CYTOSKELETON:
-> It is a complex network of protein filaments and tubules that extend throughout the cytoplasm of eukaryotic cells.
-> It acts as the cell's internal framework, giving shape, structure and movement to the cell.
*STRUCTURE OF CYTOSKELETON:
*MAJOR COMPONENTS OF CYTOSKELETON:
1) MICROFILAMENTS :
-> Also called actin filaments.
-> They are the thinnest filaments, approx 7nm (nanometers) in diameter.
-> It is made up of Actin protein and are found beneath the plasma membrane, forming the cell cortex.
-> Its major function is to maintain cell shape and mechanical strength, which is responsible for cell movement (amoeboid movement, muscle contraction ).
-> It helps in cytoplasmic streaming in both plants and animals.
:(cytoplasmic streaming refers to the flow of cytoplasm within the cells)
-> It forms Microvilli for absorption.
{NOTE:
-> ENDOCYTOSIS - The process by which a cell takes in material from outside by engulfing it with its cell membrane.
-> EXOCYTOSIS - The process by which a cell sends material out of the cell by fusing a vesicle with the cell membrane. }
2) INTERMEDIATE FILAMENTS :
-> They are intermediate, approx 10nm in thickness.
-> They appear rope like which is made up of fibrous proteins such as ( keratin , vimentin , desmin , neurofilaments , nuclear lamins) .
-> They are more stable and less dynamic than microfilaments and microtubules.
-> Their main function is to provide mechanical strength and elasticity and maintain cell and nuclear shape.
-> They form the nuclear lamina (supports the nuclear envelope).
-> They help in anchoring organelles like the nucleus and desmosomes.
3) C- MICROTUBULES :
-> They have a hollow cylindrical shape, approx 25nm in diameter.
-> They are made up of Tubulin proteins ( ALPHA-TUBULIN and BETA-TUBULIN) dimers.
-> They radiate from the centrosome (microtubule organising centre).
-> They provide rigidity and structural support.
-> They form spindle fibres during cell division.
-> They serve as tracks for intracellular transport by using motor proteins.
-> They are made up of cilia and flagella for movement.
-> They form the structural basis of centrioles and basal bodies.
4) MOTOR PROTEINS:
A) KINESIN- It moves organelles towards the positive end of microtubules.
B) DYNEIN- It moves organelles towards the negative end of microtubules.
C) MYOSIN- Interacts with actin for muscle contraction and vesicle movement.
* FUNCTIONS OF CYTOSKELETON:
1) MAINTAIN CELL SHAPE AND STRUCTURE:- The cytoskeleton provides mechanical strength and maintains the shape of the cell. It forms a supportive framework beneath the plasma membrane, preventing the cell from collapsing or deforming.
2) ANCHORS ORGANELLES IN PROPER PLACE:- The cytoskeleton acts as an internal framework that holds various cell organelles such as the nucleus, endoplasmic reticulum, and mitochondria in fixed positions within the cytoplasm to maintain proper cellular organisation.
3) FACILITATES INTRACELLULAR TRANSPORT:- It forms tracks along which materials such as vesicles, proteins and organelles are transported inside the cell. Motor proteins like kinesin and dynein move along microtubules to carry substances to different parts of the cell.
4) ASSISTS CELL DIVISION:- During cell division, it plays an important role in separating the chromosomes. Microtubules form the mitotic spindle that ensures accurate distribution of genetic material to daughter cells.
5) GENERATES CELL MOVEMENT:- ( Cilia , flagella , pseudopodia )
The cytoskeleton is responsible for various types of cell movement. Microtubules form the structure of cilia and flagella, which help in locomotion, while Actin filaments assist in the formation of Pseudopodia for amoeboid movement.
6) PROVIDES MECHANICAL RESISTANCE TO DEFORMATION:- The cytoskeleton gives elasticity and mechanical support to the cell, allowing it to withstand external pressure or mechanical stress without losing its shape. This helps in maintaining the stability of cell structure.
7) INVOLVED IN SIGNAL TRANSDUCTION AND CELL COMMUNICATION:- The cytoskeleton plays a role in transmitting signals from the cell membrane to the interior. It helps the cell respond to external stimuli and communicate with neighbouring cells, coordinating different cellular activities.
Thus, the cytoskeleton acts as the dynamic internal framework of the cell, integrating structure, organisation, transport, division, movement, and communication to ensure proper functioning and survival of eukaryotic cells.
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