Microtubules and intermediate filaments

Question 1

key role of microtubules

Answer 1

resist compressive force

Question 2

what processes are microtubules involved in?

Answer 2

mitosis and meiosis to ensure separation of chromosomes
tracks for vesicle trafficking
cilia and flagella

Question 3

microtubule structure

Answer 3

alpha and beta tubulin form heterodimers
repeating unit
polar ends (beta tubulin on + end)
form protofilaments that are laterally associated with eachother with alpha aligning with alpha and beta with beta
staggered spiral structure

Question 4

GTP and GDP with alpha and beta tubulin

Answer 4

GTP can bind to both alpha and beta tubulin
but only beta tubulin can hydrolyse the GTP to GDP

Question 5

why do heterodimers assemble at the + end

Answer 5

when beta tubulin is bound to GTP, the molecular association between subunits is stronger

Question 6

GTP hydrolysis on beta tubulin

Answer 6

more likely to occur when in polymerised form.
causes conformational change that curves the protofilament, weakening the lateral associations between protofilaments.
depolymerisation at the positive end

Question 7

GTP cap

Answer 7

stabilises growing microtubules, preventing depolymerisation

Question 8

microtubule catastrophe

Answer 8

GTP hydrolysis rate > rate of heterodimer addition
rapid shrinkage from positive end

Question 9

dynamic instability of microtubules

Answer 9

cycles of growth and collapse

Question 10

microtubule binding proteins

Answer 10

regulate growth and shrinkage of microtubules

Question 11

where do microtubules comes from

Answer 11

microtubule organising centre
nucleating complexes, eg pericentrin

Question 12

how are new microtubules formed

Answer 12

grow from gamma tubulin ring complexes of the centrosome