BIOL 3030 - LEC 13 - Vocabulary

Vocabulary flashcards covering composition, dynamics, regulation, motors, drugs, and microtubule-based structures discussed in Lecture 13 on microtubules.

Microtubule

Hollow, 25-nm cytoskeletal filament composed of 13 protofilaments of α/β-tubulin dimers that provides structural support and tracks for intracellular transport.

α-/β-Tubulin Dimer

Heterodimeric building block of microtubules in which α-tubulin binds a non-hydrolyzed GTP and β-tubulin binds an exchangeable, hydrolyzed GTP.

Protofilament

Linear chain of α/β-tubulin dimers; thirteen associate laterally to form one microtubule cylinder.

Microtubule Seam

Single longitudinal interface where the helical lattice of protofilaments is offset, creating a structural discontinuity.

(+) End

Fast-growing microtubule end, typically oriented toward the cell periphery; rich in GTP-β-tubulin during growth.

(−) End

Slow-growing microtubule end, usually anchored in an MTOC and capped by γ-tubulin complexes.

Microtubule Organizing Center (MTOC)

Cellular site, such as the centrosome or basal body, that nucleates and anchors the (−) ends of microtubules.

Centrosome

Primary MTOC of animal cells consisting of a pair of centrioles surrounded by pericentriolar material containing γ-TURC.

Centriole

Cylindrical structure of nine triplet microtubules (9+0) that helps form centrosomes, basal bodies, and spindle poles.

Basal Body

Modified centriole that nucleates the axoneme of cilia or flagella.

γ-Tubulin Ring Complex (γ-TURC)

Protein complex that templates microtubule nucleation by mimicking a ring of 13 tubulin subunits, capping the (−) end.

Dynamic Instability

Behavior in which individual microtubules stochastically switch between phases of growth and rapid shrinkage (catastrophe) and regrowth (rescue).

GTP Cap

Terminal region of GTP-β-tubulin that stabilizes a growing microtubule; its loss triggers catastrophe.

Catastrophe

Transition from microtubule growth to rapid depolymerization when the GTP cap is lost.

Rescue

Transition from depolymerization back to growth when a new GTP cap is re-established.

Colchicine

Drug that binds free tubulin dimers and blocks their polymerization, leading to microtubule depolymerization.

Nocodazole

Microtubule-depolymerizing drug that disrupts polymerization by binding β-tubulin.

Taxol (Paclitaxel)

Anticancer drug that stabilizes microtubules by binding their walls and preventing depolymerization.

Microtubule-Associated Protein (MAP)

Protein that binds microtubules to regulate their stability, spacing, or interactions with other cellular structures.

Tau

Axonal MAP that stabilizes microtubules and is implicated in neurodegenerative diseases when hyperphosphorylated.

MAP2

Dendritic MAP that stabilizes and cross-links microtubules at greater spacing than Tau.

MAP4

Ubiquitous cytoplasmic MAP that stabilizes microtubules in non-neuronal cells.

+TIPs (Plus-End Tracking Proteins)

Proteins that specifically associate with growing (+) ends to promote polymerization or link microtubules to other structures.

Kinesin

ATP-dependent motor protein superfamily that generally moves cargo toward the (+) ends of microtubules.

Kinesin-1

Conventional dimeric kinesin responsible for most anterograde organelle and vesicle transport.

Kinesin-2

Heterotrimeric motor involved in vesicle transport and intraflagellar transport (IFT).

Kinesin-5

Bipolar kinesin that slides antiparallel microtubules apart during mitotic spindle assembly.

Kinesin-13

Depolymerizing kinesin that binds microtubule ends to induce disassembly rather than motility.

Dynein

Large minus-end–directed AAA-ATPase motor responsible for retrograde transport, mitotic spindle positioning, and ciliary beating.

Cytoplasmic Dynein

Dynein form that transports organelles, vesicles, and mRNA toward the (−) ends of microtubules.

Axonemal Dynein

Dynein variant attached to doublet microtubules in cilia/flagella that generates bending by sliding adjacent doublets.

Axonal Transport

Bidirectional movement of organelles and proteins along axonal microtubules by kinesin and dynein motors.

Mitotic Spindle

Microtubule-based apparatus that segregates chromosomes during mitosis; composed of kinetochore, astral, and interpolar MTs.

Axoneme

Core of cilia and flagella with a 9+2 arrangement of microtubule doublets and associated proteins.

Nexin Linker

Elastic protein that connects adjacent doublets in the axoneme, limiting sliding and converting it into bending.

Primary Cilium

Single, non-motile microtubule-based projection acting as a sensory signaling organelle on most vertebrate cells.

Ciliopathy

Group of diseases caused by defects in cilia structure or function, e.g., polycystic kidney disease.

Filopodium

Actin-based finger-like projection; not microtubule-based.

Microvillus

Actin-filled brush-border projection; distinct from cilia.

Dynamic Torsional Energy

Stored strain in straight protofilaments released during catastrophe to power rapid depolymerization.