Lecture 7 - Microtubules Flashcards
What are microtubules composed of?
alpha-beta tubulin heterodimers
Shape of microtubules
Hollow, tube like cylinder
What do microtubules take part in
Cell polarity, cell motility, structural support, and intracellular transport
Diameter of tube like cylinder
25nm
GTP binding sites in ab tubulin heterodimer
Both have GTP binding sites
GTP never hydrolysed by alpha tubulin
GTP hydrolysed by beta tubulin when heterodimer incorporated in microtubule
How do microtubule-binding drugs work?
- Prevent microtubule assembly (colchicine) or disassembly (cancer drug taxol)
- Inhibits cellular processes that depend on microtubules and polymer rearrangement
GTP on alpha-tubulin
- Never hydrolysed or exchanged with free nucleotide
GTP on beta-tubulin
- Hydrolyses bound GTP to GDP
- Exchanges GDP for GTP after subunit disassembles
Size of ab-tubulin dimer
8nm
Microtubule singlets, doublets, triplets
- Singlet
- Doublet e.g. cilia, flagella (9+2 arrangement)
- Triplet e.g. basal bodies, centrioles
Microtubule organzing centres (MTOCs)
- Nucleate and organise microtubules
- Almost all microtubules originate from MTOCs
- (-) ends associate with MTOC
Main MTOC in animal cells?
Centrosomes
Are spindle poles a MTOC?
Yes
Where is MTOC located in nerve cells?
Base of axon
What are basal bodies?
- MTOC that incorporates into ‘mother centriole’ - the centriole inherited from previous division