Ch 18

Flashcards on Microtubules and Intermediate Filaments

αβ-Tubulin

Assembles into dynamically unstable and polarized microtubules with (+) and (–) ends and 13, 13+10, and 13+10+10 protofilament walls.

MAPs (Microtubule-Associated Proteins)

Mediate the assembly, dynamics, and function of microtubules.

Microtubule-organizing centers (MTOCs)

All microtubules are nucleated from these.

Centrosome MTOCs

Consist of two centrioles and the surrounding pericentriolar material.

γTuRC (γ-tubulin ring complex)

MT nucleating structures contained in pericentriolar material.

Dynamic instability

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

+TIPs (+ End Tracking proteins)

Can alter microtubule dynamic properties or attach cell components to the (+) end.

Kinesin-13

Enhances the disassembly of either a (+)/(–)-MT end; ATPase activity dissociates it from the αβ-tubulin dimer.

Op18/stathmin

Binds selectively to two dimers in curved protofilaments and enhances their dissociation from a MT end.

Kinesin

A (+)end motor superfamily that transports organelles and slides antiparallel microtubules past each other.

Kinesin-1

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

A (−)end motor that associates with the dynactin complex and cargo adapters to transport cargo.

Dynactin complex

Links dynein to cargo.

Cilia/flagella

Cell-surface projections with a central pair of singlet MTs and nine outer doublet MTs.

Axonemal dynein

Motors attached to the A tubule on one doublet produce force on the B tubule of another to bend cilia and flagella.

Intraflagellar transport (IFT) system

Transports material to the tip by kinesin-2 activity and from the tip back to the base by cytoplasmic dynein activity in cilia/flagella.

Primary cilium

A nonmotile structure on most cells that functions as a signal antenna.

Intermediate Filaments (IFs)

Nonpolar fibrous filaments composed of five classes of IF proteins.

Lamins (Class V IFs)

Underlie and support the membrane structure of all eukaryotic nuclei. Interact with chromosomes and the cytoskeleton.

Intermediate filament–associated proteins (IFAPs)

Attach intermediate filaments to other structures.

Plakins (including plectin)

Attach intermediate filaments to other structures.