Cytoskeleton
The cytoskeleton is a network of protein filaments within a cell that provides structural support, helps with cell movement, and facilitates intracellular transport. It is composed of three main types of filaments: microfilaments, intermediate filaments, and microtubules. The cytoskeleton plays a crucial role in maintaining cell shape, organizing cellular components, and enabling cell motility.
7 Key excerpts on "Cytoskeleton"
eBook - ePubCell Biology
A Short Course
- Stephen R. Bolsover, Andrea Townsend-Nicholson, Greg FitzHarris, Elizabeth A. Shephard, Jeremy S. Hyams, Sandip Patel(Authors)
- 2022(Publication Date)
- Wiley-Blackwell(Publisher)
...These core structural components of the Cytoskeleton are accompanied by associated proteins, such as motor proteins that power the movement of cargoes along the filamentous networks. The term “Cytoskeleton” implies a rigid and static frame within the cell, but nothing could be further from the truth. All three filament systems are highly dynamic and able to rapidly alter their organization in response to the needs of the cell at any given moment. MICROTUBULES Microtubules possess a combination of physical properties that allows them to participate in multiple cellular functions. They can form bundles of rigid fibers to make structural scaffolds that serve an important role in the determination of cell shape, and also provide tracks along which the directed movement of other cellular components such as vesicles and organelles can occur. Microtubules have an inherent structural polarity that enables the cell to control the directionality of this transport. Movement can be powered by enzymes called microtubule motors that move cargoes along the microtubule surface, or can occur by modification of the lengths of microtubules themselves. Microtubules can be rapidly formed and broken down, a property that allows the cell to respond to subtle environmental changes. Finally, they play a role in one of the most important and precise of all movements within the cell, the segregation of chromosomes at mitosis and meiosis into newly forming daughter cells (Chapter 14). Microtubules are composed of the protein tubulin, which consists of two subunits designated α and β. These have been highly conserved throughout evolution and the α‐ and β‐ tubulins present in the cells of complex eukaryotes such as humans are much the same as those in a simple eukaryote such as a yeast. In the human genome there are eight α‐tubulin genes and nine of β‐tubulin. α‐tubulin/β‐tubulin dimers assemble into chains called protofilaments, 13 of which make up the microtubule wall (Figure 13.2)...
eBook - ePub- Antoni Horst(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...Chapter 7 THE MOLECULAR STRUCTURES OF THE EUKARYOTIC CELL I. THE Cytoskeleton According to earlier views the cytoplasm of a cell was a formless area in which the nucleus and the other organelles were dispersed. In contrast to this, recent investigations have revealed three kinds of filaments in the cytoplasm that considerably confine the displacement of the particular organelles in cells. The finest filaments are microfilaments, predominantly 6 nm in diameter, composed of the protein called actin. The largest filaments are microtubules, 22 nm in diameter, composed of the protein called tubulin. The third kind of filaments are intermediate filaments, 7 to 11 nm in diameter; the protein content of these filaments varies, dependent on the cell type. All the filaments form a network that stabilizes shape and cell structure, and is termed the Cytoskeleton. The microtubules radiate from the centrosome (also called cytocenter) to the cell membrane. The organization of microtubules changes during mitosis. The chromosomes in the nucleus condense and separate into two sets. Simultaneously, the microtubules degrade and tubulin becomes organized into the mitotic spindle. A network of microtubules extends from the poles of the dividing cell to the chromosome sets and attracts them to the two poles. The intermediate filaments are differently organized in different tissues according to their constituent protein. In the epithelial cells they consist of keratin. Intermediate filaments usually are dispersed in the whole cytoplasm, but in several cells they appear in the form of bundles or individual filaments. In many cells they are combined with microtubules. The basic protein of microfilaments—actin—represents a monomer, known as globular actin, termed G-actin. G-actin is stored in connection with profilin...
eBook - ePubBiotensegrity
The Structural Basis of Life
- Graham Scarr(Author)
- 2019(Publication Date)
- Handspring Publishing Limited(Publisher)
...The inside of the nucleus also has its own skeleton, and this is constructed from comparable microfibers that link the outer Cytoskeleton with the chromosomes and other structural proteins, and is responsible for organizing their functions (Wang et al., 2009; Mammoto et al., 2012). These fibrous molecules are all part of a dynamic structure that is constantly assembling and disassembling its components in response to the mechanical forces exerted on them, and which enables the system to readily adapt to changes in the surrounding environment (Tan et al., 2016). Tension is generated through the action of actomyosin motors (which act like turnbuckles in ‘tightening’ the microfilaments) (Martin & Goldstein, 2014) and polymerization of microtubules (Tolić-Nørrelykke, 2008), and any change in force at one part of the structure causes the entire Cytoskeleton to alter cell shape – a defining characteristic of tensegrity. This fibrous lattice also offers a huge surface area for the attachment of enzymes and their substrates and mediates critical metabolic functions such as glycolysis, messenger RNA transcription, and protein synthesis (Figure 5.5), and its continuity with the nuclear scaffold also ensures its involvement in DNA transcription and replication (Mammoto et al., 2012). Some of the products of these activities are then transported to different parts of the cell by kinesin and dynein motors that ‘walk’ along the microtubules (Tolić-Nørrelykke, 2008). Global changes in cytoskeletal tension and cell shape are thus able to quickly alter cellular biochemistry and switch between different functional states such as growth, differentiation, movement and apoptosis (programmed cell death) (Ingber et al., 2014). Figure 5.5 Schematic showing how tensional forces can be transferred between the internal Cytoskeleton and surrounding extracellular matrix (ECM) and stimulate the activity of enzyme signaling cascades that influence cell function (not to scale)...
eBook - ePub- Thomas D. Pollard, William C. Earnshaw, Jennifer Lippincott-Schwartz, Graham Johnson(Authors)
- 2016(Publication Date)
- Elsevier(Publisher)
...Most microtubules in cells have the same polarity relative to the organizing centers that initiate their growth (eg, the centrosome) (Fig. 1.2). Their rapidly growing ends are oriented toward the periphery of the cell. Individual cytoplasmic microtubules are remarkably dynamic, growing and shrinking on a time scale of minutes. Microtubules serve as mechanical reinforcing rods for the Cytoskeleton and the tracks for two classes of motor proteins that use the energy liberated by ATP hydrolysis to move along the microtubules. Kinesin moves its associated cargo (vesicles and RNA-protein particles) along the microtubule network radiating away from the centrosome, whereas dynein moves its cargo toward the centrosome. Together, they form a two-way transport system that is particularly well developed in the axons and dendrites of nerve cells. Toxins can impair this transport system and cause nerve malfunctions. During mitosis, the cell assembles a mitotic apparatus of highly dynamic microtubules and uses microtubule motor proteins to distribute the replicated chromosomes into the daughter cells. The motile apparatus of cilia and flagella is built from a complex array of stable microtubules that bends when dynein slides the microtubules past each other. A genetic absence of dynein immobilizes these appendages, causing male infertility and lung infections. Microtubules, intermediate filaments, and actin filaments each provide mechanical support for the cell. Interactions of microtubules with intermediate filaments and actin filaments unify the Cytoskeleton into a continuous mechanical structure. These polymers also provide a scaffold for some cellular enzyme systems. Cell Cycle Cells carefully control their growth and division using an integrated regulatory system consisting of protein kinases (enzymes that add phosphate to the side chains of proteins), specific kinase inhibitors, transcription factors, and highly specific protein degradation...
- (Author)
- 2013(Publication Date)
- AP Cell(Publisher)
...We thank all members of the Physics of the Cytoskeleton and Morphogenesis Laboratory for their experimental work and discussions. This work was supported by grants from the Human Frontier Science Programs (RGP0004/2011 to L.B. and RGY0088/2012 to M.T.) and Institut National du Cancer (PLBIO 2011-141 to M.T.). Trends in Cell Biology, Vol. 22, No. 12, December 2012 © 2012 Elsevier Inc. http://dx.doi.org/10.1016/j.tcb.2012.08.012 Summary The Cytoskeleton architecture supports many cellular functions. Cytoskeleton networks form complex intracellular structures that vary during the cell cycle and between different cell types according to their physiological role. These structures do not emerge spontaneously. They result from the interplay between intrinsic self-organization properties and the conditions imposed by spatial boundaries. Along these boundaries, Cytoskeleton filaments are anchored, repulsed, aligned, or reoriented. Such local effects can propagate alterations throughout the network and guide Cytoskeleton assembly over relatively large distances. The experimental manipulation of spatial boundaries using microfabrication methods has revealed the underlying physical processes directing Cytoskeleton self-organization. Here we review, step-by-step, from molecules to tissues, how the rules that govern assembly have been identified. We describe how complementary approaches, all based on controlling geometric conditions, from in vitro reconstruction to in vivo observation, shed new light on these fundamental organizing principles. Setting Boundaries The reproducible shape and spatial organization of organs imply the existence of deterministic rules directing the assembly of complex biological structures. Organ shape depends on cell architecture, which is supported by Cytoskeleton networks. The formation of defined and geometrically controlled intracellular structures relies on the self-organization properties of the Cytoskeleton...
eBook - ePubCell Boundaries
How Membranes and Their Proteins Work
- Stephen White, Gunnar von Heijne, Donald Engelman(Authors)
- 2021(Publication Date)
- Garland Science(Publisher)
...The intracellular distribution of two of these, actin filaments and microtubules, is revealed in Figure 7.4 by means of fluorescently labeled antibodies. Notice that the actin filaments (red) are arranged concentrically around the cell nucleus, whereas the microtubules (green) are arranged radially. The actin filaments determine cell shape and underlie whole-cell locomotion. The microtubules radiate outward from the nucleus, serving as tracks for the orderly movement of vesicles carried by molecular motors from endoplasmic reticulum (ER) to Golgi to plasma membrane. The radial microtubules thus determine the locations of organelles within cells (Figure 7.1). Not shown in the figure are the intermediate filaments that provide mechanical strength. As in RBCs, the plasma membrane in eukaryotic cells is attached to the underlying Cytoskeleton and consequently, responds to dynamic changes of the Cytoskeleton. Unlike in RBCs, the Cytoskeleton not only serves to control the shape of the cell but can be rapidly disassembled and reassembled during the cell cycle and in response to various internal and external stimuli; this is further discussed in Chapter 15. The general properties of actin, microtubules, and intermediate filaments are summarized in Box 7.1. Figure 7.4 The Cytoskeleton of a eukaryotic cell. Microtubules are in green and actin filaments in red. The nucleus is in blue. The cell in this picture has been fixed, and the microtubules and actin filaments have then been visualized using fluorescent antibodies that bind specifically to each kind of structure. Notice that microtubules are generally arranged radially with respect to the nucleus, while actin is arranged circumferentially. (From Alberts B, Johnson A, Lewis JH et al. [2007] Molecular Biology of the Cell, 5th Edition. Garland Science, New York. With permission from W. W...
eBook - ePubThe Avian Erythrocyte
Its Phylogenetic Odyssey
- Chester A. Glomski, Alessandra Pica(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
...It lines and interfaces with the inner surface of the entire plasmalemma and also thereby envelops the nucleus. The membrane skeleton, particularly its spectrin component, is believed to be largely responsible for the elasticity of the inframammalian (and mammalian) erythrocytic membrane. Further, the MS is thought to be held in a partly extended state by interacting with the plasmalemma and can be viewed as an elastic molecular fabric with a memory for a flattened elliptical cell shape (Cohen 1991). The intermediate filaments of the erythrocyte’s Cytoskeleton connect the nucleus with the membrane skeleton and the plasma membrane; in regions where the nucleus is absent, these filaments link opposing cytoplasmic faces of the membrane skeleton (Figure 9). They are characterized by their ten-nanometer diameter and their membership in the class of filamentous cytoplasmic proteins that have vimentin as the major constituent. (Note: Five chemically distinct classes of intermediate filaments have been identified in eukaryotic cells. Each class is chemically distinct and is characteristic of a particular cell type. For example, keratin filaments are found in epithelial cells while vimentin is seen primarily in mesenchymal cells and cells of mesenchymal origin [Lazarides 1980].) The occurrence of cytoplasmic filaments in turkey and chicken erythrocytes which extend from the nucleus to the cytoplasmic membrane was suggested by Harris and Brown (1971) and specifically identified by Virtanen et al. (1979) in red cells from one-day-old chickens. They were visualized in both instances under transmission electron microscopy in lysed red cells. It was initially proposed that intermediate filaments might have a role in the anchoring or positioning of the nucleus (Harris and Brown 1971, Virtanen et al. 1979, Lazarides 1980)...
