Κυτταροσκελετός Πολύπλοκο δίκτυο πρωτεϊνικών ινιδίων που εκτείνεται σε όλο το κυτταρόπλασμα Δίνει την ικανότητα στα ευκαρυωτικά κύτταρα να: οργανώνουν τα πολυάριθμα συστατικά τους προσλαμβάνουν ποικίλα σχήματα πραγματοποιούν συγχρονισμένες κινήσεις Στήριξη «οστά» Κίνηση «μύες» Ενδοκυττάριες κινήσεις: μεταφορά οργανιδίων μοίρασμα χρωμοσωμάτων διαχωρισμός θυγατρικών κυττάρων Z. Βενέτη, Βιολογία Α

Τα τρία είδη των πρωτεϊνικών ινιδίων που σχηματίζουν τον κυτταροσκελετό Z. Βενέτη, Βιολογία Α

Δίκτυο ενδιάμεσων ινιδίων Keratin filaments in epithelial cells. Immunofluorescence micrograph of the network of keratin filaments (green) in a sheet of epithelial cells in culture. The filaments in each cell are indirectly connected to those of its neighbors by desmosomes (discussed in Chapter 19). A second protein (blue) has been stained to reveal the location of the cell boundaries. (Courtesy of Kathleen Green and Evangeline Amargo.) Figure 16-19. Blistering of the skin caused by a mutant keratin gene. A mutant gene encoding a truncated keratin protein (lacking both the N- and C-terminal domains) was expressed in a transgenic mouse. The defective protein assembles with the normal keratins and thereby disrupts the keratin filament network in the basal cells of the skin. Light micrographs of cross sections of normal (A) and mutant (B) skin show that the blistering results from the rupturing of cells in the basal layer of the mutant epidermis (small red arrows). (C) A sketch of three cells in the basal layer of the mutant epidermis, as observed by electron microscopy. As indicated by the red arrow, the cells rupture between the nucleus and the hemidesmosomes (discussed in Chapter 19), which connect the keratin filaments to the underlying basal lamina. (From P.A. Coulombe et al., J. Cell Biol. 115:1661–1674, 1991. © The Rockefeller University Press.) Z. Βενέτη, Βιολογία Α

Figure 16-13. The domain organization of intermediate filament protein monomers. Most intermediate filament proteins share a similar rod domain that is usually about 310 amino acids long and forms an extended a helix. The amino-terminal and carboxyl-terminal domains are non-a-helical and vary greatly in size and sequence in different intermediate filaments. Z. Βενέτη, Βιολογία Α

Η κατασκευή ενός ενδιάμεσου ινιδίου Z. Βενέτη, Βιολογία Α

Τα ενδιάμεσα ινίδια προσδίδουν στα κύτταρα μηχανική ισχύ Figure 16-20. Two types of intermediate filaments in cells of the nervous system. (A) Freeze-etch electron microscopic image of neurofilaments in a nerve cell axon, showing the extensive cross-linking through protein cross-bridges—an arrangement believed to give this long cell process great tensile strength. The cross-bridges are formed by the long, nonhelical extensions at the C-terminus of the largest neurofilament protein (NF-H). (B) Freeze-etch image of glial filaments in glial cells, showing that these intermediate filaments are smooth and have few cross-bridges. (C) Conventional electron micrograph of a cross section of an axon showing the regular side-to-side spacing of the neurofilaments, which greatly outnumber the microtubules. (A and B, courtesy of Nobutaka Hirokawa; C, courtesy of John Hopkins.) Z. Βενέτη, Βιολογία Α

Οι κύριες κατηγορίες ενδιάμεσων ινιδίων Z. Βενέτη, Βιολογία Α

Figure 16-20. Mechanical properties of actin, tubulin, and vimentin polymers. Networks composed of either microtubules or actin filaments or vimentin filaments, all at equal concentration, were exposed to a shear force in a viscometer and the resulting degree of stretch measured. The results show that microtubule networks are easily deformed but that they rupture (indicated by red starburst) and begin to flow without limit when stretched beyond 50% of their original length. Actin filament networks are much more rigid, but they also rupture easily. Vimentin networks, by contrast, are easily deformed, but unlike microtubule networks, they withstand large stresses and strains without rupture. Vimentin filaments are therefore well suited to maintain cell integrity. Z. Βενέτη, Βιολογία Α

Η πλεκτίνη συμβάλλει στο σχηματισμό δεσμίδων από ενδιάμεσα ινίδια και συνδέει αυτά τα ινίδια με άλλα δίκτυα πρωτεϊνών του κυτταροσκελετού Z. Βενέτη, Βιολογία Α

Τα ενδιάμεσα ινίδια που βρίσκονται κάτω από την πυρηνική μεμβράνη Z. Βενέτη, Βιολογία Α

ΜΙΚΡΟΣΩΛΗΝΙΣΚΟΙ Z. Βενέτη, Βιολογία Α

Οργάνωση των μικροσωληνίσκων στο εσωτερικού του κυττάρου Figure 11.39. Intracellular organization of microtubules The minus ends of microtubules are anchored in the centrosome. In interphase cells, the centrosome is located near the nucleus and microtubules extend outward to the cell periphery. During mitosis, duplicated centrosomes separate and microtubules reorganize to form the mitotic spindle. Z. Βενέτη, Βιολογία Α

Οι μικροσωληνίσκοι είναι κοίλοι σωλήνες από τουμπουλίνη Z. Βενέτη, Βιολογία Α

Πολυμερισμός της τουμπουλίνης σε ένα κεντροσωμάτιο Figure 16-3. A centrosome with attached microtubules. As indicated, the slow-growing minus end of each microtubule is embedded in the centrosomematrix ( light green) that surrounds a pair of structures called centrioles. By nucleating the growth of new microtubules, this matrix helps to determine the number of microtubules in a cell. Z. Βενέτη, Βιολογία Α

ΔΥΝΑΜΙΚΗ ΑΣΤΑΘΕΙΑ---οι ΜΣ αυξάνονται και συρρικνούνται διαρκώς Figure 16-4. Growth and shrinkage in a microtubule array. The array of microtubules anchored in a centrosome is continually changing, as new microtubules grow ( red arrows) and old microtubules shrink ( blue arrows). ΔΥΝΑΜΙΚΗ ΑΣΤΑΘΕΙΑ---οι ΜΣ αυξάνονται και συρρικνούνται διαρκώς Z. Βενέτη, Βιολογία Α

Δυναμική αστάθεια στην ανάπτυξη των μικροσωληνίσκων Τα διμερή τουμπ. Με GTP συνδέονται πιο ισχυρά μεταξύ τους από αυτά με GDP, επομένως αυξάνουν. Όμως μπορούν να υδρολύσουν το GTP πριν προλάβουν να προσθέσουν νέες υπομονάδες και τότε τα GTP κάλυμμα χάνεται. Οι GDP υπομονάδες προσδένονται λιγότερο ισχυρά μεταξύ τους στο πολυμερές και απελευθερώνονται εύκολα από το ελεύθερο άκρο. Έτσι ο μικροσωληνίσκος συρρικνούται συνεχώς Figure 16-11. Dynamic instability due to the structural differences between a growing and a shrinking microtubule end. (A) If the free tubulin concentration in solution is between the critical values indicated in Figure 16-9, a single microtubule end may undergo transitions between a growing state and a shrinking state. A growing microtubule has GTP-containing subunits at its end, forming a GTP cap. If nucleotide hydrolysis proceeds more rapidly than subunit addition, the cap is lost and the microtubule begins to shrink, an event called a “catastrophe.” But GTP-containing subunits may still add to the shrinking end, and if enough add to form a new cap, then microtubule growth resumes, an event called “rescue.” (B) Model for the structural consequences of GTP hydrolysis in the microtubule lattice. The addition of GTP-containing tubulin subunits to the end of a protofilament causes the end to grow in a linear conformation that can readily pack into the cylindrical wall of the microtubule. Hydrolysis of GTP after assembly changes the conformation of the subunits and tends to force the protofilament into a curved shape that is less able to pack into the microtubule wall. (C) In an intact microtubule, protofilaments made from GDP-containing subunits are forced into a linear conformation by the many lateral bonds within the microtubule wall, given a stable cap of GTP-containing subunits. Loss of the GTP cap, however, allows the GDP-containing protofilaments to relax into their more curved conformation. This leads to a progressive disruption of the microtubule. Above the drawings of a growing and a shrinking microtubule, electron micrographs show actual microtubules in each of these two states, as observed in preparations in vitreous ice. Note particularly the curling, disintegrating GDP-containing protofilaments at the end of the shrinking microtubule. (C, courtesy of E.M. Mandelkow, E. Mandelkow and R.A. Milligan, J. Cell Biol. 114:977–991, 1991. © The Rockefeller University Press.) Z. Βενέτη, Βιολογία Α

Δυναμική αστάθεια σε ένα ζωντανό κύτταρο Figure 16-12. Direct observation of the dynamic instability of microtubules in a living cell. Microtubules in a newt lung epithelial cell were observed after the cell was injected with a small amount of rhodamine labeled tubulin, as in Figure 16-10. The dynamic instability of microtubules at the edge of the cell can be readily observed. Four individual microtubules are highlighted for clarity; each of these shows alternating shrinkage and growth. (Courtesy of Wendy C. Salmon and Clare Waterman-Storer.) Z. Βενέτη, Βιολογία Α

Φάρμακα που επηρεάζουν την ανάπτυξη των μικροσωληνίσκων Figure 16-21. Effect of the drug taxol on microtubule organization. (A) Molecular structure of taxol. Recently, organic chemists have succeeded in synthesizing this complex molecule, which is widely used for cancer treatment. (B) Immunofluorescence micrograph showing the microtubule organization in a liver epithelial cell before the addition of taxol. (C) Microtubule organization in the same type of cell after taxol treatment. Note the thick circumferential bundles of microtubules around the periphery of the cell. (D) A Pacific yew tree, the natural source of taxol. (B, C from N.A. Gloushankova et al., Proc. Natl. Acad. Sci. USA 91:8597–8601, 1994. © National Academy of Sciences; D, courtesy of A.K. Mitchell 2001. © Her Majesty the Queen in Right of Canada, Canadian Forest Service.) Z. Βενέτη, Βιολογία Α

Οργάνωση μικροσωληνίσκων σε ινοβλάστες και νευρώνες Figure 16-98. Microtubule organization in fibroblasts and neurons. (A) In a fibroblast, microtubules emanate outward from the centrosome in the middle of the cell. Vesicles with plus-end-directed kinesin attached move outward, and vesicles with minus-end-directed dynein attached move inward. (B) In a neuron, microtubule organization is more complex. In the axon, all microtubules share the same polarity, with the plus ends pointing outward toward the axon terminus. No one microtubule stretches the entire length of the axon; instead, short overlapping segments of parallel microtubules make the tracks for fast axonal transport. In dendrites, the microtubules are of mixed polarity, with some plus ends pointing outward and some pointing inward. Z. Βενέτη, Βιολογία Α

Κινητήριες πρωτεΐνες των μικροσωληνίσκων Figure 11.45. Microtubule motor proteins Kinesin and dynein move in opposite directions along microtubules, toward the plus and minus ends, respectively. Kinesin consists of two heavy chains, wound around each other in a coiled-coil structure, and two light chains. The globular head domains of the heavy chains bind microtubules and are the motor domains of the molecule. Dynein consists of two or three heavy chains (two are shown here) in association with multiple light and intermediate chains. The globular head domains of the heavy chains are the motor domains. Z. Βενέτη, Βιολογία Α

Μεταφορά κυστιδίων με μικροσωληνίσκους Figure 11.46. Transport of vesicles along microtubules Kinesin and other plus end-directed members of the kinesin family transport vesicles and organelles in the direction of microtubule plus ends, which extend toward the cell periphery. In contrast, dynein and minus end-directed members of the kinesin family carry their cargo in the direction of microtubule minus ends, which are anchored in the center of the cell. Z. Βενέτη, Βιολογία Α

Η κινητήρια πρωτεΐνη δυνεΐνη συνδεδεμένη σε ένα μεμβρανικό οργανίδιο Figure 16-63. A model for the attachment of dynein to a membrane-enclosed organelle. Dynein requires the presence of a large number of accessory proteins to associate with membrane-enclosed organelles. Dynactin is a large complex (red) that includes components that bind weakly to microtubules, components that bind to dynein itself, and components that form a small actinlike filament made of the actin-related protein Arp1. It is thought that the Arp1 filament may mediate attachment of this large complex to membrane-enclosed organelles through a network of spectrin and ankyrin, similar to the membrane-associated cytoskeleton of the red blood cell (see Figure 10-31). Z. Βενέτη, Βιολογία Α

Figure 16-7. The motor proteins that move along microtubules Figure 16-7. The motor proteins that move along microtubules. Kinesins move toward the plus end of a microtubule, whereas dyneins move toward the minus end. As indicated, both types of microtubule motor proteins exist in many forms, each of which is thought to transport a different cargo Z. Βενέτη, Βιολογία Α

Κροσσοί Z. Βενέτη, Βιολογία Α

Μαστίγια Z. Βενέτη, Βιολογία Α

Η κίνηση ενός μαστιγίου και ενός κροσσού Figure 16-76. The contrasting motions of flagella and cilia. (A) The wave-like motion of the flagellum of a sperm cell from a tunicate. The cell was photographed with stroboscopic illumination at 400 flashes per second. Note that waves of constant amplitude move continuously from the base to the tip of the flagellum. (B) The beat of a cilium, which resembles the breast stroke in swimming. A fast power stroke (red arrows), in which fluid is driven over the surface of the cell, is followed by a slow recovery stroke. Each cycle typically requires 0.1–0.2 sec and generates a force perpendicular to the axis of the axoneme. (A, courtesy of C.J. Brokaw.) Z. Βενέτη, Βιολογία Α

Η διάταξη των μικροσωληνίσκων σε έναν κροσσό ή ένα μαστίγιο Z. Βενέτη, Βιολογία Α

Η κίνηση της δυνεΐνης προκαλεί την κάμψη του μαστιγίου Z. Βενέτη, Βιολογία Α

Νημάτια ακτίνης Κίνηση Μυϊκή συστολή Μικρολάχνες Δέσμες συστολής Προεξοχές ελασματοπόδια νηματοπόδια Συσταλτικός δακτύλιος Z. Βενέτη, Βιολογία Α

Ινίδια ακτίνης

Η υδρόλυση του ΑΤP κατά τον πολυμερισμό της ακτίνης

Πρωτεΐνες που συνδέονται με ακτίνη

Κυτταρικός φλοιός Figure 10-31. The spectrin-based cytoskeleton on the cytosolic side of the human red blood cell membrane. The structure is shown (A) schematically and (B) in an electron micrograph. The arrangement shown in the drawing has been deduced mainly from studies on the interactions of purified proteins in vitro. Spectrin dimers are linked together into a netlike meshwork by junctional complexes (enlarged in the box on the left) composed of short actin filaments (containing 13 actin monomers), band 4.1, adducin, and a tropomyosin molecule that probably determines the length of the actin filaments. The cytoskeleton is linked to the membrane by the indirect binding of spectrin tetramers to some band 3 proteins via ankyrin molecules, as well as by the binding of band 4.1 proteins to both band 3 and glycophorin (not shown). The electron micrograph shows the cytoskeleton on the cytosolic side of a red blood cell membrane after fixation and negative staining. The spectrin meshwork has been purposely stretched out to allow the details of its structure to be seen. In a normal cell, the meshwork shown would be much more crowded and occupy only about one-tenth of this area. (B, courtesy of T. Byers and D. Branton, Proc. Natl. Acad. Sci. USA 82:6153–6157, 1985. © National Academy of Sciences.) Z. Βενέτη, Βιολογία Α

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