Microtubules- Definition, Structure, Functions and Diagram


Microtubules are one of the three main components of the cytoskeleton, which is the network of protein filaments that gives shape and support to eukaryotic cells. The other two components are microfilaments and intermediate filaments. Microtubules are the largest and most rigid of the three, with a diameter of about 25 nanometers (nm).

Microtubules are composed of tubulin, a globular protein that forms dimers of two subunits: alpha-tubulin and beta-tubulin. These dimers are arranged in a helical pattern to form long hollow tubes called protofilaments. Each microtubule has 13 protofilaments that run parallel to its axis and form a cylindrical wall. The wall has a thickness of about 5 nm and a central lumen of about 15 nm.

Microtubules have polarity, meaning that they have two structurally and functionally distinct ends: the plus end and the minus end. The plus end is where tubulin dimers are added or removed more rapidly than at the minus end, making it the site of dynamic growth and shrinkage. The minus end is more stable and often anchored to a microtubule-organizing center (MTOC), such as a centrosome or a basal body.

Microtubules are highly dynamic structures that can undergo rapid assembly and disassembly in response to cellular signals and needs. This process is called dynamic instability and involves cycles of growth, pause, and catastrophe (sudden depolymerization). Dynamic instability allows microtubules to explore the cytoplasm and interact with various cellular components and organelles.

Microtubules play important roles in many cellular processes, such as cell division, intracellular transport, cell motility, cell signaling, and cell shape maintenance. They also form the core of specialized structures, such as cilia, flagella, centrioles, basal bodies, and mitotic spindles. Microtubules are regulated by various factors, such as microtubule-associated proteins (MAPs), motor proteins (such as kinesin and dynein), GTP hydrolysis, calcium ions, and drugs (such as colchicine and taxol).

In summary, microtubules are hollow cylindrical tubes made of tubulin dimers that form part of the cytoskeleton and participate in many cellular functions. They have polarity, dynamic instability, and diverse interactions with other molecules and structures in the cell.