In this article we will discuss about the Structure and Function of Microtubules and Cytoskeleton in Cell.
Structure of Microtubules and Cytoskeleton in Cell:
Microtubules are long, hollow tubular cylinders with an outer diameter of 250Å. The wall thickness is about 50Å, leaving a hollow core of about 150Å diameter. The length of microtubules varies from a fraction of a micron to several microns.
A transverse section of a cytoplasmic microtubule shows 13 subunits (protofilaments) which lie parallel to the long axis of the microtubule. The proto-filament appears to be made up of a linear series of globular protein (tubulin) units, like a string of beads.
Tubulin is a dimer composed of two similar, but not identical, polypeptides. The two subunits of a tubulin dimer are called α-tubulin and β-tubulin (Fig. 2.62). The α- and β-tubulin units are arranged alternately in the proto-filament.
The basic arrangement of tubulin appears to be helical, with 13 tubulin molecules per turn of the helix. In addition to the tubulins there are about 20 to 25 secondary proteins which have been termed microtubule- associated proteins (MAPs). They are of importance in the function of microtubules and in the control of assembly.
Function of Microtubules and Cytoskeleton in Cell:
Since microtubules are fairly rigid they form a supporting framework or cytoskeleton and give shape to the cell. Microtubules, making up the axial support of cilia and flagella, are involved in movement. The spindle fibres of mitotic and meiotic spindles consist of bundles of microtubules.
According to the currently favoured assembly-disassembly hypothesis, shortening of kinetochore microtubules by disassembly and/or elongation of microtubules of continuous fibres by assembly provides the force for chromosome movement during anaphase.