cytoskeleton; microtubules

Question 1

what are the 4 functions of microtubules?

Answer 1

1. establish internal polarity to movements and structures in interphase cell
2. participate in chromosome segregation during cell division
3. establish polarity during cellular movement
4. produce extracellular movement via beating of cilia and flagella

Question 2

build up structure of a microtubule

Answer 2

tubulin heterodimer; b unit and an a unit
- polymerise > protofilament, many of them joine up
- 13 of them will coil and create a protofilament coil with a lumen in the middle

Question 3

polarity of a microtubule

Answer 3

has a - and a + end, - end faces the nucleus, + end faces to peripheral of the cell.

Question 4

which end does the microtubule grow at?

Answer 4

tubulin subunit addition takes place at the + end

Question 5

process of microtubule growing

Answer 5

tubulin molecule with bound GTP > adds to end of microtubule > addition proceeds fast than GTP hydrolysis to GDP therefore, GTP cap is created

Question 6

what is a GTP cap?

Answer 6

a build up of GTP at the + end of microtubule.
helps to keep the attaching subunits uniform and not lose shape causing catastrophe. catastrophe; loss of the protofilaments binding to eachother and therefore causes shrinkag eof the microtubule

Question 7

process of microtubule shrinkage

Answer 7

protofilaments containing GDP tubulin peel away from microtubule wall > GDP + tubulin released to cytosol = loss of a unit and shortening of the microtubule

Question 8

dynamic instability

Answer 8

• total mass of polymerised tubulin remains constant but individual microtubules are dynamic

Question 9

what is the centrosome?

Answer 9

determines cell polarity, organisation of cell organelles, direction of membrane trafficking and orientation of microtubules. - - primary microtubule nucleation site in most cells

Question 10

centrosome and microtubule growing

Answer 10

• microtubules grow from y-tubulin complexes (nucleating sites) on centrosomes

Question 11

polarity of the microtubule and the centrosome

Answer 11

• end; slow growing, anchored at centrosome in most cells
  + end; fasting growing, usually in the cytoplasm

Question 12

what are the centrosomes known as?

Answer 12

MTOCs; microtubule-organising centers

Question 13

why are microtubules dynamic?

Answer 13

• allow cell to quickly reorganise network when building mitotic spindle
• probe cytoplasm for specific objects & sites on the plasma membrane; search and capture

Question 14

what are MAPs?

Answer 14

microtubule associated proteins
- function as cross bridges connecting microtubules
- can affect microtubule rigidity and assembley rate

Question 15

MAP; stathmin

Answer 15

promotes depolymerization of microtubules and/or preventing polymerization of tubulin heterodimers

Question 16

MAP; kinesin 13

Answer 16

enhances catastrophic disassembly at + end

Question 17

MAP; katanin

Answer 17

severs microtubules

Question 18

MAP; MAP-2

Answer 18

filament bundling and cross-linking

Question 19

MAP; plectin

Answer 19

links to IFs

Question 20

MAP; XMAP215

Answer 20

stabilise + ends and accelerates assembly

Question 21

MAP; +TIPs

Answer 21

remain associated with growing + ends & can link them to other structures such as membranes

Question 22

general roles of MAPs

Answer 22

• prevent/promote cytosolic microtubule depolymerisation
• organise microtubules into bundles or crosslink them to membranes & IFs

Question 23

what are motor proteins?

Answer 23

• enzymes that convert ATP hydrolysis directly into movement along cytoskeletal filaments
• some motors move towards + end, others to - end

Question 24

what do motor proteins do?

Answer 24

carry cargo e.g. organelles, protein complexes, RNA
mediate microtubule sliding