Microtubules
Microtubules are hollow cylindrical structures that play a vital role in providing support and shaping the cell, as well as serving as pathways for the movement of organelles. These structures are found in all eukaryotic cells and vary in length, with an approximate diameter of 25 nanometers. They are composed of building blocks known as tubulin and are more rigid than microfilaments. Microtubules are essential for the proper segregation of daughter chromosomes during cell division and form bundles that create cilia and flagella in unicellular organisms and certain multicellular animal cells.
Microfilaments
Microfilaments are thin, solid rods that are actively involved in muscle contraction, primarily found in muscle cells. Like microtubules, microfilaments are present in nearly all eukaryotic cells and are predominantly made of the protein actin. They facilitate the movement of organelles and exist as a network or bundles of parallel fibers within the cell.
As the thinnest components of the cytoskeleton, microfilaments range in diameter from 5 to 9 nanometers. Their functions include providing structural support to the cell and participating in cell movement. Certain cells can elongate microfilaments in the direction they wish to move, pushing the cell membrane forward, which aids the cell in exploring its environment or responding to specific signals. Microfilaments are also crucial for muscle contraction as they serve as pathways for the protein myosin.
Intermediate Filaments
Intermediate filaments are present in many cell types and provide support to both microfilaments and microtubules by anchoring them in place. These filaments include keratin found in epithelial cells and neurofilaments in nerve cells. With a diameter of approximately 10 nanometers, intermediate filaments are larger than microfilaments, thicker, and stronger. There are various types of intermediate filaments, each composed of different proteins, and some body parts, such as hair and nails, consist entirely of these filaments made from keratin.
In contrast to actin filaments and microtubules, intermediate filaments are highly stable structures that form the true framework of the cell. They anchor the nucleus and maintain its position within the cell, contributing to the cell’s flexibility and ability to withstand mechanical stress. Additionally, intermediate filaments play a role in connecting tissues, as they are crucial for the tight association of various tissue types, including epithelial tissues that line organs and surround muscles.