Structure and Function of Microtubules

Microtubules are conveyer belts inside the cells. They move vesicles, granules, organelles like mitochondria, and chromosomes via special attachment proteins. They also serve a cytoskeletal role. Structurally, they are linear polymers of tubulin which is a globular protein. These linear polymers are called protofilaments. The figure to the left shows a three dimensional view of a microtubule. The tubulin molecules are the bead like structures. They form heterodimers of alpha and beta tubulin.  A protofilament is a linear row of tubulin dimers.

Microtubules may work alone, or join with other proteins to form more complex structures called cilia, flagella or centrioles . In this unit we will cover all of these structures.  Read the Chapter on Microtubules in Lodish.

Note: many of the photos are from the text, or from Histology texts by Bloom and Fawcett used by our students.  They are for illustration at this site only and for individual student use.

Test yourself!! What do you already know about microtubules, cilia, and centrioles?

  • What is the structural subunit of a microtubule?
    Why is the temperature important during assembly of a microtubule and what ingredients would you need to make a microtubule?
  • What would happen if you substituted a nonhydrolyzable analog of GTP for the GTP? What clue does this give you about the role of GTP?
  • With respect to microtubules, what is dynamic instability and why is it important to the cell?
  • What is the GTP cap and how could the cell use it to regulate microtubule growth?
  • How do Microtubule associated proteins help with the functional differentiation of a cell? Think about your past studies of neurons, for example. How might microtubules organize different functional domains? What about polarized cells, like the intestinal epithelial cell?
  • What are kinesins and dyneins and how do they work?
    What in vitro experiments are used to detect direction of movement along the microtubules?
  • Which drugs would you use to stabilize microtubules?
  • Which would you use to prevent mitoses? Why are some of these drugs useful in the treatment of cancer?
  • What are cilia and flagella and what is the basic difference in structure between the two?
  • How are cilia and flagella structured to be mobile? What is an "axoneme"?
  • What is the role of dynein in the movement of cilia and flagella?
  • What is the role of nexin and the radial spokes in the movement of cilia and flagella? What will happen if you were to digest the nexin and radial spokes with proteases?
  • Why are centrioles important to cilia function? What are basal bodies?
  • How is the internal structure of centrioles and cilia or flagella different?
  • How do centrioles control the direction of the ciliary beat?
  • How do centrioles replicate?

For the lecture on microtubules, we will discuss the following paper:  Bloom, GS and Goldstein, LSB 1998 Cruising along Microtubule Highways: How Membranes Move Through the Secretory Pathway. J Cell Biology 140: 1277-1280

  1.  What controversy led to this commentary?
  2.  How important are microtubules to Rapid vesicle transport in Neurons?
  3.  What experiments led to the finding that Transport from ER to Golgi occurs along microtubules?
  4.  What conditions lead to secretion in the absence of microtubules?
  5.  Are there some transport steps that do not require microtubules?
  6.  How do the authors use the evidence in the literature to explain the controversy?
Last updated: 04/02/03
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Gwen V. Childs, Ph.D. or

text copyright 1996 Gwen V. Childs, Ph.D.