Chapter 18: Cell Organization & Movement II: Microtubules Flashcards

unstable

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

GTP

Assembled tubulin hydrolyzes ________

MAPs

__________ mediate the assembly, dynamics, and function of microtubules

microtubules

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

microtubule organizing centers

what does MTOC stand for

centrosome

________________ MTOCs consist of two centrioles and the surrounding pericentriolar material

intermediate

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

microtubules

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

microfilaments

microtubules

intermediate filaments

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

tracks

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

microtubule

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

tubulin dimer

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

genes

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

alpha tubulin

tubulin dimer: GTP is never hydrolyzed and nonexchangeable

beta tubulin

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

tube

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

protofilaments

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

polarity

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

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.

microtubule

Dimer alignment provides structural polarity to the __________________

positive

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

singlet

_____________ microtubule: 13 protofilaments - most cytoplasmic MTs

cytoplasm

where are the singlet microtubules located?

cilia, flagella

where are the doublet microtubules located?

basal bodies, centrioles

where are the triplet microtubules located?

doublet microtubule

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

triplet microtubule

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

microtubules

_______________ are assembled from MTOCs to generate diverse configurations

interphase, mitosis

MT distribution: immunofluorescence microscopy using antibodies to tubulin

•(a) _______________ cell

•(b) Cell in ______________

distribution

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

centrosome

microtubule, Interphase cell: _______________ MTOC

mitotic

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

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

cilium, flagellum

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

dendrites

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

animal

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

daughter

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

templated

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

plants

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

negative

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

template

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

instability

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

store

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

cytoplasm

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

microtubules

dynamic structures that can assemble or disassemble rapidly at both ends

positive

Microtubules grow preferentially at the ____________ end

individual

____________ microtubules exhibit dynamic instability

lengths

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

rapid

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

catastrophe, rescue

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

assembling

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

disassembling

_______________ MT: splaying curled protofilaments

GTP-β-tubulin cap

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

end

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

assembly

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

protofilament

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

disassembly

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

greater

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

rescue

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

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

GDP

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

stabilize

Side-binding MAPs _______________ microtubules

end

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

catastrophe

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

spacing

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

space

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

greater

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

greater

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

stabilize

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

regulate

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

positive

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

antibodies

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

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

growth

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

CLASPs

____________ reduce frequency of catastrophes

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

kinesin 13

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

ATPase

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

dissociation

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

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.

organelles

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

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

cytoplasmic dynein

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

post translational

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

kinesin 1

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

kinesin 1

homodimer of two identical heavy chains

head motor domain

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

flexible linker domain

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

tail

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

microtubule, nucleotide, linker

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

surface

kinesin 1: Attaches to a vesicle __________ receptor

transports

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

fourteen

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

conserved

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

transport

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

vesicle

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

heavy

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