Chapter 18: Cell Organization & Movement II: Microtubules Flashcards

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203 Terms

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unstable

αβ-Tubulin assembles into dynamically _________ and polarized microtubules with (+) and (-) ends and 13, 13+10, and 13+10+10 protofilament walls

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GTP

Assembled tubulin hydrolyzes ________

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MAPs

__________ mediate the assembly, dynamics, and function of microtubules

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microtubules

All ________________ are nucleated from microtubule-organizing centers (MTOCs), and many remain anchored by their (−) ends

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microtubule organizing centers

what does MTOC stand for

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centrosome

________________ MTOCs consist of two centrioles and the surrounding pericentriolar material

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intermediate

________________ ________________ cytokeratins (red) connected to desmosomes (yellow) in epithelial cells. Intermediate filaments also line the inner surface of the nucleus

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microtubules

________________ (green) and the Golgi complex (yellow), which is centrally located by transport along microtubules

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microfilaments

knowt flashcard image
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microtubules

knowt flashcard image
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intermediate filaments

knowt flashcard image
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cilia

__________ projecting from the surface of the ciliated epithelium lining a rabbit oviduct. Each cilium contains a core motile MT structure, which beats to propel eggs down the oviduct

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tracks

Microtubules and intermediate filaments in a nerve axon provide __________ for intracellular vesicle motility and axon structural stability, respectively

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microtubule

______________ cross section showing ends of the 13 protofilaments that form the MT wall.

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tubulin dimer

•omposed of stably associated, highly conserved (in eukaryote), and structurally similar α-tubulin and β-tubulin monomers (55kDa MW).

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genes

Most eukaryotes have several ___________ encoding both dimers and additional genes encoding a gamma-tubulin subunit, which is involved in MT assembly

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alpha tubulin

tubulin dimer: GTP is never hydrolyzed and nonexchangeable

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beta tubulin

tubulin dimer: GDP is exchangeable with GTP, which can be hydrolyzed in the site

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tube

Tubulin subunit organization in a microtubule: forms a structurally polarized _________

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protofilaments

Dimers are aligned end-to-end in the same orientation into _______________

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polarity

Protofilaments pack side by side with the same subunit ____________ to form the wall of the microtubule

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staggered

Protofilaments are slightly _________________ so that α-tubulin in one protofilament is in contact with α-tubulin in the neighboring protofilaments, except at the seam, where an α-subunit contacts a β-subunit.

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microtubule

Dimer alignment provides structural polarity to the __________________

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positive

Subunits are added preferentially at the ___________ end where β-tubulin monomers are exposed

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singlet

_____________ microtubule: 13 protofilaments - most cytoplasmic MTs

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cytoplasm

where are the singlet microtubules located?

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cilia, flagella

where are the doublet microtubules located?

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basal bodies, centrioles

where are the triplet microtubules located?

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doublet microtubule

an additional wall of 10 protofilaments forms a second tubule (B) in cilia/flagellar outer doublets

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triplet microtubule

two 10-protofilament walls (B) and (C) on the 13-protofilament (A) microtubule in centriole and basal body microtubule organizing centers

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microtubules

_______________ are assembled from MTOCs to generate diverse configurations

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interphase, mitosis

MT distribution: immunofluorescence microscopy using antibodies to tubulin

•(a) _______________ cell

•(b) Cell in ______________

<p>MT distribution: immunofluorescence microscopy using antibodies to tubulin</p><p>•(a) _______________ cell</p><p>•(b) Cell in ______________</p>
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distribution

microtubule ________________ in various cells and structures - assembled from distinct MTOCs (Microtubule polarity is indicted by (+) and (−).)

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centrosome

microtubule, Interphase cell: _______________ MTOC

<p>microtubule, Interphase cell: _______________ MTOC</p>
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mitotic

microtubule, In a _________ cell: two spindle pole centrosome MTOCs organized two MT arrays

<p>microtubule, In a _________ cell: two spindle pole centrosome MTOCs organized two MT arrays</p>
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neuron

microtubule, ____________: microtubules in both axons and dendrites are assembled from an MTOC in the cell body and then released from it. Dendrite MTs have mixed orientation

<p>microtubule, ____________: microtubules in both axons and dendrites are assembled from an MTOC in the cell body and then released from it. Dendrite MTs have mixed orientation</p>
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cilium, flagellum

microtubule, ____________/______________: microtubules are assembled on a basal body MTOC

<p>microtubule, ____________/______________: microtubules are assembled on a basal body MTOC</p>
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dendrites

In all but _______________, the MT (-) end is attached to or oriented toward the MTOC

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animal

___________-cell centrosome: two centrioles at right angles to each other, surrounded by pericentriolar material (arrows

<p>___________-cell centrosome: two centrioles at right angles to each other, surrounded by pericentriolar material (arrows</p>
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daughter

Mother, with distinctive distal appendages (blue spheres), and _____________ centrioles each consists of nine linked triplet microtubules

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templated

The daughter centriole is _____________ by a nine-fold symmetric cartwheel structure that is later removed

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plants

_________ do not have centrosomes and basal bodies, but use other mechanisms to nucleate the assembly of microtubules

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negative

Microtubules assembled in vitro (green) with a γ-TuRC (red) at the ____________ end

<p>Microtubules assembled in vitro (green) with a γ-TuRC (red) at the ____________ end</p>
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template

Model of γ-TuRC nucleation of microtubule assembly − forms a _______________ for the MT (−) end.

<p>Model of γ-TuRC nucleation of microtubule assembly − forms a _______________ for the MT (−) end.</p>
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instability

Individual microtubule (+) ends exhibit dynamic ______________ with alternating periods of growth and rapid disassembly (catastrophe), depending on GTP-cap or GDP-cap status

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store

Assembling microtubules __________ energy derived from GTP hydrolysis in the microtubule lattice and can do work when disassembling.

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cytoplasm

Dynamically unstable microtubules can "search" the ______________ and "capture" targeted structures or organelles

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microtubules

dynamic structures that can assemble or disassemble rapidly at both ends

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positive

Microtubules grow preferentially at the ____________ end

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individual

____________ microtubules exhibit dynamic instability

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lengths

Microtubule ___________ (observed with light microscopy) plotted over time exhibit dynamic instability

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rapid

Assembly and disassembly of microtubules each proceed at uniform rates, but disassembly is much more ___________ (7 μm/min) than assembly (1 μm/min).

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catastrophe, rescue

MT (+) ends make abrupt transitions from elongation to shrinking (______________) back to elongation (___________)

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assembling

____________ MT: blunt end or curving sheet not yet closed at seam

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disassembling

_______________ MT: splaying curled protofilaments

GTP-β-tubulin cap

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lateral

GTP-β-tubulin cap: ___________ protofilament--protofilament interactions in the GTP-β-tubulin cap are sufficiently strong to prevent protofilament unpeeling at the MT end

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end

GTP-β-tubulin cap: MT with GTP-β-tubulin on the ________ of each protofilament

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assembly

GTP-β-tubulin cap: Strongly favors ___________ by adding more GTP-tubulins

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protofilament

GDP-β-tubulin cap: MT with GDP-β-tubulin at the end of each _____________

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disassembly

GDP-β-tubulin cap: Protofilaments curve and undergo rapid ______________

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greater

switch from assembly to disassembly (catastrophe): rate of GTP hydrolysis (constant) is _______________ than rate of GTP-tubulin addition.

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rescue

Switch from disassembly to assembly (___________): rate of GTP-tubulin addition is greater than rate of GTP hydrolysis

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GTP beta tubulin islands

(detected with an antibody specific for GTP-β-tubulin) can persist along the length of an assembled microtubule. When a disassembling microtubule encounters a GTP-β-tubulin island, disassembly pauses and rescue may be initiated

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GDP

Disassembled GDP-β-tubulin exchanges GTP for ___________ to become GTP-β-tubulin

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stabilize

Side-binding MAPs _______________ microtubules

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end

(+) ________-binding +TIPs can alter microtubule dynamic properties or attach cell components to the (+) end

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catastrophe

Microtubule ends are destabilized by proteins such as the kinesin-13 family of proteins and Op18/stathmin, which enhance _________________ frequency

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spacing

_____________ of microtubules depends on the length of the projection domains of microtubule associated proteins

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space

MAP (long arm) and tau (short arm) side-binding proteins − stabilize and ___________ MTs

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greater

MT spacing in MAP2-expressing cells is ______________ than in tau-expressing cells - enlarges caliber of cell

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greater

MAP-MT associations: MT spacing in MAP2-expressing cells is ______________ than in tau-expressing cells - enlarges caliber of cell

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stabilize

MAP-MT associations: Side associations with several monomers along protofilaments ______________ MTs and dampen dynamic instability

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regulate

MAP-MT associations: MAP/tau phosphorylation can ____________ MT interactions

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positive

+TIPs regulate the properties and functions of the microtubule _______________ end

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antibodies

Cell stained with ______________ to tubulin (red) and the EB1 +TIP protein (green) enriched on MT (+) ends

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kymograph

________________ (image slices over time) of EB3-GFP shows association only with growing MT end - binds only to straight GTP-capped ends and not to curved GDP-capped protofilaments on disassembling MTs

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growth

EB1 and XMAP215 promote microtubule ______________ by enhancing polymerization at the (+) end

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CLASPs

____________ reduce frequency of catastrophes

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captured

A third class of +TIPs can become "____________" and stabilized by other proteins to link the microtubule (+) end to other cellular structures, such as the ER, F-actin in the cell cortex, and chromosomes during mitosis

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kinesin 13

Enhances the disassembly of either a (+)/(-)-MT end

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ATPase

_____________ activity dissociates Kinesin-13 from the αβ-tubulin dimer

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dissociation

Op18/stathmin binds selectively to two dimers in curved protofilaments and enhances their _______________ from a MT end.

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growth

Op18/stathmin binding: Activity is inhibited by phosphorylation, which is inhibited at a cell's leading edge, contributing to MT _____________ at front of cell.

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organelles

The kinesin (+)end motor superfamily transports _____________ and slides antiparallel microtubules past each other.

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kinesin 1

__________-___ is a highly processive motor because it coordinates ATP hydrolysis by its two heads so that one head is always firmly bound to a microtubule

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cytoplasmic dynein

_______________ ____________ is a (−)end motor that associates with the dynactin complex and cargo adapters to transport cargo

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post translational

Tubulin __________-__________________ modifications stabilize microtubules and regulate ability to interact with motor

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kinesin 1

___________-_____ powers vesicle movement down axons toward the (+) ends of microtubules

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kinesin 1

homodimer of two identical heavy chains

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head motor domain

kinesin 1, heavy chains: MT and ATP/ADP binding sites

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flexible linker domain

kinesin 1, heavy chains: required for motor activity and connects head to the coiled-coil stalk

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tail

kinesin 1: •Two light chains associated with the _______ of each heavy chain bind to receptors on vesicles

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microtubule, nucleotide, linker

Kinesin head domains: _______________-binding site, ________________-binding sites (contains ADP), ___________ regions connect heads to stalks

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surface

kinesin 1: Attaches to a vesicle __________ receptor

<p>kinesin 1: Attaches to a vesicle __________ receptor</p>
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transports

kinesin 1: _______________ vesicles from the (−) end to the (+) end of a stationary microtubule

<p>kinesin 1: _______________ vesicles from the (−) end to the (+) end of a stationary microtubule</p>
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fourteen

______________ known classes of kinesins form a large protein superfamily with diverse functions. (45 kinesin genes in the human genome)

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conserved

A ______________ motor domain is fused to a variety of class-specific nonmotor domains

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transport

Kinesin-1: (+) end-directed microtubule motor involved in organelle ____________

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vesicle

kinesin-2: (+) end-directed ___________ transport

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heavy

kinesin-2: Family has two closely related but nonidentical ____________ chains and a third cargo-binding subunit