Microtubules Flashcards
What is the difference between GTP in alpha and beta tubulin?
- In beta GTP is hydrolysable and exchangable
- Alpha tubulin remains GTP bound
What is the structure of microtubules?
- alpha and beta tubulin heterodimer stack to form protofilaments
- 13 protofilaments assemble
Which end do filaments grow more quickly in?
Plus end
What is the structure of centrioles?
Composed of 9 sets of microtubules
What is the structure of centrosomes?
- 2 centrioles held together by SAS-6 prortein
Where does microtubule nucleation occur?
- Gamma tubulin ring complexes of the Centrosome
Why is a nucleator needed for microtubule formation?
Spontaneous growth is slow
What is the role of γ-tubulin in nucleation of microtubules?
γ-tubulin is arranged to form the template from which the structure of the growing mt can be defined
What occurs in microtubule formation in vitro?
- Slow phase through unstable early assembly intermediates
- Once a sufficiently large oliger is formed by N steps assembly is energetically favoured
- Filaments are more likely to disassemble
What occurs in microtubule formation in vivo?
- preformed nuclei allow microtubule growth to bypass slow phase
- Favourable and quick formation
- Provides spatial and temporal control over growth
What complex is crucial for microtubule nucleation?
γ-tubule ring complex
What is the structure of γ-tubulin ring complex?
- 14 γ-tubulins are arranged in a spiral with a half subunit overlap so only 13 γ-tubulins avaliable as a template
Where does formation of the microtubule seam occur?
Along the same axis as overlap between γ-tubulin in γ-tubulin ring
Why does formation of a microtubule seam occur?
- Caused by different laterla contacts between tubulin subunits
What can alter microtubule stability, anchoring, and direct branching?
Attachment factors
