Function of Microtubules in Cell

In this function of microtubules in cell post we have briefly explained about microtubules in animal cell history, definition, components, functions and importance.

History

The cytologists like Freud (1882), Ballowitz (1890) and Meves (1910) observed filamentous components of the cytoplasm and referred these as fibrils. Later, with the improved microscopic techniques along with advancement made in the field of sectioning and staining, the ultra-structure of these components was revealed.

These were found to be tubular in nature (Burgos and Fawcett, 1955; Palay, 1960; Harris, 1962). De Robertis and Franchi (1953) reported the presence of microtubules in the axons of medullated nerve fibers and called them neurotubules. Slautterback in 1963 describes them to be associated with the developing nematocysts of Hydra and he proposed the name microtubules to these components.

Microtubules in Animal Cell

Microtubules in animal cell are microscopic hollow tubes made of the proteins alpha and beta tubulin that are part of a cell’s cytoskeleton, which is a network of protein filaments that extends throughout the cell, gives it shape, and holds its organelles in place. Microtubules, which are about 24 nanometers thick, are the largest structures in the cytoskeleton. They play important roles in cell movement, cell division, and material transport within cells.

Structure of Microtubule

Microtubule

Function of microtubules in animal cell: microtubules in animal cell are formed from dimer subunits of alpha ()- and beta ()-tubulin that arrange themselves into a hollow tube.

Microtubules in animal cell are hollow, unbranched cylinders, generally about 200 to 270 Å thick and several micrometers long.

They may occur singly or in bundles, and radiate from the centriole to the periphery of the cell. The microtubule is composed of 13 parallel protofilaments that run its entire length and enclose a central lumen about 150 Å wide.

Each proto-filament is made up of a row of globular subunits that have a diameter of about 40 to 50 Å. There may be cross bridges between adjacent microtubules.

Chemical Composition

Microtubules in animal cell are formed of a protein called tubulin. A tubulin subunit contains one α-tubulin molecule and one β-tubulin molecule. This αβ dimer is 80-100 Å long.

The α and β-tubulin molecules are arranged alternately in a helical manner. Many other proteins, called MAPs (microtubule associated proteins), form some 5 to 10 percent of the proteins of microtubules.

These proteins promote tubulin polymerization. A tubulin dimer has two GTP molecules bounded to it. One GTP is hydrolyzed to GDP when a tubulin dimer is incorporated into a microtubule. The α-β-α-β arrangement of the tubulin subunits gives polarity to the microtubule.

Function of Microtubules in Animal Cell

Form and support: microtubules in animal cell form a part of cytoskeleton which (a) maintains the shape of the cell and (b) provides mechanical support to the cell. This role of microtubules is especially evident in cells having long processes such as the axopodia of certain protozoans and axons of nerve cells. Red blood corpuscles of non-mammalian vertebrates are kept flat by peripheral band microtubules.

Movement: microtubules in animal cell form the motile elements of cilia and flagella. These bring about locomotion in protists and cause currents in the environment of animals.

Components of centriole and basal bodies: microtubules in animal cell are components of centriole and basal bodies. The centriole give rise to the mitotic spindle and the basal bodies produce cilia and flagella.

Formation of mitotic spindle: microtubules in animal cell forms the spindle and astral rays in cell division.

Chromosome movement: The chromosome fibers of spindle bring about movement of the chromosomes to the opposite poles of the cell in the anaphase.

Cell differentiation: microtubules in animal cell play a role in cell differentiation and determination of polarity.

Intracellular transport: Vesicles and protein molecules in the cell move along the “tracks” of microtubules. The movement is brought about by motor proteins kinesin and MAPIC (cytoplasmic dynin) powered by ATP.

Importance of Microtubules

Microtubules are very important for the cells as they provide internal framework serving as cytoskeleton to determine and maintain the cell form.

They also define pathway along which the particles move in cell. The mitotic apparatus consisting of spindle fibers and astral rays is in fact bundles of microtubules.

The generation of bending movements in cilia and flagella is attributed to a sliding microtubule mechanism

Further Readings

Reference