Microtubules

Question 1

General functions of microtubules

Answer 1

Transport

Org. Of organelles

Vesicle movement

Secreting proteins

Supporting structural proteins

Question 2

The repeating monomers of mts

Answer 2

Alpha-beta tubulin

Alpha = will only bind GTP

Beta = can hydrolyze GTP —> GDP so it can bind both

Dimerization is spontaneous

Question 3

Protofilament

Answer 3

Precursor…arrangement of linear repeats of alpha/beta dimers: its wrapped around in a hollow tube that has strong interactions

They align to form a microtubule ring

Question 4

Polarity

Answer 4

(-) end = alpha-tubulin cap

(+) end = beta cap

Question 5

Where do you see

Singlet? Doublets? Triplets?

Answer 5

Singlet = interphase, mitotic microtubules

Doublet = cilia and flagella (mt movement)

Triplet = structural mts…seen in basal bodies and centrioles

Question 6

If you increase the concentration of the monomers —>

Answer 6

Dimer formation will increase

Question 7

Once you hit the critical concentration

Answer 7

The dimer formation will level off…

Question 8

The CC depends on what…

Answer 8

Whether or not you want to make mts…

You’ll get growth with appropriate concentration

Question 9

Will the - or + side of the mt have a higher CC?

Answer 9

The - side will…therefore the assembly is more likely to occur at the + end and more rapidly

Think of the + end as the polymerizing end and - end ast the depolymerizing

Question 10

Above the CC…GTP bound dimers are

Answer 10

Added creating a GTP cap that stabilize the positive end

Question 11

Below the CC, the GTP will

Answer 11

Hydrolyze —> GDP…and create a GDP cap at the positive end

Which will become destabilized

Question 12

Catastrophe

Answer 12

The unstable GDP cap formation and subsequent depolymerization

This can be relieved by adding GTP bound dimers

Question 13

1. If [heterodimer] < CC

Then?

Answer 13

MT depolymerizes

Question 14

If [heterodimer] > CC

Then

Answer 14

MT polymerizes

Question 15

CC+ < [heterodimer] < CC-

Answer 15

Treadmilling effect

Question 16

What are the 2 conditions that affect the MT stability

Answer 16

1. Dimer pool conc.

2. GTP/GDP status of beta-tubulin

Question 17

MT stabilizing proteins (MAPs)

Answer 17

Has a (+) end that binds with the (-) charged MT

—> neutralizes it

This stabilizes the spatial arrangement of neighboring MTs

Has an acidic domain that maintains distance between neighboring MTs

Question 18

Phosphorylation effect on MAPs

Answer 18

Adds (-) charge to inactivate MAP

—> destabilizes MTs

Question 19

Kinesin-13

Answer 19

Bends +/- ends of MT into catastrophe and binds to dimers

Lowers [dimer] —> decrease polymerization

Question 20

Stathmin

Answer 20

Binds two dimers and bends similarly to kinesin

Enhances GTP —> GDP

Depolymerization

Question 21

Katanin

Answer 21

Breaking the MTs

This exposes GDP caps in the middle of MTs and creates several GDP caps —> catastrophe

Rapid degradation for (G2 —> mitosis transition) and (end of mitosis —> G1 transtion) to reorganize the cell

Question 22

Colchicine (drug)

Answer 22

Lowers [dimer] to below CC… by binding them

—> catastrophe

(Used to reduce WBCs migration in gout)

Question 23

Vinblastine (drug)

Answer 23

Destabilizing drug

Lung, breast, and teste cancers

Question 24

Podophyllotoxin (drug)

Answer 24

Destabilizing

Lung and genital tumors, genital warts

Question 25

Nocodazole

Answer 25

Prevents spindle assembly Used in labs mainly

Question 26

Taxol

Answer 26

Stabilizing drug**** Inhibits mitosis Breast and ovarian cancers

Question 27

Main cause of Alzheimers?

Answer 27

Hyperphosphorylation of MAPs —> destabilizes the MTs —> formation of tangles

Question 28

Role of Pin1 in Alzheimers treatment/prevention

Answer 28

Prevents the formation of the cisProline in the repeat sequence in the AB42 plaques and Tau tangles... Makes it transProline —> prevents the phosphorylated state from being maintained (i.e. no hyperphosphorylation)

Question 29

MT org. Centers (MTOC) for... 1. Interphase 2. Mitosis 3. Axon 4. Cilia and flagella

Answer 29

1. Centrosome 2. Spindle poles 3. MTOC 4. Basal bodes

Question 30

Role of MTOCs

Answer 30

Anchor the (-) end of the MTs Functions to start polymerization of MTs

Question 31

Kinesin motor proteins

Answer 31

Anterograde movements Cargo (vesicles or organelles): (-) —> (+) The kinesin tail binds to the cargo... Two motor head domains bind to beta-tubulin...which walk along the MTs Each step requires ATP hydrolysis

Question 32

Dynein motor proteins

Answer 32

Retrograde movement Cargo (+) —> (-) Tail of dyenin binds to cargo Stalk binds to MTs Head has ATPase...when hydrolyzes ATP —> head changes conformation —> results in movement of stalk = POWER STROKE

Question 33

Exocytosis

Answer 33

Glandular cells Secretory vesicle moved using KINESIN At the end of the MT...move along the actin cytoskeleton using the myosin motors to reach the plasma membrane and release its products

Question 34

Endocytosis

Answer 34

Endosomes are transported to their intracellular destination along MTs using Dynein motor proteins

Question 35

Cilia and flagella use which motor proteins

Answer 35

Dynein (arms)

Question 36

Interphase (centrosome)

Answer 36

Centrosome is duplicated along with the DNA

Question 37

Mitotic MTs

Answer 37

Aster Kinetochores Polar

Question 38

Aster

Answer 38

Form spindle poles toward the cell cortex (away from metaphase plate) Orient the spindle poles (MTOC/centrosome) to the axis on which the cell will divide

Question 39

Kinetochore

Answer 39

MTs Attache spindle pole to centromere of chromosome

Question 40

Polar

Answer 40

MTs Used in prometaphase and late anaphase (anaphase B) As well as participating in orientation of the central spindle

Question 41

Prophase

Answer 41

Interphase MTs break down and are replaced by mitotic MTs and chromosomes condense 1. Asters form 2. Dynein proteins of aster —> move toward the (-) end of MTs —> pulling the spindle poles to the opposite sides of the nucleus 3. .at the same time...kinesin motor proteins that are attached as cargo to a polar MT —> move toward the (+) end of the opposite polar MT “Pushing forces in the overlap zone” + “pulling forces on asters” —> spindle poles moving apart

Question 42

Prometaphase

Answer 42

Nuclear envelope breaks down Kinetochore MT and polar MTs are present and reach toward the central spindle region Kinesin motor proteins move toward the (+) end of the MTs —> polar MTs push the duplicated centrosomes apart

Question 43

Metaphase

Answer 43

Chromosomes are aligned at the metaphase plate In order for this to happen...the kinetochores need to treadmill —> elongation = kinesin which holds onto the chromosome and amoves towards the (+) end of the MTs...this pushes the chromosome to center —> shortening = kinesin-13 disassembles MT...and dynenin moves toward the (-) end of the MT ...pulling the chromosome to the center

Question 44

Anaphase

Answer 44

Begins once all chromosomes are aligned at the palte Cohesin = protein that holds the sister chromatids together at the cetromere breaks down...this allows the sisters to separate

Question 45

Anaphase A

Answer 45

Kinetochore MTs shorten and disassemble...pulls chromosomes to the poles Done by kinesin-13 at both +/- ends

Question 46

Anaphase B

Answer 46

Polar MTs using kinesin motor proteins to move the two poles further apart (spindle pole separation)...bring the chromosomes with them... Dynein of aster MTs move towards the (-) end of the aster MTs... Togehter these processes result in the spindle pole separation and chromatid movement to the opposite sides of the cell

Question 47

Telophase

Answer 47

Nuclear envelope re-forms and a contractile ring made of myosin forms in the center...