What are Microtubules?
Microtubules are one of the three types of filaments that the cell's cytoskeleton adopts. Microtubules are the largest and provide structural support to the cell.
Eukaryotic cells (with a defined cell nucleus) have a cytoskeleton that provides the internal support that cells need to maintain their shape and other functions, such as, for example, assisting in cell mobility.
The elements of the cytoskeleton are made up of three types of protein fibers: microfilaments, intermediate filaments, and microtubules.
Microtubules have four basic functions:
- They give resistance to cells against compression forces, maintaining the shape of the cells, providing structural support.
- They form rails for motor proteins, such as kinesins and dyneins, that carry vesicles and other cargoes within the cell.
- They are responsible for the organization of the structure called the mitotic spindle, which separates the chromosomes during cell division or mitosis through the centrosomes.
In addition, they are key components of flagella and cilia, specialized structures of eukaryotic cells that aid movement, such as in sperm.
Structure of microtubules
Microtubules are the largest filaments of the three elements that make up the cytoskeleton of eukaryotic cells, measuring 25nm.
They are made of proteins called tubulins, which form a hollow tube. Tubulins are made up of two subunits: alpha-tubulin and beta-tubulin, which are the dimers of tubulin.
Microtubules are part of the structure of flagella, cilia where nine pairs of microtubules arranged in a circle can be observed, plus an additional pair in the center of the ring.
Microtubules also form centrioles, in this case, they are made up of nine microtubule triplets attached to supporting proteins. Two centrioles form a centrosome, structures that act as microtubule organizing centers in animal cells and that separate chromosomes during cell division.