Introduction to the Cytoskeleton: Microtubules

A set of vocabulary flashcards covering the structure, dynamics, regulatory proteins, and functions of microtubules based on the introductory cytoskeleton lecture.

Cytoskeleton

The skeleton of the cell, formed from a network of filament polymers that provide shape, strength, organisation, and movement.

Microtubules

Polymers of globular $\alpha$ and $\beta$ tubulin dimers that associate as 13 protofilaments to form a stiff, hollow tube.

Subunit Proteins

Proteins that associate via multiple non-covalent bonds to form cytoskeletal filaments, allowing for both strength and rapid disassembly.

Centrosome

The microtubule organising centre located in the cell centre; it is comprised of centrioles surrounded by pericentriolar material.

Microtubule Polarity

The structural orientation of microtubules featuring a 'plus' ($+$) end where subunits are added and a 'minus' ($-$) end usually anchored at the centrosome.

Dynamic Instability

The property of microtubules to rapidly grow or shrink, primarily at the plus end, powered by GTP hydrolysis.

GTP hydrolysis

The process where GTP-bound tubulin dimers added to the plus end are converted to GDP, causing a conformational change that weakens bonds and promotes dissociation.

Catastrophe

The rapid depolymerisation of a microtubule that occurs if the GTP cap is hydrolysed more quickly than new dimers are added.

Rescue

The resumption of microtubule growth that occurs when dimer addition becomes faster than GTP hydrolysis, restoring the GTP cap.

GTP cap

A protective layer of recently added GTP-bound tubulin at the plus end of a microtubule that prevents depolymerisation.

Microtubule Associated Proteins (MAPs)

Proteins that bind to the sides or ends of microtubules to regulate their organisation, stability, and dynamics.

Tau

A MAP that binds to the sides of microtubules in neurons to stabilize them and cross-link adjacent filaments along axons.

Kinesin-13

An end-binding protein that promotes microtubule catastrophe and disassembly by stabilising the curved conformation of tubulin dimers.

$\gamma$-TuRC

A protein complex that nucleates microtubule assembly and remains associated with the minus end.

+TIPS

Proteins that remain associated with growing plus ends and can link them to other structures like membranes.

XMAP215

A MAP that stabilizes plus ends and accelerates the assembly of microtubules.

Katanin

An accessory protein that severs microtubules.

Stathmin

A protein that binds to tubulin subunits to prevent their assembly into microtubules.

Dynein

A microtubule motor protein that 'walks' towards the minus end (towards the cell centre).

Kinesins

A family of microtubule motor proteins that generally 'walk' towards the plus end (towards the cell periphery).

ATP hydrolysis

The chemical process that powers the walking motion of motor proteins through conformational changes in their head domains.

Motor Protein Head Domain

The part of a microtubule motor protein that binds directly to the microtubule.

Motor Protein Tail Domain

The part of a microtubule motor protein that binds to cargo, such as organelles or vesicles.

Cell Polarity

The distinct protein composition and function of different faces of the plasma membrane, determined by the directionality of microtubules.

Cilia

Adapted motile microtubule structures found on airway epithelium that use a power stroke and recovery stroke for movement.

Flagella

Adapted motile microtubule structures used for movement by sperm cells and single-celled protozoa.