L22 - Microtubules

Question 1

describe microtubuke growth and catostrophe with the role of the GTP cap

Answer 1

Growth phase:
- β-tubulin at plus end binds GTP = forms GTP cap
- GTP bound comfomation is stable and allows microtubule elongation

Catastrophe:
- over time -> GTP hydroluysed to GDP on β-tubulin
- if cap is lost = microtubule becomes unstable = protofilaments fall off

= rapid depolymersaion (catasrophe)

regaining a cap via ‘rescue’ can reverse shrinkahe and restart growth

Question 2

why is the GTP cap important

Answer 2

stabilising structure at the growing end

= prescence or abdcsence determines growth or shrinkage
= enables ‘dynamic instability’

Question 3

how do stabilsing MAPs (microtubule asociated proteins) and destabilsing proteins affect microtubule behavior

Answer 3

MAPs (MAP2) - binds along microtubuke side and promote polymerisation

destabilising - enhance depolymerisation by binding tubulin dimers

Question 4

what are EB proteins

Answer 4

End binding proteins -> family of +TIPs (+ end tracking proteins)

selectively bind to GTP cap at growing mcirotubule end

= act as platform for recruitment fo other +TIPs
= stabilsie GTP-tubulin regions

Question 5

why are Eb proteins important

Answer 5

make the microtubule plus ends ‘specialised’ = enable targetted interactions with structures

= membranes or kinetochores

Question 6

why are microtubules targets for chemotherapy and name 1 drug

Answer 6

microtubules essential for mitosis –> dirupt microtubule –> cancer cell cannot divide

Taxol = stabilises microtubules –> prevents depolymerisation

= mitotic arrest + apoptosis