Lecture 9 - microtubules and actin filaments

Question 1

what are microtubule subunits

Answer 1

tubulin heterodimers
theyre made up of one alpha and one beta tubulin

Question 2

diff between plus and minus ends in MT

Answer 2

plus = grow fast
also shrink at this end

minus = very little if any movement

Question 3

what element necassary to form micotubules in a test tube

Answer 3

Mg2+

Question 4

why cant tubulin polymerise spontaneously

Answer 4

too little concentration

Question 5

what is used to speed up tubulin polymerisation

Answer 5

gamma-tubulin and other proteins
process is called nucleation
it gives it a surface to attach to and polymerise from there

Question 6

in basal bodies what do MT form

Answer 6

bundles of MT form in the cillia

Question 7

what are MT embedded in

Answer 7

centrosome

Question 8

what is dynhamic instability

Answer 8

MT switch between growing and shrinking, and this happens independently of other MT

Question 9

are MT GTPase or ATPases

Answer 9

GTPase

Question 10

which form of tubulin can polymerise

Answer 10

GTP tubulin
and remember GTP hydrolysis to GDP is slow

Question 11

why will MT start to shrink if GTP cap is gone

Answer 11

GTP tubulin bind tighter to each other than GDP, so structure is less stable without the cap
starts to unravel and shrink

Question 12

which protein marks GROWING microtubules and how

Answer 12

EB1
binds inly to GTP bound tubulin

Question 13

what is catastophe

Answer 13

when GTP cap is lost
then MT will depolymerise

Question 14

whats it called when GTP cap reforms and MT starts regrowing

Answer 14

rescue !

Question 15

what natural thing stabilises MT

Answer 15

microtubule asssociated proteins
MAPs

Question 16

what are the 2 neuronal MAPs

Answer 16

Tau
MAP2

Question 17

what synthetic drug is used to stabilise MT

Answer 17

taxol

Question 18

what ‘captures’ MT plus ends to stabilise them

Answer 18

microtubule capping protein

Question 19

2 ways to depolymerise MT experimentally

Answer 19

putting cells on ice
or
drugs that prevent new assembly

Question 20

another name for actin filaments

Answer 20

microfilaments

Question 21

examples of contractile bundles that actin is found in

Answer 21

stress fibres
contractile rings
(and muscle too predominantly)

Question 22

3 examples of non-contractle bundle that actin is found in

Answer 22

microvilli
lamellipodium
filopodia

Question 23

what is actin filaments assembled from and whta kind of structure is it

Answer 23

actin monomers
thin, helical, less complex that MT

Question 24

is actin ATPase or GTPase

Answer 24

ATPase

Question 25

what form of actin will grow the filament

Answer 25

actin bound with ATP

Question 26

what does minus end do in actin

Answer 26

where depolymerisation/shrinkage happens

Question 27

what binds to minus end to prevent depolym in actin

Answer 27

capping proteins

Question 28

what natural molecule stabilises actin filaments, causing the organism that produces this to be poisonous

Answer 28

phalloidin means actin cant grow

Question 29

2 natural molecules that precent acting polymerisation that are produced by fungus/sponge

Answer 29

Cytochalasin Latrunculin

Question 30

what protein binds to actin monomers and prevents it polymerising

Answer 30

thymosin

Question 31

what do nucelating proteins do

Answer 31

promote polymerisation in actin AND microtubules

Question 32

what 2 proteins alter actin filament lenth/dynamics

Answer 32

severing protein - cuts it off, depolymerises capping protein - stops it growin

Question 33

2 proteins that change how actin filaments are organised

Answer 33

cross-linking proteins bundling protein

Question 34

2 prtoeins that control movement along the actin filaments

Answer 34

motor protein side-binding protein