Microtubule

Tubulin Infographic

Microtubules in the leading edge of a cell

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FluorescentCells

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Microtubule

Diagram of a microtubule structure

Microtubules are cytoskeletal structures found in the cytoplasm of eukaryotic cells. They are composed of tubulin proteins and play a crucial role in maintaining cell shape, enabling cellular motility, and facilitating intracellular transport. Microtubules are also essential for cell division, particularly during the processes of mitosis and meiosis.

Structure

Microtubules are cylindrical tubes with an outer diameter of approximately 25 nanometers and an inner diameter of about 15 nanometers. They are composed of alpha-tubulin and beta-tubulin dimers that polymerize to form a hollow tube. The polymerization and depolymerization of tubulin dimers are dynamic processes regulated by GTP hydrolysis.

Functions

Microtubules serve several critical functions within the cell:

• Cell Shape and Support: They provide structural support to the cell, helping to maintain its shape.
• Intracellular Transport: Microtubules act as tracks for the movement of organelles and vesicles within the cell, facilitated by motor proteins such as kinesin and dynein.
• Cell Division: During mitosis and meiosis, microtubules form the mitotic spindle, which is essential for the segregation of chromosomes into daughter cells.
• Cell Motility: Microtubules are components of cilia and flagella, which are involved in cell movement and fluid flow across cell surfaces.

Dynamics

Microtubules exhibit dynamic instability, characterized by phases of growth and shrinkage. This dynamic behavior is crucial for their functions, particularly in cell division and intracellular transport. The regulation of microtubule dynamics is influenced by various microtubule-associated proteins (MAPs) and post-translational modifications of tubulin.

Microtubule-Associated Proteins (MAPs)

MAPs are proteins that interact with microtubules to regulate their stability and function. Some well-known MAPs include:

• Tau protein: Associated with neurodegenerative diseases such as Alzheimer's disease.
• MAP2: Found in neurons and involved in stabilizing microtubules in dendrites.
• MAP4: Ubiquitously expressed and involved in stabilizing microtubules in various cell types.

Clinical Significance

Microtubules are targets for several anticancer drugs, such as taxanes and vinca alkaloids, which disrupt microtubule dynamics and inhibit cell division. Abnormalities in microtubule function are also implicated in various diseases, including neurodegenerative disorders and cancer.

See Also

• Cytoskeleton
• Actin filament
• Intermediate filament
• Cell division
• Mitosis
• Meiosis
• Kinesin
• Dynein