Structure: How do they work?
All eukaryotic cells produce the protein tubulin, of which there are two types, alpha and beta. Alpha and beta tubulin spontaneously bind one another to form a functional subunit that we call a heterodimer. A heterodimer is a protein that consists of two different gene products. (the prefix hetero- means "different," the prefix di- means "two," and the suffix -mer refers to a unit, in this case a single polypeptide).
When intracellular conditions favor assembly, tubulin heterodimers assemble into linear protofilaments. Protofilaments in turn assemble into microtubules.
Microtubules form a framework for structures such as the spindle apparatus that appears during cell division, or the whiplike organelles known as cilia and flagella. Cilia and flagella are the most well-studied models for microtubule structure and assembly, and are often used by textbooks to introduce microtubules.
Function: What They Do
Microtubules are involved in cell structure. Together with microfilaments and intermediate filaments, they make up the cytoskeleton. They also make up the structure of the cilia and flagella, and help the movement of organelles. Nine sets of microtubule triplets make up centrioles, which help in cell reproduction.
