L21 - Microtubules Flashcards
(9 cards)
what are microtubules and describe structure
hollow cylindrical polymers made of tubulin dimers
= alpha + beta tubulin
tubulin dimers polymerise to form ‘protofilaments’
describe the polarity of microtubules
plus end (+) - fast growing = β-tubulin exposed
minus end (-) - slow growing/anchored = ⍺-tubulin exposed
= polarity is crucial for directed transport with mtor proteins
what is dynamic instability
rapid switchong between growth and shrinkage of microtubules
phases:
- Growth
- Catastrophe
- Shrinkage
- Rescue
describve the 4 stages of dynamic instability
Growth (polymerisation) = Tubulin-GTP dimers add to + end
Catastrophe = sudden switch from growth to shrinkage whne GTP cap is lost
Shrinkage (depolymerisation) = Tubulin-GDP subunits fall off
Rescue = regaining of GTP cap -> microtubule begins to grow again
why is dynamic instability important
allows cells to rapidly reorganise their cytoskeleton
- mitosis
- cell shape change
what is the primary microtubule-organisng centre (MTOC) in cells
centrosome
describe the key compoents of centrosome (MTOC)
2 centrioles –> cyclindrical structures made of microtuble triplets
Pericentriolar material (PCM) –> matrix surrounding centrioles
= high conc of microtubule nucleating proteins = include y-TuRCs
y-TuRCs (gamma-tubulin ring complexes) = microtubule nulceation sites
what are y-TuRCs
Gamma-Tubulin ring complex
large protein complex that contains:
- y-tubulin = homologous of a/b-tubulin
- accessory proteins that form ring-shaped scaffold
involved in microtubule nucleation
describe the microtubule nucleation due to energeticalaly unfavorable without help
Mimics microtubule minus end –> provide template for a/B-tubulin dimers to START polymerising
localised to the PCM of centrosome
= anchors microtubukes at ‘Minus’ end –> ‘Plus’ end explores cytoplasm
