Term
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Definition
| Hollow tubes of proteins that can rapidly disassemble and reassemble. They are 20-25 nm in diameter. They are composed of dimeric tubulin molecules, each containing an α-tubulin molecule and a β-tubulin molecule. All dimers have the same orientation. The minus (nongrowing) end corresponds to α-tubulin while the plus (growing) end corresponds to β-tubulin |
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Term
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Definition
| microtubule-organizing center (MTOC or centrosome) is the region of the cell containing centrioles and pericentriolar material. It is the region where most microtubules are formed and from which they are directed to specific destinations within the cell. The minus end remains attached to the MTOC and the plus end moves away from MTOC |
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Term
| Role of GTP in MT polymerization |
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Definition
| In polymerization of tubulin dimmers, each tubulin molecule binds GTP in the presence of Mg2+. The GTP-tubulin complex is then polymerized, and at some point GTP is hydrolyzed to GDP. |
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Term
| dynamic instability of MTs |
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Definition
| The cytoplasm contains a pool of free tubulin dimers, which is in equilibrium with polymerized tubulin. Equilibrium is shifted towards depolymerization by exposure to low temperatures or high pressure. Dynamic instability of microtubules refers to the pattern of microtubule assembly and disassembly. MT’s are fired from the MTOC toward the cell periphery and are subsequently retracted. |
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Term
| Microtubule Associated Proteins (MAPs) |
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Definition
| modify the speed of polymerization or depolymerization and anchor MT’s to specific organelles. They also causes non-depolymerizing microtubules, such as in cilia and flagella |
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Term
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Definition
| provide a network for movement of organelles within the cell and chromosomes during cell division. They are also involved in vesicular transport, movement of cilia and flagella, mitotic spindles, cell elongation, movement and shape. |
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Term
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Definition
| Use ATP hydrolysis to move vesicles toward the minus end of MT and can transport toward the MTOC. In mitosis, dyneins move the chromosomes along the MT’s of the mitotic spindle. |
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Term
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Definition
| Use ATP hydrolysis to move towards the plus end of MT's and can transport away from the MTOC. In mitosis, they reduce the overlap between MT’s from the two spindle poles, pushing the two spindle poles apart toward each daughter cell. |
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Term
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Definition
| Kartagener’s syndrome is caused by defects in the organization of MT’s and MAPs. This immobilizes the cilia of respiratory epithelium, interfering with the ability of the respiratory system to clear accumulated secretions. Other clinical features can include dysfunction of MT’s, male sterility due to decreased sperm motility, and infertility in women due to impaired cicliary transport of the ovum through the oviduct. |
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Term
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Definition
| binds to tubulin molecules and prevents their polymerization. It is used to treat acute attacks of gout to prevent neutrophil igration, and to lower their ability to respond to urate crystal deposits in the tissues |
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Term
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Definition
| Vinblastine binds to MT’s and inhibits the formation of the mitotic spindle essential for cell division. It is used as antimitotic and antiproliferative agents in cancer therapy |
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Term
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Definition
| Taxol is used in chemotherapy for breast cancer because it prevents MT depolymization by stabilizing the MT’s, arresting cancer cells in various stages of cell division. |
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Term
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Definition
| Microfilaments (or actin filaments) are linear helical arrays 6-8 nm in diameter of polyermized actin molecules. They are thinner, shorter and more flexible than MT’s. The fast-growing end is the plus (barbed) end while the slow-growing end is the minus (pointed) end. |
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Term
| Equilibrium between G-actin and F-actin and role of ATP |
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Definition
| G-actin (globular actin) are free actin molecules in the cytoplasm. F-actin (filamentous actin) is polymerized actin of the filament. Actin polymerization requires K+, Mg2+, and ATP, which is hydrolyzed to ADP after each G-atin molecule is incorporated into the filament. Rate of polymerization depends on the local concentration of G-actin and the interaction of actin-binding proteins (ABPs), which can prevent or enhance polymerization. |
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Term
| Actin Binding Proteins (ABPs) |
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Definition
| ABPs can prevent or enhance actin polymerization. They are also responsible for the filaments’ organization |
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Term
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Definition
| These cross-link actin filaments into parallel arrays, creating actin filament bundles. For example, fimbrin cross-links actin filaments in microvilli to provide support and imparts rigidity |
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Term
| actin-filament severing proteins |
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Definition
| These cut long actin filaments into short fragments. For example, gelsolin normally initiates actin polymerization but at high Ca2+ concentrations causes severing of the actin filaments, converting an actin gel into a fluid state. |
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Term
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Definition
| These block further addition of actin molecules by binding to the free end of an actin filament |
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Term
| actin cross-linking proteins |
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Definition
| These cross-link actin filaments with each other |
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Term
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Definition
| Actin motor proteins are members of the myosin family that hydrolyze ATP to provide energy for movement along the actin filament from the minus end ot the plus end. |
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Term
| functions of actin filaments |
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Definition
| tight junctions, core of microvilli and terminal web, cell locomotion (lamellipodia), cell processes (filopodia) |
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Term
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Definition
| leading-edge extensions of a crawling cell and contain elongated bundles of actin filaments with their plus ends directed toward the plasma membrane. |
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Term
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Definition
| small protrusions located around the cell surface. They contain loose aggregates of 10 to 20 actin filaments organized in the same direction with their plus ends directed toward the plasma membrane |
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Term
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Definition
| prevent actin polymerization by binding to the plus end of the actin filament, inhibiting lymphocyte migration, phagocytosis and cytokinesis |
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Term
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Definition
| binds to and stabilizes actin filaments, preventing their depolymerization. It disrupts the equilibrium between F-actin and G-actin, leading to cell death. |
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Term
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Definition
| Intermediate filaments are ropelike and are important for cell structure. They have a diameter of 8 to 10 nm, in between that of actin filaments and microtubules. The subunits of IF’s have considerable variability. They also do not typically disappear and re-form. IF proteins have a highly variable central rod-shaped domain with strictly conserved globular domains at each end. If’s are assembled from a pair of helical monomers that twist around each other ot form coiled-coil dimmers. These then twist around each other in an antiparallel fashion to form a staggered tetramer. These tetramers, each an individual unit, is aligned along the axis of the filament. The IF has no polarity. |
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Term
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Definition
| Keratins only assemble as heteropolymers, as an acid cytokeratin and a basic cytokeratin molecule form a dimer. Each keratin pair is characteristic of a particular type of epithelium. Hard keratins are found in skin appendages, such as hair and nails. Keratin filaments span the cytoplasm of epithelial cells and, via desmosomes, connect with keratin filaments in neighboring cells. |
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Term
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Definition
| Vimentin is the most abundant IF found in mesoderm-derived cells, including fibroblasts |
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Term
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Definition
| Desmin is characteristic of muscle cells |
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Term
| Glial fibrillar acidic protein (GFAP) |
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Definition
| GFAP is found in glial cells (highly specific for astrocytes) |
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Term
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Definition
| Peripherin is found in many peripheral nerve cells |
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Term
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Definition
| Neurofilaments are IF proteins that are mostly expressed in the axons of nerve cells |
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Term
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Definition
| Lamins, specifically nuclear lamins, form a network-like structure that is associated with the nuclear envelope. Lamins are located within the nucleoplasm of almost all differentiated cells in the body |
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Term
| intermediate filament associated proteins (IFAPs) |
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Definition
| Intermediate filament associated proteins (IFAPs) function within the cytoskeleton as integral parts of the molecular architecture of cells |
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Term
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Definition
| IFAPs that form the attachment plaques for intermediate filaments in desmosomes and hemidesmosomes. The i/a of IF’s with cell-to-cell and cell-to-extracellualr matrix junctions provides mechanical strength and resistance to extracellular forces |
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Term
| Neurofibrillary tangles in Alzheimer's disease |
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Definition
| The neurofibrillary tangles contain neurofilaments and other microtubule-associated proteins. They occur because of improper assembly of IF’s. |
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Term
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Definition
| Centrioles are paired, short, rodlike cytoplasmic cylinders built from nine MT triplets. They are found near the nucleus in the MTOC. In resting cells, centrioles have an orthogonal orientation (one centriole in the pair is arrayed at a right angle to the other). |
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Term
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Definition
| around each individual centriole in a starlike fashion. They establish the axis of the developing mitotic spindle |
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Term
| how abnormal centrioles play a role in cancer formation and progression |
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Definition
| Alterations of mechanisms regulating centriole duplication may lead to multiplication and abnormalities of centrioles. They can distort the mitotic spindle, leading to abnormal sorting of chromosomes during cell divisions. The resulting aneuploidy may increase the activity of oncogenes or decrease protection from tumor-suppressor genes. |
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Term
| what are basal bodies derived from? |
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Definition
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Term
| difference between spindle MTs and kinetochore MTs |
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Definition
| Spindle MTs are involved in spindle integrity and elongation. Kinetochore MTs are involved in chromosome separation |
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