly of actin via actin-binding proteins.
- As a cell migrates, it generates pulling forces against its substrate.
- This causes a protrusion to form. Myosin then pulls the remaining parts of the cell.