Cytoskeleton: Definition, Types, Examples, Diagram, Functions, Structure

Cytoskeleton Definition

Cytoskeleton refers to the network of protein fibres that help in maintaining the shape of the cell and help in the movement of the cell.

What is a cytoskeleton?

It is a network of protein filaments and tubules present in the cytoplasm of eukaryotic cells. It was initially thought of as having only a role in maintaining cell shape, but its functions extend to enabling intracellular transport, facilitating cell division, and supporting cellular movements. Therefore, the cytoskeleton forms a key role in cellular biology.

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Cytoskeleton Structure

Different components of the Cytoskeleton are:

Microfilaments (Actin Filaments)

• These are the narrowest fibres, made up of two intertwined strands of F-actin protofilaments. They are also called actin filaments.

• F-actin protofilaments are made up of G-actin subunits.

• F-actin is the filamentous actin, while G-actin is the globular actin.

• The individual strands of F-actin protofilaments are wound together with the help of tropomyosin.

• Tropomyosin is a double-stranded alpha-helical coiled-coil protein.

• It bears a protein complex, called troponin, which is interspersed along the length of the coil.

• Microfilaments provide shape and rigidity to the cells. They can depolymerise (disassemble) and reform quickly, thus enabling a cell to change its shape and move.

Intermediate Filaments

• They are called intermediate filaments because their diameter (8 to 10 nm) is between microfilaments and microtubules.

• These are structural in function.

• They do not perform any role in the movement.

• They maintain the shape of the cell by bearing the tension.

• Their main function is to maintain the shape of the cell and provide tensile strength.

• These are formed through the process of polymerization.

Microtubules

• These are small hollow tubules.

• Their walls are made up of polymerised dimers of a-tubulin and B-tubulin.

• They have a diameter of 25 nm. They are the widest component of the cytoskeleton.

• They help the cell resist compression, provide a track along which vesicles move through the cell and pull replicated chromosomes to opposite ends of a dividing cell.

• Like microfilaments, microtubules can dissolve and reform quickly.

Diagram

The given diagram shows the structure of the different types of cytoskeleton.

Functions of the Cytoskeleton

Cell Shape and Mechanical Support

• Provides a structural framework, maintaining the cell’s shape.

• Actin filaments form a cortical network beneath the plasma membrane.

Role in providing mechanical strength

• Intermediate filaments distribute mechanical stress across the cell.

• Microtubules resist compression and help maintain cell rigidity.

Intracellular Transport

• Mechanisms of transport along microtubules and actin filaments.

• Vesicles and organelles are transported along microtubules via motor proteins.

• Actin filaments facilitate short-range transport within the cell.

Role of motor proteins (kinesin, dynein, myosin)

• Kinesin moves cargo towards the plus end of microtubules (away from the nucleus).

• Dynein moves cargo towards the minus end of microtubules (towards the nucleus).

• Myosin transports cargo along actin filaments; involved in muscle contraction and various cellular processes.

Cytoskeleton and Cell Signaling

Interaction with Cell Membranes

The cytoskeleton is linked to the plasma membrane by a variety of proteins. It is important for the maintenance of the cell shape and provides a scaffold for interactions with the outside world. This linkage also serves as a basis for signal transduction pathways. It involves receptors in the membrane that then activate the cytoskeleton to serve in information processing by turning those signals into action, which in turn affects cellular responses.

Response to External Stimuli

The ability of cytoskeleton structures to reorganize themselves in response to mechanical or chemical signals allows the cell to adapt according to these changes. An example is the dynamic response needed during processes such as migration, division, and differentiation. It enables the cell to respond appropriately to any external stimulus it faces.

Cytoskeleton in Disease

Many diseases are associated with cytoskeletal defects. Neurodegenerative diseases, Alzheimer's and Parkinson's diseases, are diseases characterized by neuronal loss resulting from defects in microtubules and actin filaments. In cancer, mutations affecting the components of this system cause uncontrolled cell division and metastasis. Knowledge of these defects has contributed to our understanding of these disorders and may be important in developing targeted treatments.

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Experimental Techniques to Study the Cytoskeleton

Various experimental techniques to study the cytoskeleton are explained below.

• Various microscopy techniques, such as fluorescence microscopy, and electron microscopy, among others, are used.

• These give a detailed visualisation of cytoskeletal structures.

• The techniques also include the fractionation and purification of proteins to isolate the cytoskeletal proteins.

• Western blotting is a highly sensitive biochemical method to detect proteins.

• Genetic approaches, such as gene knockouts and RNA interference, also provide a way to identify roles for specific cytoskeletal proteins.

Conclusion

The cell shape is maintained evidently by the cytoskeleton. It supports intracellular transport. Then, a range of cellular movements is facilitated, including cell division and even cell movement. The cell membranes, interactions, and intercellular signalling have been important in terms of the functions of the cytoskeleton.

Future studies will help in the further development of mechanisms of cytoskeletal regulation. The development of therapies that could correct cytoskeletal defects. As imaging and genetic techniques continue to improve, we will learn even more about this critical cellular component.