3. Microtubules

Question 1

what are microtubules composed of

Answer 1

alpha and beta Tubulin heterodimers

Question 2

what do Tubulin dimers bind

Answer 2

GTP

Question 3

what does:

• alpha Tubulin do to GTP
• beta Tubulin do to GTP

Answer 3

alpha = maintains, NEVER hydrolysed or exchanged
beta = hydrolyses into GDP

Question 4

what is the effect of taxol on beta tubulin

Answer 4

prevents disassembly of mitotic spindle following cell division ->
prevents cancer cells from dividing

Question 5

when does GDP get exchanged for GTP in beta tubulin

Answer 5

once the subunit disassembles

Question 6

microtubules are polarised, which end is the:
- end
+ end

Answer 6

• end = alpha tubule

+ end = beta tubule

Question 7

give an example of where microtubules are found in doublets

Answer 7

cilia, flagella

Question 8

give an example of where microtubules are found in triplets

Answer 8

centrioles

Question 9

what is the term for inter-doublet connections

Answer 9

nexin linkages

Question 10

what is the purpose of microtubule organising centres (MTOCs)

Answer 10

nucleate and organise microtubules

Question 11

which end of a microtubule is associated to a MTOC

Answer 11

• end

Question 12

give an example of a MTOC

Answer 12

centrosome, spindle poles

Question 13

what nucleates most microtubules

Answer 13

gamma-tubulin ring complex

Question 14

where are gamma-tubulin ring complexes found

Answer 14

in the pericentriolar material of a MTOC

Question 15

when must dimer formation occur

Answer 15

before the growth of the microtubule

Question 16

describe critical concentration in the dimers

Answer 16

the + end has lower critical concentration, this allows growth at the + end

Question 17

what is dynamic instability

Answer 17

when microtubule ends have beta tubulin bound to GDP, the microtubule is unstable and quickly disassembles

this continues until a GTP cap is formed

Question 18

what is the role of microtubule associated proteins (MAPs)

Answer 18

bind to, stabilise and promote assembly

Question 19

describe tau in alzheimers

Answer 19

fragile and unfolded nature making it liable to structural abnomralities

in alzheimers, tau forms aggregates clumping together impairing cognitive function

Question 20

describe the role of EB1

Answer 20

end binding 1 is a (+)end tracking protein that stimulates rescue and regrowth of microtubules

Question 21

describe the role of kinesin 13

Answer 21

facilitates disassembly by hydrolysing ATP

Question 22

describe the role of stathmin

Answer 22

binds to curves protofilaments and enhances disassembly.

Question 23

why do cells modify their dynamic instability

Answer 23

so they can become more dynamic as cells enter mitosis

Question 24

microtubules are composed of how many laterally associated protofilaments

Answer 24

13