Table of Contents
Definition
noun
plural: cytoskeletons
cy·to·skel·e·ton
(cell biology) The lattice or internal framework of a cell composed of protein filaments and microtubules in the cytoplasm, and has a role in controlling cell shape, maintaining intracellular organization, and in cell movement
Details
Overview
A cell is the structural, functional and biological unit of all organisms. In eukaryotes, the cell contains cytoplasmic structures. One of them is the cytoskeleton.
Features
A cytoskeleton a cytoplasmic structure that forms the lattice or internal framework of a cell. It is composed of protein filaments and microtubules. It extends throughout the cytosol, from the nucleus to the plasma membrane. Its primary function is associated with cell shape, division, differentiation, intracellular organization, and cell movement. It occurs in all cells of living things, particularly archaea, bacteria, and eukaryotes.
Types
The cytoskeletons of eukaryotic cells are of three types: (1) microfilaments, (2) microtubules, and (3) intermediate filaments.
The microfilament (also called actin filament) is a helical polymer of actin sub-units, with diameter of 7 nm. It provides mechanical support for the cell or maintains structural integrity of the cell by forming a band just beneath the cell membrane. It also participates in certain cell junction by linking transmembrane proteins (e.g., cell surface receptors) to cytoplasmic proteins. It also anchors the centrosomes at opposite poles of the cell during mitosis. It particularly aids in the contraction of the cell during cytokinesis. It is also involved in cytoplasmic streaming (i.e. Intracellular movement, or the flowing of cytoplasm within cells). It enables cell locomotion (through lamellipodia, filopodia, or pseudopodia). It could also interact with myosin (“thick”) filaments in skeletal muscle fibers to provide the force of muscular contraction.
The microtubules are cytoplasmic tubules that serve as structural components of cytoskeleton, cilia, and eukaryotic flagella. A microtubule is made up of polymers of alpha- and beta-tubulin dimers. It is a tubular structure with diameter of 25 nm, length ranging from 200 nm to 25 micrometers, and wall thickness of 5 nm. It exhibits polarity and are organized by a microtubule organizing centers (e.g. centrioles and basal bodies). Its functions are associated with providing intracellular shape, locomotion, and transport. For instance, in cellular division, the microtubules are a source of spindle fibers. They give rise to the spindle apparatus that plays an important role in moving and separating chromosomes. There are three main subgroups of microtubules: the polar microtubules (those extending across the cell, as in from centrosome to centrosome), the astral microtubules (those that anchor the spindle poles to the cell membrane), and the kinetochore microtubules (those that extend from the centrosome to the kinetochore protein in the centromere of the chromosome).
The intermediate filaments are polymers comprised of two anti-parallel helices or dimers of varying protein sub-units with diameters ranging from 8 to 12 nm. Examples are vimentin (mesenchyme), glial fibrillary acidic protein (glial cells), neurofilament proteins (neuronal processes), keratins (epithelial cells), and nuclear lamins.
| type of cytoskeleton | Features | Functions |
| Microfilaments | helical polymer of actin sub-units (e.g. actin) | Cell shape Cell locomotion (via filopodia, pseudopodia, or lamellipodia) Intracellular movement or transport Cytokinesis (by aiding centrosomes at opposite poles) Muscle contraction (with myosin filaments) Cytoplasmic streaming |
| Microtubules | tubular structure with a diameter of 25nm and length ranging from 200nm to 25μm; exhibits polarity; in cilia and flagella, 9+2 microtubular arrangement (e.g. alpha-tubulin and beta-tubulin) | Intracellular shape Cell locomotion (as axoneme of cilia and flagella) Intracellular transport of organelles (e.g. mitochondria) via dyneins and kinesins Spindle fiber formation |
| Intermediate filaments | two anti-parallel helices or dimers of varying protein sub-units with diameters ranging from 8 to 12 nm (e.g. vimentin (mesenchyme), glial fibrillary acidic protein (glial cells), neurofilament proteins (neuronal processes), keratins (epithelial cells), and nuclear lamins) | Cell shape (by bearing tension) “Scaffolding” for cell and nucleus Nuclear lamina formation Anchor organelles Cell-cell connections (when with proteins and desmosomes) |
Other eukaryotic cytoskeletons are septin and spectrin. Septins form complexes with each other to create attachment points for other proteins inside the cell. Spectrins are proteins forming a meshwork underl the plasma membrane, potentially restricting the lateral mobility of integral proteins.
In prokaryotic cells, homologous structures were identified. FtsZ was the first to be identified. With TubZ and RepX, FtsZ are the tubulin-like proteins in prokaryotes. MreB and FtsA are the actin-like proteins. Other cytoskeletal types in prokaryotes are MinD, Crescentin, ParM and SopA, MinCDE system, Bactofilin, and Crenactin. Although some of the cytoskeletons in eukaryotes are similar in form and structure with those in the prokaryotes, they basically differ in function. For example, the actin cytoskeleton is involved in cell division in eukaryotes but the tubulin-like cytoskeletons (usually, FtsZ-ring) are involved in the cell division of prokaryotes.
Biological functions
Cytoskeleton is involved in cell shape formation, cell division, cell differentiation, intracellular organization, and cell movement. The cytoskeleton is also involved in cell signaling pathways, e.g. in the uptake of extracellular material during endocytosis.
Supplementary
Etymology
- cyto– (cell) + skeleton
Abbreviation
Derived term(s)
- cytoskeletal (adjective)
Further reading
See also
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