MicrotubulesMicrotubules Definition and Examples

Fibroblast cells showing cytoskeleton
Fibroblast cells showing cytoskeleton. DR TORSTEN WITTMANN/SCIENCE PHOTO LIBRARY Science Photo Library/Getty Images

Definition

Microtubules are fibrous, hollow rods, that function primarily to help support and shape the cell. They also function as routes along which organelles can move throughout the cytoplasm. Microtubules are typically found in all eukaryotic cells and are a component of the cytoskeleton, as well as cilia and flagella. Microtubules are composed of the protein tubulin.

Microtubules and Cell Movement

Microtubules play a huge role in movement within a cell.

They form the spindle fibers that manipulate and separate chromosomes during the mitosis phase of the cell cycle. Examples of microtubule fibers that assist in cell division include polar fibers and kinetochore fibers.

Microtubules also form cell structures called centrioles and asters. Both of these structures are found in animal cells, but not plant cells. Centrioles are composed of groupings of microtubules arranged in a 9 + 3 pattern. Asters are star-shaped microtubule structures that form around each pair of centrioles during cell division. Centrioles and asters help to organize the assembly of spindle fibers, which move chromosomes during cell division. This ensures that each daughter cell gets the correct number of chromosomes after mitosis or meiosis. Centrioles also compose cilia and flagella, which allow for cell movement as demonstrated in sperm cells and cells that line the lungs and female reproductive tract.

Cell movement is accomplished by the dis-assembly and re-assembly of actin filaments and microtubules. Actin filaments or microfilaments are solid rod fibers that are a component of the cytoskeleton. Motor proteins, such as myosin, move along actin filaments causing cytoskeleton fibers to slide along side one another.

This action between microtubles and proteins produces cell movement.