By Jennifer Raymond April 14, 2004 Chapter 20 Microtubules By Jennifer Raymond April 14, 2004

What is a microtubule? A microtubule is a polymer of globular tubulin subunits, heterodimers of - and -tubulin, which are arranged in a cylindrical tube. They are twice the width of an intermediate filament and three times the width of a microfilament. Their length varies from a fraction of a micrometer to hundreds of micrometers. Microtubules are stiff which give it the ability to generate pushing forces without buckling.

Microtubule Assembly

Microtubule Disassembly

Movement Along Microtubules Kinesins Moves from the (+) end to the (–) end of a microtubule.

Dynein Dyneins (–) end-directed motor proteins that bind cargo through the protein dynactin.

Cilia and Flagella

Microtubules in Mitosis

Chromosome Capture Prometaphase

Moving into Metaphase

Microtubule Shortening Anaphase A

Spindle Elongates Anaphase B

Microtubules in Mitosis

Conclusion Microtubules take part in cell movements, including the beating of cilia and flagella and the transport of vesicles in the cytoplasm. These movements result from the assembly and disassembly of microtubules or the actions of microtubule motor proteins. Microtubules are crucial to the alignment and separation of chromosomes in mitosis.

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