Module 8- Cytoskeleton I Vocabulary Matching

Actin filament and microtubule assembly where the concentration of free subunits determines the growth rate of these filaments.

Polymerize (polymerization)

Rate of addition of new subunits to the filament ends exactly balances the rate of subunit dissociation.

Critical concentration (Cc)

Protein that helps regulate the distance between adjacent microtubules. Forms bundles of stable microtubules that are closely packed together. Also forms large aggregates in neurons called neurofibrillary tangles.

Tau

Promotes microtubule elongation. Binds tubulin subunits and delivers them to the (+) ends of microtubules.

XMAP215

Family of motor proteins that bind microtubules and move towards the (-) ends of microtubules.

Dyneins

Process by which microtubules are constantly switching between rapid growth and rapid shrinkage.

Dynamic instability

The rate limiting step in filament formation. Spontaneous assembly of a few subunits is unstable until the initial oligomer is stabilized by multiple subunit-subunit contacts; then elongation is rapid afterwards.

Nucleation

A dense spherical matrix recruited by the centrioles where microtubule nucleation occurs.

Pericentriolar material

Soluble subunits of microtubules. Are composed of GTP-bound ⍺ and proteins.

Tubulin dimers

Protein that binds to tubulin subunits and prevents their addition to microtubules. Sequesters free tubulin dimers and maintains the pool of active subunits near the critical concentration.

Stathmin

Proteins that bind to microtubules to regulate the length, stability, number and geometry of microtubules.

Microtubule-associated proteins (MAPs)

A single long, whip-like protrusion whose undulations propel a cell through a fluid. In eukaryotic cells, these are a longer version of cilia.

Flagella

Process by which filaments remain the same length overall due to addition of subunits at the (+) end at the same rate as loss of subunits at the (-) end.

Treadmilling

Superfamily of motor proteins that almost all move towards the (+) ends of microtubules (one exception)

Kinesins

A bundle of microtubules (9 outer doublet microtubules and 2 central single microtubules) that forms the core of both cilia and flagella and is responsible for their movement.

Axonemes

Sites that are rich in γTuRC. In most animal cells, these are located near the cell nucleus.

Microtubule-organizing centers (MTOCs)

An initial oligomer of subunits that is stabilized by subunit-subunit interactions.

Nucleus

Proteins that bind to the (+) ends of microtubules and increase the rate of microtubule depolymerization.

Catastrophe factors

Dynein-mediated movement of cargo towards the (-) end of microtubules.

Centripetal movement

A short cylindrical array of microtubules; similar to a basal body. In animal cells, they are found as a pair in the center of a centrosome.

Centrioles

Process by which all cilia and flagella grow from basal bodies.

Intraflagellar transport

Rapid elongation of microtubules due to regaining their GTP-cap.

Rescue

Actin filament and microtubule disassembly where the rate of subunit loss is constant.

Depolymerize (depolymerization)

Composed of monomer proteins organized into a ring-shaped structure with other associated proteins. After nucleation, it remains bound to the (-) end of the microtubule preventing subunit gain or loss.

γ-tubulin ring complexes (γTuRC)

Tightly attached to axonemes by their tails to the A tubule. Their motor heads make transient ATP-dependent attachments to the B tubule of the adjacent doublet.

Dynein arms

Kinesin mediated movement of cargo towards the (+) end of microtubules.

Centrifugal movement

Found on the apical surface of some epithelial cells. Beat in a whip-like motion to either propel a single cell through fluid or to move fluid across the epithelial cell surface.

Cilia

Found at regular intervals along the axoneme and help to attach adjacent microtubule doublets.

Nexin links

A large protein complex that associates with cytoplasmic dynein in order to efficiently transport most organelles

Dynactin

Primary microtubule-organizing center in animal cells and acts as the spindle pole during mitosis. Contains a pair of centrioles.

Centrosome

Human diseases linked to defects in motile and primary cilia.

Ciliopathies

Protein that severs microtubules near the centrosome.

Katanin

Plasma membrane associated structures that anchor flagella, motile cilia and nonmotile cilia to the cell surface. The core of these structures contains a single centriole with 9 groups of fused microtubule triplets arranged in a cartwheel.

Basal bodies

Proteins that bind to the (+) or (-) end, respectively, and prevent gain or loss of subunits from the filament.

Capping proteins

Most cells contain 1 of these structures that are non-motile and located on its cell surface. It acts as a mechanical and sensory receptor, but is non-motile due to a lack of dynein arms.

Primary cilia

Rapid shrinkage of microtubules due to loss of the GTP-cap due to nucleotide hydrolysis

Catastrophe

Protein that helps regulate the distance between adjacent microtubules. Forms bundles of stable microtubules that are widely spaced apart.

MAP2

Trafficking of vesicles or organelles along axonal microtubules from cell body to axon terminal carried out by kinesins

Anterograde movement

The longitudinal arrangements of subunits, which run the length of the filament. Linear strings of subunits joined end to end to provide strength and adaptability to actin filaments and microtubules.

Protofilaments

A triphosphate subunit on the plus end of a filament that stabilizes the filament and promotes elongation.

GTP cap/ATP cap

Trafficking of vesicles or organelles along axonal microtubules from axon terminal to cell body carried out by dyneins.

Retrograde movement