Table of Contents
Cytoskeletal Proteins
All cells have a complex, dynamic network of interconnecting protein filaments known as the cytoskeleton. In different organisms, it is made up of identical proteins and stretches from the cell nucleus to the cell membrane. Its main job is to give the cell shape and mechanical resistance against deformation. Additionally, it stabilises whole tissues by interacting with external connective tissue and other cells.
There are three major types of cytoskeletal proteins found in eukaryotes:
- Microtubules
- Microfilaments
- Intermediate filaments
Microtubules
Two polypeptide subunits make up tubulin, and dimers of these subunits connect to form long strands of protofilaments. The hollow, straw-like filaments of microtubules are created by the union of 13 such protofilaments. Tubulin dimers are continually added to and removed from microtubules at both ends of the filament. One end, known as the plus end, grows more quickly than the other end, which is known as the negative end. The rates of change at either end are not equal. MTOCs or microtubule organising centres are the places in cells where microtubule minus ends are anchored. The centrosome, which is a cell’s main MTOC, is typically found close to the nucleus. Plasma membrane microtubules often extend from the centrosome.
Microtubules play a key role in the axoneme of flagella and cilia, formation of the mitotic spindle, synthesis of the plant cell wall and intracellular transports.
Microfilaments
Actin, also known as globular or g-actin, is a protein that is used to make microfilaments. G-actin is divided into two filamentous long strands. A microfilament is formed by the twisting together of these two strands. Microfilaments may be quickly assembled and removed and are dynamic. Treadmilling is the process of rapidly disintegrating microfilaments at one end and reassembling them at the other.
For cell motility, actin treadmilling is a crucial phenomenon. Together with the myosin protein, actin creates contractile units as well. Actin filaments are drawn closer together by myosin, which binds to and moves along them. Muscles can contract because of this. During cell division, actin and myosin also create the contractile ring, which eventually divides daughter cells into two during cytokinesis.
Cell movement, cytokinesis, maintenance of cell shape, muscle contraction and intracellular transport are some key functions of microfilaments.
Also Check:Difference between Cilia and Flagella
Intermediate Filaments
Although intermediate filaments appear in a variety of forms, they are typically rope-like structures. As a class, intermediate filaments are less dynamic than actin filaments or microtubules and serve mostly mechanical purposes. Microtubules and intermediate filaments frequently cooperate to give delicate tubulin structures stability and support. Although intermediate filaments are present in all cells, different protein components make up these structures. Some cells contain different kinds of intermediate filaments and some intermediate filaments are linked to particular kinds of cells. For instance, desmin filaments are only present in muscle cells, keratins are only present in epithelial cells and neurofilaments are only present in neurons. Vimentin filaments, for instance, are present in a variety of cell types and typically adjoin with microtubules. Similar to this, lamins are present in every type of cell, where they create a meshwork to support the inside nuclear membrane. Also, unlike actin or tubulin, intermediate filaments are not polar.
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