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Cytoskeleton – Filaments, Structure and Functions

The latticework of microfilaments and microtubules is stated to operate as a cytoskeleton. Cytoskeleton is the cellular organelle present throughout the cytoplasm. It identifies the shape of the cell and provides assistance to the cell. It is a complex network of structures with differing sizes. In addition to identifying the shape of the cell, it is likewise important for the cellular movements and the response of the cell to external stimuli.

The 3 classes of cytoskeletal are based upon their size and the types of protein they consist of. In order of size, beginning with the thinnest, they are

  1. actin filaments (microfilaments)
  2. intermediate filaments
  3. microtubules

Cytoskeletal Filaments

Cell Parts
MicrotubulesHollow cylinders composed of protein; 25 nm in diameterSupport the cytoplasm and form centrioles, spindle fibers, cilia, and flagella
Actin filamentsSmall fibrils of the protein actin; 8 nm in diameterProvide structural support to cells, support microvilli, are responsible for cell movements
Intermediate filamentsProtein fibers; 10 nm in diameterProvide structural support to cells


Microtubules are the straight, hollow and tubular structures of the cytoskeleton. These organelles without the restricting membrane are set up in various packages. Each tubule has a size of 20 to 30 nm. Length of microtubule differs and it might be 1000 times more than the thickness.

Structurally, the microtubules are formed by packages of globular protein called tubulin Tubulin has 2 subunits, specifically a-subunit and p-subunit.

Functions of Microtubules

Microtubules might operate alone or accompany other proteins to form more complex structures like cilia, flagella or centrioles and carry out numerous functions Microtubules:

  1. Identify the shape of the cell
  2. Provide structural strength to the cell
  3. Imitate conveyer belts which enable the movement of granules, vesicles, protein molecules and some organelles like mitochondria to various parts of the cell
  4. Form the spindle fibers which separate the chromosomes throughout mitosis
  5. Are accountable for the movement of centrioles and the complex cellular structures like cilia.

Intermediate Filaments

Intermediate filaments are the structures that form a network around the nucleus and encompass the periphery of the cell. Size of each filament has to do with 10 nm. The intermediate filaments are formed by rope-like polymers, which are composed of fibrous proteins

Subclasses of intermediate Filaments

Intermediate filaments are divided into 5 subclasses:

  1. Keratins (in epithelial cells)
  2. Glial filaments (in astrocytes)
  3. Neurofilaments (in nerve cells)
  4. Vimentin (in numerous types of cells)
  5. Desmin (in muscle fibers).

Functions of Intermediate Filaments

Intermediate filaments assist to keep the shape of the cell. These filaments likewise link the surrounding cells through desmosomes.


Microfilaments are long and great thread-like structures with a size of about 3 to 6 nm. These filaments are composed of non-tubular contractile proteins called actin and myosin. Actin is more plentiful than myosin.

Microfilaments exist throughout the cytoplasm. The microfilaments present in ectoplasm consist of just actin molecules and those present in endoplasm consist of both actin and myosin molecules.

Functions of Microfilaments


  1. Provide structural strength to the cell
  2. Supply resistance to the cell versus the pulling forces

    Are accountable for cellular movements like contraction, gliding and cytokinesis (partition of cytoplasm throughout cellular division).

[su_spoiler title=”References” style=”fancy” icon=”chevron”]http://www.sciencedirect.com/science/article/pii/0968000484901373 http://www.annualreviews.org/doi/pdf/10.1146/annurev.bi.63.070194.002021 http://nar.oxfordjournals.org/content/early/2010/02/05/nar.gkq037.short [/su_spoiler]

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