What is the Difference Between Actin Filaments and Microtubules?

Actin filaments and microtubules are both essential components of the cytoskeleton in eukaryotic cells, but they have distinct differences in their structure, function, and dynamics:

Structure:

Actin filaments are composed of actin subunits and have a diameter of about 7 nm. They are relatively flexible and consist of two parallel protofilaments that twist around each other.
Microtubules are composed of tubulin proteins (α-tubulin and β-tubulin) and have a diameter of about 25 nm. They are hollow cylinders and are strong and rigid.

Dynamics:

Actin filaments are dynamic and can grow and shrink rapidly. Their turnover is typically rapid, and they are influenced by various accessory proteins in a living cell.
Microtubules are also dynamic structures, growing and shrinking by the addition or removal of tubulin proteins.

Function:

Actin filaments determine the shape of the cell's surface, are essential for whole-cell locomotion, and serve as tracks for the movement of myosin motor proteins. They are also involved in cell division and cell movement.
Microtubules determine the positions of membrane-enclosed organelles and direct intracellular transport within cells. They also play an important structural role, helping the cell resist compression forces and maintain its shape.

Directionality:

Both actin filaments and microtubules have directionality, meaning they have two structurally different ends.

In summary, actin filaments are flexible and play crucial roles in cell movement and shape maintenance, while microtubules are rigid and serve as structural support and intracellular transport pathways. Both structures are essential for the proper functioning of cells and their processes, and their functions can be modulated by various accessory proteins within the cell.