Microtubules

Microtubules are hollow, cylindrical protein filaments that are a key component of the cytoskeleton in eukaryotic cells. They are involved in maintaining cell shape, intracellular transport, cell division, and the movement of cilia and flagella.

Structure:

• Made of tubulin dimers:
  • Each dimer consists of α-tubulin and β-tubulin subunits.
• Dimers assemble in a head-to-tail fashion to form protofilaments.
• 13 protofilaments align side-by-side to form the hollow tube.
• Microtubules are polarized:
  • Plus end (+): Fast-growing
  • Minus end (−): Slow-growing or anchored

Key Properties:

• Dynamic instability: Constantly grow and shrink by adding/removing tubulin dimers, especially at the plus end.
• Motor protein tracks: Used by kinesin (moves toward + end) and dynein (moves toward − end) to transport vesicles, organelles, and chromosomes.

Functions:

Specialized Microtubule Structures:

1. Centrosomes – Microtubule organizing centers (MTOCs) that nucleate microtubules using γ-tubulin.
2. Spindle apparatus – Microtubules that pull chromosomes apart during mitosis/meiosis.
3. Axonemes – Microtubule-based core of cilia and flagella, arranged in a 9 + 2 pattern (9 doublets + 2 central microtubules).

Microtubules vs. Other Cytoskeletal Elements:

Clinical Relevance:

• Cancer treatment: Drugs like taxol and vincristine disrupt microtubule dynamics to inhibit cell division.
• Neurodegenerative diseases: Dysfunction in microtubule transport can lead to conditions like Alzheimer’s disease (involving tau protein).
• Ciliary dyskinesia: Defects in microtubule structure in cilia can cause respiratory and fertility issues.

Summary Table: