What is the basic structure of a microtubule?

dimer (beta-tubulin and alpha-tubulin)

both hold GTP

What does beta-tubulin do that alpha tubulin can't?

can hydrolyze GTP

How many protofilaments does one microtubule have?

13 - makes a spiral circle

Where does most growth and shrinkage occur on a microtubule? Why?

on the plus end, because the minus end is anchored in the nucleator

What does rescue microtubules mean?

growth - tubulins added

what does catastrophe mean?

Shrinkage

What is dynamic instability?

switching between catastrophe and rescue (same idea as treadmilling)

activity only on the plus end bc the minus end is anchored

Why do we want dynamic instability?

to be able to take off and take action by growing or shrinking only on ONE END

How do we know when to undergo dynamic instability?

when the rate of GTP hydrolysis is slower than the rate of tubulin addition

What form are dimers added and lost?

added in GTP form (stable)

Lost in the GDP form (less stable)

these changes are done by beta-tubulin only

What is the structure of the microtubules when GTP bound and GDP bound?

GTP - straight

GDP - bent (trying to change conformation)

What are the 2 drugs that destabilize microtubules?

Colchicine and Nocodozole

- favor catastrophe

What is the 1 drug that stabilizes microtubules?

Taxol (cancer therapy)

Why would it be bad if cells cant undergo catastrophe on the plus end?

inhibits cell division - spindle shortens MT by pulling during anaphase, if catastrophe cant occur no depolymerization

What are microtubules nucleated by?

gamma TuRC (ring complex)

what end of the microtubule does nucleation occur?

on the minus end

How many gamma TuSC does it take to form a ring complex?

7

What is the gamma tubulin ration with gamma TuSC and gamma TuRC?

2 gamma tubulin for every 1 gamma TuSC

7 gamma TuSC for every 1 gamma TuRC

what is the total number of protofilaments created?

14 but we 13 used because one is stacked on top of each other to create the spiral

What region does the gamma TuRC perform nucleation?

MTOC

What is the MTOC for animals?

centrosome

What is the centrosome structure?

has 2 centrioles inside pericentriolar material (jelly) with gamma tubulin rings surrounding (nucleating sites)

What is the major function of microtubules

determine position of the internal organelles

centrosome radiates MT in all directions so it can find the center of the cell (puts nucleus in middle and rest of organelles follow position)

acts as a highway for transport vesicles to move from one organelle to another

How many triplets are centrioles made out of?

9

one has 13 protofilaments and 2 other couple on and share

What are the functions of the different lengths of arms on a microtubule?

MAP2 - long arms (more stable)- makes sure nothing can touch MT, can only get as close as the length of the arm

tau - short arms (less stable) short binding - MT closer to each other

why is there a difference between the microtubule protein arms

MAP - determines spacing - farther (stable binding)

tau - closer spacing short binding

What are the 2 specific MAPs proteins that affect the rate of polymeriation at the plus end?

Kinesin-13 = favors catastrophe (destabilization - peels off tubulin dimers)

XMAP215 = favors rescue (can pick up dimers and bring them to the plus end to be added)

What is the tubulin sequestering proteins and its function?

stathmin - binds tubulin dimer and keeps it away from the plus end to be added (stops the growth of the plus end)

What is the microtubule severing protein?

katanin - cuts off and chops MT into pieces (can be used to form the spindle in cell division)

What are the 2 motor proteins for MT and their function?

kinesin - walk toward the plus end

dysein - walk toward the minus end

How does cAMP impact the direction of movement for the kinesin?

high levels of cAMP activates kinesins to move pigments toward the plus end of the MT to periphery

Anteriograde movement through the secretory pathway

How does cAMP impact the direction of movement for the dynein?

low levels of cAMP moves pigments to the minus end of the MT (all clump together in the middle)

Retrograde movement

What is the mechanism for kinesins?

1. hold cargo and head binds to B-tubulins on the MT surface (back head ATP front head ADP)

2. the back head is hydrolyzed, releasing inorganic phosphate

3. front head trades and bind ATP tightly and back head swings forward

4. REPEAT

How is the dyneins binded to MT?

MT bound to dynein bound to dynactin complex to the vesicle (cargo)

REQUIRES ADAPTER COMPLEX (dynactin)

cilia

movement of fluid, sweeping motion, stays static

where could cilia be found

in lungs (gets rid of fluid and dust), trachea, inner ear (perceive sound)

flagella

cell movement, uses locomotion, like a sperm cell - swims

What are cilia and flagella built out of?

have 9 fold symmetry (9 doublets) with 2 single doublets

9+2 arrangment

What causes the flagella to have a whipping movement?

cross-linking proteins, limit sliding of MT doublets so instead of sliding up the MT bend on one side to another which creates a whipping movement

What causes the flagella to have a sliding movement?

dynein on MT doublets walk along each other either up or down which creates a sliding movement

one side is fixed, the other is dynamic