Medicine & USMLE


  1. Microfilaments (Actin Filaments)
  2. Intermediate Filaments
  3. Microtubules


Microtubules are cytoskeleton components that are made of two proteins, α-tubulin and ß-tubulin. They originate from centrosomes and serve three functions. First, they form the mitotic spindle of mitosis. Second, they make up cilia and flagella. Third, In nerve cells, they form a “railroad track” that motor proteins like kinesin and dynein travel on. Microtubules are also dynamic; they frequently lengthen and shorten.

Key Points

  • Microtubules
    • Cytoskeletal component
      • provides structural support, helps with cell movement and transport (vesicles, etc.) within the cell
      • Largest cytoskeletal component (diameter ~25 nm)
    • Originate from centrosomes
      • organelle that serves as the main microtubule organizing center (MTOC) of the animal cell
    • Made of α-tubulin and ß-tubulin
      • Dynamically unstable; frequently lengthen and shorten
        • Microtubules are capable of growing and shrinking in order to generate force
    • Function
      • Forms the mitotic spindle
        • Separates chromosomes (disjunction) toward opposite poles during anaphase, via attachment to centromere at kinetochore
        • Microtubule defects can lead to non-disjunction (non-separation of chromosomes in mitosis)
      • Make up cilia
        • Hair-like projections on cell exterior
      • Make up flagella
        • Tail-like projections that move the cell
      • Form a transport track for kinesin and dynein (motor proteins)
        • Helps move vesicles and other compounds around the cell