Cytoskeleton (microtubules) Flashcards Preview

MCBL > Cytoskeleton (microtubules) > Flashcards

Flashcards in Cytoskeleton (microtubules) Deck (51):
1

What is the major goal of microtubules?

organizing

2

What is the microtubule function?

cytoplasmic scaffolding
cells movement

3

What is cytoplasmic scaffolding?

machinery to move organelles within cells and to form mitotic spindle

4

How does microtubules move the cell?

they form cilia and flagella

5

What are the proteins that make up microtubules?

alpha tubulin
beta tubulin

6

What is the makeup of alpha and beta tubulin in cells?

very abundant
2.5% of all protein in non neuronal cells

7

What is the structure of microtubules?

long cylindrical hollow structures composed of tubulin subunits arranged in protofilaments

8

What are the wall of microtubules consist of?

two forms of heterodimers of globular tubulin subunits stacked together

9

How does the heterodimers form protofilaments?

they line up head to tail to form protofilaments
protofilaments show structural polarity

10

How many protofilaments form the wall of the tube?

13 protofilaments

11

Does the final MT show structural polarity?

yes because all protofilaments line up in the same direction

12

What is on each end of the MT?

a plus end
a minus end
each end is functionally and structurally distinct, not a charge

13

Which end polymerize/depolymerize fastest?

plus

14

Which end polymerize/depolymerize slower?

minus
in vivi minus stabilized by other proteins and dont depolymerize

15

What is structural polarity important for in MTs?

polymerization and disassembly

16

What type of protein is tubulin?

a GTP binding protein

17

Which Tubilin is bound to GTP?

the tubulin in the middle of the dimer is always bound to GTP and cannot hydrolyze or exchange

18

When does the GTP bound to a tubulin hydrolyze?

after the dimer attaches to a growing MT

19

When does a tubulin dimer have a high affinity for other GTP tubulin and the plus end of the MT?

When it is bound to GTP

20

When does tubulin has a low affinity other tubulins and MT?

when it is bound with GDP

21

What is a GDP bound tubulin in the middle of the MT strand held in place by?

lateral interactions with the rest of the MT

22

What is the lag phase of MTs?

self aggregation of tubulin dimers. the growth is slow. because small dimers are just as likely to fall apart.

23

What is the elongation phase (growth phase)?

when a oligomer forms and now is stable and growth proceeds very rapidly

24

When does rapid growth continue?

when the rate of addition of subunit removal is equal to subunit addition

25

Why doe the rate of addition slows down?

because free tubulin dimers is limiting so the rate of addition slows while the rate of removal remains the same

26

What does MTs start from in vivo?

initial nucleation ring

27

When does self aggregation proceed at a faster rate in vivo?

presence of a nucleus - a basis for developmental growth

28

Where are the nucleating proteins found?

at the minus end of the MT

29

What is the nucleation ring complex composed of ?

gamma tubulin and accessory proteins

30

How many tubulin monomers form the nucleation ring?

13

31

How many tubulin rings give rise to a MT?

1

32

Where is the nucleation ring located on the MT?

on the static minus end
growing end is the plus end

33

How are the protofilaments formed?

domers add on to the ring at the plus end

34

What is the difference of MT growth in vivo vs in vitro?

Vivo -dimers only add to plus end
Vitro-dimers add to both ends
Both cases plus end is always fastest growth

35

What determines the function and orientation of a microtubule?

Where in the cell it is formed

36

What does nucleation allow for?

rapid and location specific growth of a MT

37

What does nucleation occurs in association with in vivo?

Microtubule organizing centers (MTOC)

38

What are ring complex (nucleation sites) found in association with?

MTOCs

39

What are the MTOCs in animal cells?

centrosomes

40

Where are centrosomes usually located?

near the nucleus

41

What are centrosomes composed of?

pair of perpendicular centrioles surrounded centrosome matrix(pericentriolar material-PMC)

42

What are centrioles composed of?

9 short MT triplets and accessory proteins that are formed from variations of individual Mts

43

What is one triplet composed of?

one complete tubule (w/13 protofilamenst ) connected to two incomplete (<13 protofilament) MTs

44

Which tubule is the inner most complete tubule?

A tubule

45

Which tubule is the incomplete?

B and C tubule

46

Can MT polymerization occur without Centrioles?

yes
centriole function is not known

47

Do plants and fungal cells have centrioles?

No

48

What is the material made of in pericentriolar material?

large number of rings made from tubulin

49

What does tubulin ring serve as?

a nucleation site for microtubule formation

50

Where does microtubules originate and radiate from?

in the centrosome
radiate toward the cell periphery

51

Where does the plus and minus end radiate in the microtubules?

plus end toward plasma membrane
minus end closer to the nucleus

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