Cytoskeleton-MT

Question 1

Cytoskeleton role

Answer 1

1- structural support
2- movement of material
3- force generation for movements
4- framework for organelles
5- cell division

Question 2

Structurally moch of cell polarity is due to

Answer 2

Cytoskeleton

Question 3

Cytoskeleton is —— structure
Capable of reorganizing quickly

Answer 3

Dynamic

Question 4

MT are —— component of cytoskeletal cell

Answer 4

Largest

Question 5

MT two types

Answer 5

1- cytoplasmic MT: pervade cytosol
— maintaining axons
—formation mitotic spindles
—movement vesicles
—maintain/alter cell shape
2- axonemal MT
— structures specialized for movement: cilia/flagella/basal bodies

Question 6

MT protein buildings are

Answer 6

Tubulin heterodimers:
One alpha tubulin
One betta tubulin
Bind non covalently to form ab-heterodimer

Question 7

Protofilaments

Answer 7

MT are straight, hollow cylinders
Having 13 longitudinal arrays of polymers (ab-heterodimer)

Question 8

Alpha and betta subunits have —— structure but —— identity

Answer 8

Similar 3D structures
40% amino acid

Question 9

Each subunit has

Answer 9

N-terminal GTP binding domain
Central domain
C-terminal domain interacting with MAP

Question 10

All dimers in MT oriented in ——

Answer 10

Same way

Question 11

Because of dimer orientation

Answer 11

Protofilaments have an inherent polarity
Two end differ chemically and structurally
+ end
- end

Question 12

Cytoplasmic MT are —— tubes

Answer 12

Simple (single tubes)

Question 13

Axonemal MT are ——

Answer 13

Doublet or triplet MTs
One 13-protofilament tubule (A)
Additional incomplete rings (B/C) of 10-11-Protofilaments

Question 14

Doublet MT can be found in —

Answer 14

Cilia and flagella

Question 15

Triplets can be found in

Answer 15

Basal bodies and centrioles

Question 16

Reversible polymerization of tubulin dimer can only ocuur in presence of

Answer 16

GTP ang Mg

Question 17

Nucleation

Answer 17

Dimers aggregate into oligomers which serve as nuclei
MT grow is slow

Question 18

Elongation

Answer 18

Addition of more subunits at either end
Much faster phase

Question 19

Plateau phase

Answer 19

When concentration of tubulin becomes limiting. Assembly is balanced by disassembly

Question 20

MT assembly depends on

Answer 20

Concentration of tubulin dimers

Question 21

Concentration that MT assembly is balanced by disassembly is

Answer 21

Critical concentration

Question 22

Higher than C(c)

Answer 22

MT grow

Question 23

Lower than C(c)

Answer 23

MT disassemble

Question 24

Addition of tubulin dimers happen

Answer 24

More quickly at plus end

Question 25

Treadmilling

Answer 25

Addition of subunits at plus end Removal from the minus end Higher tubulin conc. Than C(c) in plus end and lowe tubulin conc. than C(c) in minus end

Question 26

Treadmilling occurs if

Answer 26

Tubulin conc. Is higher than plus end C(c) but lower than minus end C(c)

Question 27

If tubulin conc. Is higher than both C(c)

Answer 27

MT will grow from both side

Question 28

If MT conc. Is less than both C(c)

Answer 28

MT will shrink from both side

Question 29

Both alpha and betta tubulin in tubulin heterodimer binds ——

Answer 29

GTP (Doesn’t let them to shrink)

Question 30

Betta subunit will ——— after heterodimer is added to MT

Answer 30

Hydrolyzed GTP to GDP

Question 31

—— is needed to promote heterodimer

Answer 31

GTP

Question 32

—— is not required for MT assembly

Answer 32

Hydrolysis (Happen after assembly)

Question 33

Dynamic instability model

Answer 33

Polymerization at the plus end and shrinking in minus end

Question 34

Growing MT have —— and shrinking MT have

Answer 34

GTP at plus end GDP at minus end

Question 35

—— prevent subunit removal

Answer 35

GTP cap at plus end

Question 36

When tubukin conc. Is high

Answer 36

GTP-tubulin is added to MT faster than GTP can be hydrolyzed, GTP cap stabilize the MT tip and promote further growth

Question 37

Low tubulin conc.

Answer 37

Rate of growth decrease allowing GtP hydrolysis to catch up

Question 38

Hydrolysis of GTP will

Answer 38

Change the conformation of subunit Force protofilament in curved shape that is less able to pack into MT wall

Question 39

Gtp-bound betta tubulin —— MT tip

Answer 39

Stabilize

Question 40

Gdp-bound betta tubulin —— mt tip

Answer 40

Destabilize

Question 41

MT originate from

Answer 41

MTOC ( micro tubule organizing center)

Question 42

Mtoc serve as

Answer 42

Site of MT assembly and anchor for minus end

Question 43

During interphase many cell have and MTOC called

Answer 43

Centrosome

Question 44

In animal cells, centrosome is associated with

Answer 44

Two centrioles

Question 45

Centriole structure

Answer 45

-Centriole wall: 9 sets of triplet MT -Oriented at right angle -Involved in basal body formation -Cell without centrioles have poorly organized mitotic spindles

Question 46

How MTOC speed up the nucleation?

Answer 46

Centrosome have large ring shaped y-tubulin ring complexes (y-TuRC) which nucleate the assembly of MT away from centrosome

Question 47

By y-TuRC effect ——

Answer 47

Only plus end extends but C(c) is still important

Question 48

MT polarity in non-diving cell

Answer 48

MT orientation may vary with cell function

Question 49

MT polarity in dividing cell

Answer 49

High MT nucleating activity during prophase and metaphase (spindle forming)

Question 50

——— regulate the assembly and structure of MT

Answer 50

Microtubule-binding proteins

Question 51

MT-binding proteins:

Answer 51

1- some MT-binding proteins use ATP to drive vesicle or organelle transport 2- MT-stabilizing proteins 3- MT-Destabilizing proteins 4- Plus end tubulin interacting proteins (+-TIP)

Question 52

MT-stabilizing proteins

Answer 52

Microtubule associated proteins (MAP) Bind at regular intervals along MT wall **Tau** cause MT to form tight bundles to axon **MAP2** promote formation of looser bundles in dendrite

Question 53

MAP binding

Answer 53

One region bind MT wall and another part extend at right angle to MT to allow interaction with other proteins

Question 54

Length of extended arm will

Answer 54

Contols spacing of MT in bundle

Question 55

MT are unstable to-remain intact for long periods and will depolarize unless ——

Answer 55

They stabilized in some way +-TIP can stabilize by capturing the plus end and protecting from catastrophic subunit loss

Question 56

+-TIP kind

Answer 56

EB1 association with GTP-tubulin stabilize MT

Question 57

MT-destabilizing Protein

Answer 57

Promote depolarization **Stathmin/Op18** bind to tubulin heterodimer and prevent polymerization **catastrophins(kinesins)** act at end of MT, promoting peeling of subunits from emd **katasins** severe MTs