Term
| What are the three types of filaments founds in eukaryotic cells? |
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Definition
1) Microfilaments
2) Intermediate filaments
3) Microtubules |
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Term
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Definition
• Tough, 10 nm diameter rope-like filaments formed by assembly of fibrous intermediate filament proteins.
• Gives the cell tensile strength and helps the cell hold its shape.
• Except for the lamins during the cell cycle, intermediate filaments are not dynamic. |
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Term
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Definition
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Term
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Definition
| False, except for the lamins during the cell cycle. |
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Term
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Definition
• 25 nm diameter tubes formed by assembly of dimers of the proteins alpha and beta tubulin.
• Used as tracks for motility, in particular the movement of vesicles, the segregation of chromosomes at cell division, and the framework for cilia.
• Microtubules are generally very dynamic. |
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Term
| What is the width of microtubules? |
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Definition
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Term
| How are microtubules formed? |
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Definition
By assembly of dimers of the proteins alpha and beta
tubulin. |
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Term
| T or F: Microtubules are generally dynamic? |
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Definition
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Term
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Definition
• 7 nm diameter flexible filaments formed by polymerization of actin, a 42 kd globular protein, stabilized and organized by the binding of actin-associated proteins.
• Used as tracks for motility and frequently associated with the plasma membrane where it plays a critical role in the dynamic organization of the cell cortex-changes in cell shape.
• The actin cytoskeleton is dynamic. |
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Term
| What is the width of actin microfilaments? |
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Definition
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Term
| How are actin filaments formed? |
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Definition
By polymerization of actin, a 42 kd globular
protein, stabilized and organized by the binding of actin-associated proteins. |
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Term
| T or F: Actin microfilaments are dynamic? |
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Definition
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Term
| Intermediate filaments (figure) |
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Definition
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Term
| T or F: Intermediate filaments have a distinct polarity? |
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Definition
| False, and therefore they are ill-suited for a role in motility. |
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Term
| How are intermediate filaments assembled? |
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Definition
| They are assembled from homo- or heterodimers of intermediate filament (IF) proteins via tetrameric intermediates. Assembly requires no cofactors and once formed these filaments are relatively stable (the exception are the lamins). |
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Term
| What are the 4 classes of intermediate filament proteins? |
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Definition
1) Keratins
2) Vimentin and vimentin-related
3) Neurofilaments
4) Nuclear lamins
* 1-3 are cytoplasmic, 4 is in all nucleated cells |
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Term
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Definition
| A class of intermediate filaments |
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Term
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Definition
| Vimentin is widespread in cells of mesodermal origin. |
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Term
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Definition
| IF primarily in muscle cells where it holds together adjacent myofibrils (contractile units). |
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Term
| Glial fibrillary acidic protein (GFA) |
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Definition
| IF in astrocyctes and glial cells, which are supporting cells of the central nervous system (CNS). |
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Term
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Definition
| IF formed from three subunits co-assemble into filaments in neurons that extend along the length of axons, providing these long cellular extensions with tensile strength. |
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Term
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Definition
| IF present as a meshwork on the inner surface of the nuclear membrane of all cells. These are the most dynamic of the IFs-they disassemble at the beginning of mitosis and reassemble at the end of mitosis. Phosphorylation/dephosphorylation regulates this cycle of assembly/disassembly. |
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Term
| What are some structures associated with intermediate filaments? |
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Definition
1. Lamin proteins associate with the inner nuclear membrane to form a structure called the nuclear lamina (note: do not confuse this structure with the extracellular basal lamina). They are important for the assembly of the nuclear membrane around chromatin following mitosis.
2. Some IFs (keratin or desmin filaments) interact with membrane adhesion sites to form desmosomes and hemi-desmosomes. These structures mediate cell-cell attachment and thereby tissue cohesiveness. Desmosomes connect IF in adjacent cells of an epithelial sheet (ECB Fig. 17-2, above). Mutations in either the junctional proteins or the intermediate filament proteins can disrupt the strength of this cell layer. |
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Term
| What is the clinical significance of types of (specifically keratins) intermediate filaments? |
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Definition
• Typing of keratins can be very useful in diagnosis and treatment of epithelial cancers.
• Mutations in human epidermal keratins can cause epidermolysis bullosa, a skin blister
disease. |
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Term
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Definition
| A skin blister disease caused by mutations in human epidermal keratins. |
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Term
| What is the structure of microtubules? |
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Definition
• Microtubules are 25 nm diameter hollow tubes assembled from dimers of alpha and beta tubulin.
• Both alpha and beta tubulin are 55 kd globular proteins that contain GTP binding sites.
• Only beta tubulin can hydrolyze its bound GTP to GDP when it is assembled into a microtubule. Formation of the tubulin dimer protects the GTP on alpha tubulin. |
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Term
| T or F: Both alpha and beta tubulin can hydrolyze its bound GTP to GDP? |
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Definition
False. Only beta tubulin can hydrolyze its bound GTP to GDP when it is assembled into a
microtubule. |
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Term
| Microtubule assembly (figure) |
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Definition
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Term
| What is the process of microtubule assembly? |
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Definition
• In cells, assembly requires GTP, Mg++, and a ‘critical’ subunit concentration.
• Beta tubulin in a microtubule acts as a slow GTPase, and GDP must be exchanged for GTP again before a subunit is re-used for assembling another microtubule.
• End-to-end binding in a head-to-tail orientation results in structural polarity of microtubules, which have plus (fast-growing) and minus (slow-growing) ends.
• Microtubule-associated proteins and drugs can regulate assembly in vitro and in vivo. |
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Term
| What is required of cells for microtubule assembly? |
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Definition
| GTP, Mg2+, and a "critical" subunit concentration. |
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Term
| T or F: Microtubules have a distinct polarity? |
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Definition
| True. End-to-end binding in a head-to-tail orientation results in structural polarity of microtubules, which have plus (fast-growing) and minus (slow-growing) ends. |
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Term
| Plus ends of microtubules |
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Definition
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Term
| Minus ends of microtubules |
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Definition
| Slow growing ends of microtubules. |
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