The structure and function of cytoskeleton are discussed below.
What is cytoskeleton?
The cytoskeleton is made up of two words “cyto” and “skeleton”. “Cyto” means “cytoplasm” which is a thick liquid present inside the cell while the “skeleton” means “framework”. The cytoskeleton is a framework of filaments and tubules present inside the cytoplasm giving shape and support to the cell. It works the same way inside the cell as the skeleton in the human body. The cytoskeleton is only present in the cytoplasm and absent in the nucleus. The cytoskeleton was first discovered in 1903 by Nikolai K. Koltsov and present in both eukaryotic and prokaryotic cells.
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| Structure of cytoskeleton. Image created in BioRender.com |
Structure and function of cytoskeleton
The cytoskeleton is made up of three main types of filaments.
- Microfilaments
- Microtubules
- Intermediate filaments
Video lesson
1. Microfilaments
In microfilaments, “micro” means “small” and “filament” means “a slender threadlike object or fibre”. Microfilaments, also known as actin filaments, are small fibres made up of actin protein. Two parallel strands of actin proteins are arranged in a helical shape to form microfilaments. Microfilaments are the thinnest and about 7 nm in diameter.
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| Structure of microfilament |
Function of microfilaments
Microfilaments are involved in
- Cell division
- Cell motility or movement
- Cytoplasmic streaming (movements of organelles and nutrients from one part of a cell to another through cytoplasm)
- Contraction and relaxation of muscles (In muscle cell, actin filaments work together with myosin filaments in contraction and relaxation of muscles)
- Maintain the shape of the cell
2. Microtubules
In microtubules, “micro” means “small” and “tubules” means “a hollow cylinder or tube”. Microtubules are hollow tubes like structure made up of tubulin protein. There are two types of tubulin proteins found in microfilaments i.e., alpha (α) tubulin and beta (β) tubulin, which are spirally and alternatively arranged in a tube-like structure. Microtubules are the thickest and about 23-27 nm in diameter.
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| Structure of microtubules |
Functions of microtubules
The main functions of microtubules are:
- These are present in flagella and cilia and help in their movement
- They form mitotic spindle and helps in the division of chromosomes during cell division
- Transport of different molecules from one part of a cell to another
- Cell wall synthesis in plants
3. Intermediate filament
In intermediate filament, "intermediate" means “coming between two things”. So, intermediate filaments are present in between microfilaments and microtubules in terms of size. Intermediate filaments are 8 to 12 nm in diameter. The composition of intermediate filament varies according to their function and location. For example, intermediate filament present in hair or nail cells contains keratin protein. One end of filament has carboxyl term, while other end has amino terminal.
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| Structure of intermediate filaments |
Functions of Intermediate filament
The main functions of intermediate filaments are:Maintain the shape of the cell
- Allows cell to bear external pressure or mechanical stresses
- Provides support and strength to the cell
- Involve in the cell to cell and cell to matrix junctions
- Comparison of microfilaments, intermediate filament, and microtubules.
Comparison of microfilaments, intermediate filament, and microtubules
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Parameters |
Microfilaments |
Intermediate
filament |
Microtubules |
|
Size |
Thin |
Intermediate |
Thick |
|
Diameter
(nm) |
7 |
12 |
23-27 |
|
Composition |
Actin protein |
Vary according to its presence (hair/nail contains keratin protein and Neurofilament proteins in neuron) |
Tubulin protein (α and β) |
|
Position |
Near cell membrane |
Extends from nucleus to the cell membrane |
Near nucleus |
Functions of cytoskeleton
Overall, the functions of the cytoskeleton are:
- It helps in the maintenance of the shape of a cell and prevents its deformation
- It plays important role in the internal organization of cell organelles
- It helps in the cell division and movement of chromosomes to the opposite poles of the cell during meiosis
- It provides mechanical strength to the animal cell as animal cells lack a cell wall
- Cytoplasmic streaming which is helpful in the movement of important substances from one part of the cell to another part is also controlled by the cytoskeleton
- In unicellular organisms, the presence of cytoskeleton in cilia and flagella aids in the movement of organisms
Some questions and answers
1. Why cytoskeleton is important?
A. The cytoskeleton is a framework of filaments and tubules present inside the cytoplasm and provides shape and support to the cell. It works the same way inside the cell as the skeleton in the human body.
A. There are three types of cytoskeleton i.e., Microfilaments, Microtubules, and Intermediate filament.
3. Is the cytoskeleton present in prokaryotes?
A. Yes, the cytoskeleton is present in both prokaryotic and eukaryotic cells. Without the cytoskeleton, a cell can not perform its function properly.
4. Which cell lack a cytoskeleton?
A. All types of cells including animal cells, plant cells, unicellular, prokaryotes and eukaryotes contain cytoskeleton. No cell lacks a cytoskeleton.
5. Which protein makes microfilaments?
A. Microfilamntes are small fibres made up of actin protein.
6. Which protein makes microtubules?
A. Microtubules are hollow tubes-like structure made up of tubulin protein. There are two types of tubulin proteins found in microfilaments i.e., alpha (α) tubulin and beta (β) tubulin.
7. What are the three important functions of the cytoskeleton?
A. It helps in the maintenance of the shape of a cell, helps in the internal organization of cell organelles and helps in the cell division and movement of chromosomes to the opposite poles of the cell during meiosis.
8. Which type of cytoskeleton is present in cilia and flagella?
A. Microtubules are present in cilia and flagella. Microtubules are tube-like structure and slide along each other to provide movement to the cell.
9. Which type of protein makes intermediate filament?
A. The composition of protein forming intermediate filament varies according to their function and location. For example, intermediate filament present in hair or nail cells contains keratin protein.
10. Are microtubules or microfilaments bigger?
A. Microtubules are bigger compared to microfilaments. The diameter of microtubules is 23-27 nm, while microfilaments are 7 nm in diameter.
11. Where is the Microfilament located?
A. Microfilaments are present near the cell membrane of a cell and help in the maintenance of cell shape.
12. Where are the Microtubules located?
A. They are present near the nucleus of a cell and help in the formation of mitotic apparatus during cell division.
- Bretscher, A. (1991). Microfilament structure and function in the cortical cytoskeleton. Annual review of cell biology, 7(1), 337-374.
- Birchmeier, W. (1984). Cytoskeleton structure and function. Trends in Biochemical Sciences, 9(4), 192-195.
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