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Cytoskeleton – Definition, Structure, Functions 

Cytoskeleton Definition (What is a cytoskeleton?) Cytoskeleton Structure A cytoskeleton structure comprises the following types of fibres: 1. Microfilaments Functions of Microfilaments 2. Microtubules Functions ...

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Cytoskeleton Definition (What is a cytoskeleton?)

  • The cytoskeleton allows eukaryotic cells to change shape and perform coordinated, purposeful motions.
  • Microtubules, microfilaments (or actinfilaments), and intermediate filaments make up the cytoskeleton, which is a network permeating the whole cytoplasm (IFs).
  • The cytoskeleton supplies the machinery for cytoplasmic cyclosis and is directly engaged in a wide variety of cellular and organismal motions (such as cell motility, muscle contraction, and the various morphological changes that occur in a growing vertebrate embryo).
  • In contrast to prokaryotes, bacteria don’t appear to have a cytoskeleton, which suggests it played a key role in the development of eukaryotic cells.
  • The existence of an organised fibre array or cytoskeleton in the structure of the protoplasm was hypothesised in 1928 by Koltzoff.
  • He conceived of a cytoskeleton that determines both the shape of the cell and the changes in its form.
  • The primary proteins that are present in the cytoskeleton are tubulin (in the microtubules),actin, myosin, tropomyosin and other (in the microfilaments) and keratins, vimentin, desmin, lamin and others (in intermediate filaments) (in intermediate filaments).
  • Subunits of intermediate filaments are fibrous proteins, while tubulin and actin are globular proteins.
  • The isolation of these cytoskeletal proteins has made significant strides in recent years. The arrangement of microtubules and microfilaments may also be analysed using light and electron microscopy thanks to the development of specific antibodies against these proteins.
  • Evidence for the existence of a highly structured, three-dimensional lattice in the ground cytoplasm has also been provided by high-voltage electron imaging of entire cells.
Cytoskeleton
Cytoskeleton

Cytoskeleton Structure

A cytoskeleton structure comprises the following types of fibres:

  • Microfilaments
  • Microtubules
  • Intermediate Filaments

1. Microfilaments

  • Microfilaments, the thinnest component of the cytoskeleton, are employed to give the cell its form and sustain its interior organelles.
  • If a cell’s organelles were removed, the plasma membrane and cytoplasm would not be the only remaining components. There would still be ions and organic molecules within the cytoplasm, as well as a network of protein fibres that assist preserve the structure of the cell, secure organelles in precise places, allow cytoplasm and vesicles to move throughout the cell, and allow unicellular organisms to move independently.
  • This protein fibre network is known as the cytoskeleton.
  • Within the cytoskeleton, there are three types of fibres: microfilaments, intermediate filaments, and microtubules.
  • Microfilaments are the thinnest of the three types of protein fibres found in the cytoskeleton.
  • They function in cellular motility, have a diameter of around 7 nm, and are composed of two entwined actin filaments. Microfilaments are sometimes called as actin filaments for this reason.
Microfilaments
Microfilaments, which consist of two actin filaments entangled with one another, are the smallest filaments in the cytoskeleton. | Image Source: https://www.coursehero.com/study-guides/boundless-biology/the-cytoskeleton/

Functions of Microfilaments

  • Microfilaments facilitate cell mobility and are composed of the protein actin.
  • Myosin and actin collaborate to produce muscle contractions, cell division, and cytoplasmic streaming.
  • Microfilaments maintain the position of organelles within the cell.

2. Microtubules

  • Microtubules are a component of the cytoskeleton and assist the cell withstand compression, transport vesicles, and split chromosomes during mitosis.
  • Microtubules are, as their name implies, little hollow tubes. Microtubules, along with microfilaments and intermediate filaments, are categorised as cytoskeleton organelles.
  • The cytoskeleton is the framework that provides structural support for the cell.
  • Microtubules comprise the majority of the cytoskeleton.
  • The microtubule is composed of polymerized dimers of the globular proteins -tubulin and -tubulin.
  • With a diameter of around 25 nm, microtubules are the largest cytoskeleton components.
  • They assist the cell in resisting compression, offer a pathway for vesicle transport, and draw replicated chromosomes to opposing ends of a dividing cell. Microtubules, like microfilaments, can dissolve and rebuild rapidly.
  • Microtubules are structural components of flagella, cilia, and centrioles, as well (the latter are the two perpendicular bodies of the centrosome ).
  • The centrosome is the microtubule-organizing core in animal cells.
  • In eukaryotic cells, flagella and cilia are structurally distinct from their prokaryotic counterparts.
Micrtubule Structure
Micrtubule Structure: A microtubule’s wall is made up of 13 polymerized dimers of alpha- and beta-tubulin, making it hollow (right image). The left picture depicts the tube at the molecular level. . | Image Source: https://www.coursehero.com/study-guides/boundless-biology/the-cytoskeleton/

Functions of Microtubules

  • Microtubules aid the cell in resisting compression, offer a pathway for vesicles to travel within the cell, and are the building blocks of cilia and flagella.
  • Cilia and flagella are hair-like structures that aid in cell motility and line various structures to capture particles.
  • Cilia and flagella are composed of a “9+2 array,” which consists of a ring of nine microtubules encircled by two additional microtubules.
  • During cell division, microtubules bind to replicated chromosomes and pull them to opposing poles, allowing the cell to split with a complete set of chromosomes in each daughter cell.

3. Intermediate Filaments

  • Animal cells include intermediate filaments (IFs) as cytoskeletal components.
  • They consist of a family of similar proteins that share structure and sequence characteristics.
  • Intermediate filaments have an average diameter of 10 nanometers, which is between that of 7 nm actin (microfilaments) and that of 25 nm microtubules. However, they were originally labelled “intermediate” because their average diameter is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells.
  • Intermediate filaments contribute to cellular structural elements and frequently play a critical role in maintaining tissues such as skin together.

Functions of Intermediate Filaments

  • Intermediate filaments contribute to cellular structural elements and frequently play a critical role in maintaining tissues such as skin together.

Flagella and Cilia

  • Flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and are responsible for propelling the entire cell (for example, sperm, Euglena).
  • When flagella are present, the cell has only one or a few flagella. However, when cilia (singular = cilium) are present, many of them stretch along the entire plasma membrane surface.
  • They are short, hair-like structures utilised to transport complete cells (such as paramecia) or chemicals along the cell’s outer surface (for example, the cilia of cells lining the Fallopian tubes that move the ovum toward the uterus, or cilia lining the cells of the respiratory tract that trap particulate matter and move it toward your nostrils).
  • Despite their length and number disparities, flagella and cilia have a common microtubule arrangement known as a “9 + 2 array.”
  • A single flagellum or cilium consists of a ring of nine microtubule doublets around a single microtubule doublet at its core.

Many different types of motor proteins compose the cytoskeleton. Among these are:

  • Kinesin: Microtubules are responsible for transporting the various cellular components, and these proteins travel along them. They exert a pulling force on the organelles, dragging them parallel to the cell membrane.
  • Dyneins: The organelles in the cell are drawn closer to the nucleus by these.
  • Myosin: These trigger muscular contractions by interacting with actin protein. Cytokinesis, exocytosis, and endocytosis are also carried out by these cells.

Cytoskeleton Function (what is the function of the cytoskeleton?)

  • A framework capable of taking on the role of a cell’s shape guide while also withstanding forces that might otherwise alter that shape.
  • A structure inside the cell that is in charge of arranging all the various organelles. In polarised epithelial cells, where certain organelles are arranged in a preset order from the apical to the basal end of the cell, this role is emphasised.
  • Pathways within cells that guide the movement of molecules and organelles. Examples of this include the movement of messenger RNA (mRNA) molecules to their proper subcellular locations, the movement of membrane-bound carriers from the endoplasmic reticulum to the Golgi complex, and the movement of vesicles holding neurotransmitters along the length of a nerve cell. In the image, the brilliant green organelles, labelled peroxisomes (page 200), are shown to have robust connections with the red microtubules of the cytoskeleton. Peroxisome transport in mammalian cells takes place on microtubules.
  • The machinery responsible for producing force and moving cells around. Protruding locomotor organelles (cilia and flagella) that contain microtubules allow single-celled creatures to “crawl” across a solid substratum or “push” themselves through an aquatic environment. In multicellular organisms, cells such as sperm, white blood cells, and fibroblasts are capable of independent movement. The tip of an axon that is actively growing is also quite mobile; its motion is very similar to that of a crawling cell.
  • Important part of the machinery that divides cells. During mitosis, meiosis, and cytokinesis, components of the cytoskeleton are crucial for the segregation of chromosomes and the subsequent division of the parent cell into two daughter cells.

What is a Microtrabecular Lattice?

  • In recent years, it has been clear that the cytoplasm contains a micro-trabecular lattice, a three-dimensional network of interconnected filaments of cytoskeletal fibres.
  • It is this lattice that many cellular organelles, including ribosomes, lysosomes, and others, attach to for support.
  • Since the micro-trabecular lattice is malleable, the form of the cell also alters as the cell migrates.
Cytoskeleton
Cytoskeleton

Comparison Of Microtubules, Intermediate Filaments And Microfilaments

PropertyMicrotubulesIntermediate filamentsMicrofilaments
StructureHollow with walls made up of 13 protofilamentsHollow with walls made up of 4 to 5 protofilamentsSolid made up of polymerized actin (F-actin)
Diameter (nm)24-25107-9
Monomer unitsα- and β- tubulinFive types of protein defining five major classesG-actin
ATPase activityPresent in dynein armsNoneNone
Functions1. Motility of eukaryotes
2. Chromosome movement
3. Movements of intracellular materials
4. Contribute toward maintaining cell shape
1. Integrate contractile units in muscle
2. Cytoskeletal structural function in cytoplasm
1. Muscle contraction
2. Cell shape changes
3. Protoplasmic streaming
4. Cytokinesis

FAQ

What is the function of the cytoskeleton? or what does the cytoskeleton do?

Some of the major cytoskeleton duties are as follows:
It helps give the cell its form and structure.
Vacuole formation is aided by this factor.
Many parts of the cell are held in place by it.
It functions as a cell signalling aid.
It aids cellular processes like organelle transport, vesicle trafficking, and other intracellular processes.

Which of the following functions is NOT associated with the cytoskeleton in eukaryotic cells?
A. Intracellular transport
B. Maintenance of cell shape and structure
C. Support of the organelles
D. Cell motility
E. None of these

the correct option is E) None of the above.

What is a cytoskeleton?

Cells of all three kingdoms—eukaryotes, prokaryotes, and archaea—are built upon a framework called the cytoskeleton. These fibres in eukaryotic cells are made up of a tangled web of protein filaments and motor proteins that facilitate cell motility. It helps keep the cell together, keeps the organelles in their proper places, and allows for the movement of molecules, cell division, and the transmission of signals.

Where is the cytoskeleton located?

Cytoskeleton, a system of filaments or fibres that is present in the cytoplasm of eukaryotic cells (cells containing a nucleus).

What is the cytoskeleton made of?

The cytoskeleton of a cell is made up of microtubules, actin filaments, and intermediate filaments.

References

  • Stephen R. Bolsover, Elizabeth A. Shephard, Hugh A. White, Jeremy S. Hyams (2011). Cell Biology: A short Course (3 ed.).Hoboken,NJ: John Wiley and Sons.
  • Alberts, B. (2004). Essential cell biology. New York, NY: Garland Science Pub.
  • https://www.coursehero.com/study-guides/boundless-biology/the-cytoskeleton/

Citation

APA

MN Editors. (December 1, 2022).Cytoskeleton – Definition, Structure, Functions . Retrieved from https://microbiologynote.com/cytoskeleton/

MLA

MN Editors. "Cytoskeleton – Definition, Structure, Functions ." Microbiology Note, Microbiologynote.com, December 1, 2022.

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