CYTOSKELETON:
-> It is a complex network of protein filaments and tubules that extend throughout the. cytoplasm of eukaryotic cells .
-> It acts as "cell's internal framework" giving shape , structure and movement to the cell.
*STRUCTURE OF CYTOSKELETON:
*MAJOR COMPONENTS OF CYTOSKELETON:
1) MICROFILAMENTS :
-> Also called as actin filaments .
-> They are the thinnest filaments approx 7nm (nanometers) in diameter.
-> It is made up of Actin protein and is found beneath the plasma membrane forming cell cortex .
-> It's 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 cell takes in material from outside by engulfing them 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 most stable and less dynamic than microfilaments and microtubules .
-> Their main function is to provide mechanical strength and elasticity, maintain cell and nuclear shape.
-> They form nuclear lamina (supports nuclear envelope).
-> They help in anchoring organelles like nucleus and desmosomes .
3) C- MICROTUBULES :
-> They have 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 serves as tracks for intracellular transport by using motor transport.
-> They are made up of cilia and flagella for movement.
-> They form 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 action 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 nucleus , endoplasmic reticulum , and mitochondria , in fixed positions within cytoplasm to maintain proper cellular organization.
3) FACILIATES INTRACELLULAR TRANSPORT:- It forms tracks along which materials such as the 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 type of cell movement . Microtubules form the structure of cilia and flagella , which help in locomotion , while Actin filaments assist in 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 stability of cell structure .
7) INVOLVED IN SIGNAL TRANSDUCTION AND CELL COMMUNICATION:- The cytoskeleton plays a role in transmitting signals from cell membrane to interior . It helps cell's response to the 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, organization, transport, division, movement, and communication to ensure proper functioning and survival of eukaryotic cells.
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