Microtubules: Definition, Structure, & Examples

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Microtubules Definition

Cytoskeleton are the cytoplasmic structures, which are present in eukaryotes and maintains the cell shape, responsible for transportation and locomotion. Cytoskeleton is of three types; intermediate filaments, microfilaments and microtubules.

What are Microtubules?

Intermediate filaments consist of two stranded structure which are opposite to each other and consists of various subunits, having a diameter between 8-12nm. Microtubules is a helical structure composed of actin subunit.

Microtubules, Microtubules Definition, Microtubules Function, What are Microtubules,

Microtubules as the name suggests are tubulin in structure, which have polarity and a length of 200nm to 25µm with a diameter of 25nm. Intermediate filaments functions are maintaining the cell shape, anchoring organelles, bounding cell from cell and etc. Movement, cytoplasmic streaming, contraction of muscle, transportation of substances and cytokinesis are the functions of microfilaments.

The functions of microtubule are movement, generation of spindle fiber and maintenance of shape. Intermediate filaments example are glial cells, vimentin and keratin. Example of microtubules are alpha and beta tubulin. Microfilament example is the actin filament.

Microtubules Features

The structural component of cytoplasm are the microtubules. These microtubules consist of alpha and beta tubulin polymers, which forms a dimer. The thickness of this structure is 5nm and the length is between 200nm-25µm, with a diameter of 25nm. The lumen lies within the microtubule’s hollow space. As there are alpha and beta tubulin dimers, they possess polarity, alpha tubulin has negative polarity and beta tubulin possess positive polarity.

The centers of the microtubule are the basal bodies and centrioles. To the cytoskeleton microtubules, various proteins are attached. Proteins like kinesin and dynein are the motor proteins, which are bound to microtubule and other regulatory proteins and severing proteins like katanin.

Microtubules Types

Microtubules are further categorized into kinetochore microtubules, these spread from the kinetochore protein centrosome to the chromosome’s centromere. Polar microtubules spread throughout the cell from centrosome to centrosome. Astral microtubules extend from spindle fibers to cell membrane.

Microtubules Polymerization

The alpha and beta tubular proteins polymerizes resulting in the formation of a protofilament which is linear. 13 protofilaments when placed laterally forms a hollow microtubule structure. The length of microtubules could be increased by addition of alpha and beta dimers; thus, the length will differ. In eukaryotes, there are 13 microtubules, whereas in prokaryotes there are five microtubules. 9+2 type of microtubule pattern is seen in cilia and flagella.

Microtubules Function

There are various functions which are carried out by this cytoplasmic structure, microtubule. Transportation of vesicles, organelles and cytoplasmic structures is carried out by microtubules.

Microtubules, Microtubules Definition, Microtubules Function, What are Microtubules, 2

The formation of spindle fiber is also under their control where the chromosome move to the opposite poles, while dividing. Other functions are locomotion, maintaining shape and structure. Microtubules are considered as the component of flagella, cilia and cytoskeleton.

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