Cell Phys Chap 16
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| cytoskeleton | spatially organizes the cytoplasm of eucaryotic cells. Network of protein filaments
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| cytoskeletal filaments | form helical assembleis of subunits that self-associate using combination of end-to-end and side-to-side protein contacts.
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| mechanical properties of cytoskeletal filaments | differences in the structure of the subunits and manner of their self-assembly
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| 3 main cytoskeletal filaments that are fundamental to spatial organization | actin, microtubules, and intermediate filaments
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| are the cytoskeletal filaments effective on their own? | no
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| cytoskeletal filaments usefulness to the cell depends on... | a large number of accessory proteins that link the filaments to other cell components, as well as each other.
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| why are accessory proteins essential in cytoskeletal filaments | essential for the controlled assembly of the cytoskeletal filaments in particular locations, including the motor proteins that either move organelles along the filaments of move the filaments themselves
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| function of actin filaments | determine the shape of the cell's surface and are necessary for whole-cell locomotion
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| function of intermediate filaments | provide mechanical strength and resistance to shear stress
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| function of microtubules | determine the positions of membrane-enclosed organelles and direct intracellular transport
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| long, hollow cylinders made of tubulin subunits; outer diameter of 25 nm | microtubules
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| strong, hollow tubes; more rigid than actin filaments | microtubules
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| microtubules are long and straight, typically with one end attached to a single microtubule-organizing center (MTOC) called a ____________ | centrosome
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| What are the three principal types of cytoskeleton filaments? | microtubules, actin filaments, and intermediate filaments
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| two-stranded helical polymers of actin protein subuinits | actin filaments (microfilaments)
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| appear as flexible structures but are easy to break | actin filaments (microfilaments)
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| organized into linear bundles, 2-D networks, and 3-D gels | actin filaments (microfilaments)
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| diameter of 5-9 nm; thinnest of the three filaments | actin filaments (microfilaments)
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| dispersed throughout the cell, but most highly concentrated in the cortex, just beneath the plasma membrane | actin filaments (microfilaments)
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| rope-like fibers with diameter around 10 nm; | intermediate filaments made of intermediate filament proteins (easy to bend but hard to break)
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| one type of intermediate filament forms a meshwork called the ________ ________ just beneath the inner nuclear membrane | nuclear lamina
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| other types of this cytoskeleton filament extend across the cytoplasm gining cells mechanical strength | intermediate filaments
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| in epithelial tissue, they span the cytoplasm from one cell junction to another, strengthening the entire epithelium | intermediate filaments
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| a _______ _______ is stabilized by multiple contacts between adjacent subunits | helical polymer
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| addition of a third actin monomer to form a ______ makes the entire group more stable | trimer which actss a a nucleus for polymerization
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| for ______ nucleation tthe nucleus is larger and has a more complicated structure consisting of a ring of 13 or more molecules | tubulin
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| this type of molecule binds relatively weakly in nucleation | actin
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| what are the phases of polymerization | assembly of a nucleus (slow "lag phase"), "growth phase" from addition of monomers to nucleus (elongation), and a "steady state" or "equilibrium" when growth and shrinkage of polymer is balanced
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| actin filaments and microtubules assemble (__________) and disassembly by the addition and removal of subunits (_______) at the end of the polymer | (polymerize); (monomers)
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| the rate of addition of monomers is given by the rate constant ______ which has units of _______ | Kon; M-1 sec-1
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| the rate of loss is given by ____ which has units of ____ | Koff; sec-1
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| what is the critical concentration | the number of monomers that add to the polymer per second is proportional to the concentration of the free subunit (konC)
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| As the polymer grows, subunits are used up, and C is observed to _____ until it reaches a constant value called the _____ _____ | drop; critical concentration
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| Does the subunits leaving the polymer end at a constant rate depend on C (koff)? | no
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| the two ends of an actin filament or microtubule polymerize at different rates | true
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| the plus end is the slow-growing end | false
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| the difference in rates of growth at the two ends of an actin filament is made possible by changes in the ________ of each subunit as it enters the polymer. The ________ change affects the rates at which subunits add to the two ends. | conformation; conformation
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| the ratio kon/koff and Cc must be the same at both ends for a simple polymerization reaction (no ATP or GTP hydrolysis). | true
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| Different subunit inretactions are broken when a subunit is lost at either end | false (exactly the same subunit)
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| the final stat of the subunit after dissociation is identical | true
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| Delta G for the subunit loss is different at both ends and determines the equilibrium constant for its association with the end | false (loss is identical)
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| the _______ _______ _______ that accompanies polymerization removes the constraint that keeps then ends growing and shrinking at an identical rate | nucleotide phosphate hydrolysis
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| eacg actin molecule carries a tightly bound ____ that is ydrolyzed to ___ soon after assembly into the polymer | ATP; ADP
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| each tubulin molecule carries a tightly bound ___ that is hydrolyzed to ___ | GTP;GDP
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| ________ of the bound nucleotide reduces the binding affinity of the subunit for neighboring subunits making it more likely to dissociate from each end of the filament | hydrolysis
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| usually the ______ form of nucleotide adds to the filament and the ______ form leaves | triphosphate; diphosphate
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| ATP or GTP that is hydrolyzed must be replenished by a _____ _____ _____ of the free subunit creating a steady state. diphosphate --> triphosphate | nucleotide exchange reaction
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| _____ and _____ bind and hydrolyze nucleoside triphosphates | tubulin and actin
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| tubulin binds ___ | GTP
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| actin binds ___ | ATP
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| what are the two behaviors associated with nucleoside triphosphate hydrolysis observed in cytoskeletal polymers? | dynamic instability and treadmilling
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| dynamic instability predominates in _______ | microtubules
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| ________ predominates in actin filaments | treadmilling
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| what is treadmilling? | a filament assembles at one end while siultaneously disassembling at the other end
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| Microtubules depolymerize about 100 times faster from an end containing ____ tubulin that from one containing ____ tubulin | GDP; GTP
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| A GTP cap favors growth, but if it is lost, then ________ ensues | depolymerization
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| what is dynamic instability | when individual microtubules alternate between a period of slow growth and a period of rapid dissassembly
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| At the apical (upper) surface, facing the intestinal lumen, bundled actin filaments form ______ that increase the cell surface area available for absorbing nutrients from food | microvilli
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| just below the microvilli, a circumferential band of actin filaments contributes to forming _______ _________ that prevent the contents of the intestinal lumen from leaking into the body. | cell-cell junctions
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| ____________ run vertically from the top of the cell to the bottom, and provide a global coordinate system that enables the cell to direct newly synthesized components to their proper locations | microtubules
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| _________ __________ are anchored to other kinds of adhesive structures including desmosomes and ____________ that connect the epithelial cells into a sturdy sheet and attach them to the underlying extracellular matrix on the basal side of the cell. | intermediate filaments; hemidesmosomes
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| the formation of ______ _______ from much smaller protein subunits allows regulated filament assembly and disassembly to reshape the cytoskeleton | protein filaments
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| how is polymerization begun? | by raising the salt concentration in a solution of pure actin subunits or with preformed fragments of actin filaments present to act as nuclei for filament growth.
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| what are the tissue-specific forrms of intermediat filaments found in the cytoplasm of animal cells? | keratin filaments in epithelial cells, neurofilaments in nerve cells, and desmin filaments in muscle cells.
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| what is the primary function of intermediate filaments? | to provide mechanical strength
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| phalloidin | actin-specific drug that binds and stabilizes filaments
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| cytochalasin | actin-specific drug that caps filaments plus ends
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| swinholide | actin-specific drug that severs filaments
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| latrunulin | actin-specific drug that binds subunits and prevents their polymerization
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| taxon | microtubule-specific drug that binds and stabilizes microtubules
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| what are the microtubule-specific drugs that binds subunits and prevents their polymerization? | colchicine, colcemide; vinblastine, vincristine; and nocodazole
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| Bacterial cells also contain homologs of tuulin, actin and intermediate filaments which function to... | form dynamic filamentous structures, determine cell shape, and function in cell division
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| the varied forms and functions of sytoskeletal filament structues in eucaryotic cells depend of a versatile repertoire of ____ _____ | accessory proteins
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| a primary determinant of the sites of cytoskeletal structures is the regulation of the processes that initiate the ___________ of new filaments | nucleation
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| in most animal cells ________ are nucleated at the centrosome, a complex assembly located near the center of the cell | microtubules
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| most actin filaments are nucleated near the ____ ______ | plasma membrane
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| the kinetics of filament assembly and disassembly can be slowed or accelerated by ______ _____ that bind to free subunits or the filaments themselves | accessory proteins
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| some accessory proteins alter filament dynamics by _____ to the ends of filaments or _____ the filaments into smaller fragments | binding; severing
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| some ________ ______ assemble filaments into larger ordered structures by cross-linking them to one another in geometrically defined ways | accessory proteins
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| what happens when the concentration of subunits is less than critical concentration? | both ends shrink
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| ______ rearranges cytoskeltal elements to pursue target | chemotaxis
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| what is formin | actin subunit that nucleates assembly and remains associated with the growing plus end
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| what is ARP complex | actin subunit that nucleates assembly to form a web and remains associated with the minus end
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| actin filament bundling, cross linking, and attachment to membranes creates... | fimbrin and alpha-actin
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| this microtubule filament nucleates assembly and remains associated with the minus ends | gamma-TuRC
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| microtubule filament that stabilizes tubules by binding along sides | MAPs
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| microtubule filament that stabilizes plus ends and accelerates assembly | XMAP215
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| What are the two types of actin filament bundles and what are they composed of? | 1. contractile bundly- loose packing allows myosin-II to enter bundle (actin filaments and alpha-actinin)
2. Parallel bundle- tight packing prevents myosin-II from entering bundle (actin filaments and fimbrin)
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| a bundle of parallel actin filaments cross-linked by the actin-bundling proteins villin and fimbrin forms the core of a _______ | microvillus
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| Lateral side arms of a microvillus are composed of ______ and ______. They connect the sides of the actin filament bundle to the overlying plasma membrane | myosin I and the Ca2+ binding protien in calmodulin
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| All the _____ ends of the actin filaments are at the tip of the microvillus, where they are embedded in an amorphous, densely staining substance of unknown composition | plus
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| These proteins use energy of ATP hydrolysis to move along microtubules or actin filaments, mediate the sliding of flilaments, and mediate the transport of cargo along filaments | motor proteins
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| all known motor proteins that move on actin filaments are members of the ______ ______ | mysoin superfamily
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| the motor protiens that move on microtubules are either members of the _____ _____ or the _____ _____ | kinesin superfamily or the dynein family
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| the only structural element shared among all members of each superfamily is the motor _____ domain | "head"
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| the tails of motor proteins help to perform different functions in the cell including... | transportation and localization of specific proteins, membrane-enclosed organelles, and mRNAs
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| what are the two distinct types of specialized structures in eucaryotic cells that are formed from highly ordered arrays of motor proteins that move on stabilized filament tracks? | the myosin-actin system of the sarcomere, and the dyenin-microtubule system of the axoneme
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| function of the myosin-actin system of the sarcomere | powers the contraction of various types of muscle such as skeletal, smooth, and cardiac muscle
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| function of the dyenin-microtubule system of the axoneme | powers the beating of cilia and the undulations of flagella
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| whole-cell movements and the large-scale shaping and structuring of the cells require: | coordinated activities of all three basic filament systems and a large variety of cytoskeletal accessory proteins, including motor proteins
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| functions of the microtubule-based mitotic spindle during cell division requires spatial and temporal cooperation between... | dynamic cytoskeletal filaments, active molecular motor proteins, and a wide variety of accessory factors
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| what are the main types of myosin? | myosin I (located in microvilli) and myosin II ( motor head for muscle contraction)
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| huge multinucleated cells form by the fusion of many muscle cell precursors, called ________ | myoblasts
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| in an adult human, a muscle cell is typically ____ mm in diameter and can be up to several centimeters long | 50 mm
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| what are the two type of microtubule motor proteins? | kinesins and dyneins
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| _____ is a motor protein that moves along microtubules. the fastest of this protein can move their microtubules at about 2-3 mm/sec | Kinesin
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| ________ are the largest of the known molecular motors, and they are also among the fastest. They are independently evolved and have distinct structure and mechanism of action. (can move microtubules in test tube 14 mm/sec) | Dyneins
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| in isolated doublet microtubules dynein produces ______ ______ | microtubule sliding
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| in normal flagellum dynein causes ________ _______ | microtubule bending
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| Dyenin movement is from ________ to _________ | positive to negative
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| What are the three classes of dynamic microtubules in the mitotic spindle at metaphase? | kinetochore microtubules (attach each chromosome to the spindle pole), interpolar microtubules (hold the two halves of the spindle together), astral microtubules (can interact with the cell cortex)
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| All of the microtubules are oriented with their _______ ends at the spindle poles where the centrosomes reside, and their ______ ends projecting away. | minus; plus
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| ______ _______ undergo dynamic instability, growing and shrinking at their plus ends | astral microtubules
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| _________ _______ and _________ __________ both undergo continuous flux toward the spindle poles | kinetochore microtubules and interpolar microtubules
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| Cell crawling is important in? | embryonic development, wound healing, tissue maintenance, immune system function
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| How does the cell coordinate cytoskeletal actions? | protrusion at the leading edge( assembly of new actin filaments) and adhesion of newly protruded part to substratum signals forces generated by molecular motors to bring the cell body forward
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| Actin-polymerization is dependent protrusion and firm attachment of a _________ at the leading edge of the cell moves the edge forward and stretches the actin cortex | lamellipodium
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| Contraction at the rear of the cell propels the body cell ___________ to relax some of the tension | Forward
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| Complex cells require the coordinated assembly of: | Microtubules, neurofilaments, action filaments, and action of dozens of highly specilized molecular motors that transport subcellular components to their appropriate destinationd
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