BI203 Lecture 19: Cytoskeleton - Microtubules

Question 1

____ are rigid hollow rods made up of tubulin.

Answer 1

microtubules

Question 2

Microtubules are rigid hollow rods made up of ____.

Answer 2

tubulin

Question 3

Microtubules are dynamic structures that undergo continual assembly and disassembly.
They function in cell ____ and determining cell ____.

Answer 3

movements, shape

Question 4

____ - Composed of dimers of a- and b-tubulin that polymerize, with 13 protofilaments each.

Answer 4

Microtubules

Question 5

Microtubules - Composed of dimers of ____ and ____ that polymerize, with 13 protofilaments each.

Answer 5

a-tubulin, b-tubulin

Question 6

Microtubules - Composed of dimers of a- and b-tubulin that polymerize, with ____ ____ each.

Answer 6

13 protofilaments

Question 7

Alpha and Beta tubulin dimers polymerize to form microtubules: 13 protofilaments around a ____ core.

Answer 7

hollow

Question 8

____ are head-to-tail arrays of tubulin dimers arranged in parallel. Microtubules have polarity (plus and minus ends), which determines direction of movement.

Answer 8

Protofilaments

Question 9

____ in the centrosome helps to initiate microtubule assembly.

Answer 9

y-tubulin

Question 10

How do microtubules polymerize?

Tubulin dimers with ____ ____ associate with the growing plus end while in a flat sheet.

Answer 10

GTP-bound b-tubulin

Question 11

How do microtubules polymerize?

Tubulin dimers with GTP-bound b-tubulin associate with the growing ____ ____ while in a ____ ____.

Answer 11

plus end, flat sheet

Question 12

The flat sheet then zips up in to the mature microtubule just behind the region of growth.
The GTP-bound b-tubulin is then ____ to GDP-tubulin, which are less stable and lead to dissociation at the ____ ____.

Answer 12

hydrolyzed, minus end

Question 13

In microtubules stabilized at the minus end, rapid GTP hydrolysis results in ____ ____: Alternating between cycles of growth and shrinkage.

Answer 13

dynamic instability

Question 14

As long as new ____ ____ ____ are added more rapidly than GTP is hydrolyzed, a GTP cap remains at the plus end and microtubule growth continues.

Answer 14

GTP-bound tubulin dimers

Question 15

If GTP is hydrolyzed more rapidly than new subunits are added, ____ ____ at the plus end of the microtubule leads to disassembly and shrinkage.

Answer 15

GDP-bound tubulin

Question 16

____ ____ (MAPs) regulate the dynamic behavior of microtubules.

Answer 16

Microtubule-associated proteins (MAPs)

Question 17

Minus ends are stabilized by proteins that ____ depolymerization.

Answer 17

prevent

Question 18

Growth or shrinkage of plus ends is regulated by ____ ____.

Answer 18

Microtubule-associated proteins (MAPs)

Question 19

____ proteins rescue microtubules from catastrophe by stopping disassembly and restarting growth.

Answer 19

CLASP

Question 20

Other MAPs bind to the plus ends and mediate attachment of microtubules to other structures (i.e. ____ ____ or ____ ____), and regulate microtubule dynamics.

Answer 20

plasma membrane, endoplasmic reticulum

Question 21

____ turnover of microtubules allows for remodeling of the cytoskeleton that occurs during mitosis.

Answer 21

rapid

Question 22

Drugs such as ____ and ____ that affect microtubule assembly are useful as experimental tools and in cancer treatments.

Answer 22

colchicine, colcemid

Question 23

____ and ____ are used in cancer chemotherapy because they inhibit microtubule polymerization and thus affect rapidly dividing cells.

Answer 23

Vincristine, vinblastine

Question 24

____ stabilizes microtubules, which also blocks cell division. (see relevant Discussion material).

Answer 24

Taxol

Question 25

The ____ ends of microtubules are anchored at the centrosome.

Answer 25

minus

Question 26

In animal cells, most microtubules extend outward from the ____. During mitosis, they extend outward from duplicated centrosomes to form the ____ ____.

Answer 26

centrosome, mitotic spindle

Question 27

The mitotic spindle controls the separation and distribution of chromosomes to daughter cells during mitosis. The centrosome is a ____ ____.

Answer 27

microtubule-organizing center

Question 28

Fungi use ____ ____ ____ instead of mitotic spindles (such as in animal cells) during mitosis.

Answer 28

spindle pole bodies

Question 29

Plant cells do ____ have centrosomes; microtubules instead form a(n) ____ underlying the plasma membrane and function in synthesis of plant cell walls.

Answer 29

NOT, array

Question 30

Cells were treated with colcemid, a tubulin-binding anti-cancer drug that inhibits polymerization for 30 min. The cells were then allowed to recover to show nascent microtubules at the centrosome, initiated by the ____ ____ ____.

Answer 30

y-tubulin ring complex

Question 31

The centrosome of most animal cells contain a pair of ____, oriented perpendicular to each other and surrounded by the pericentriolar material.

Answer 31

centrioles

Question 32

The centrosome of most animal cells contain a pair of centrioles, oriented perpendicular to each other and surrounded by the ____ ____.

Answer 32

pericentriolar material

Question 33

γ-tubulin associates with other proteins in a ring-shaped structure called the ____ ____ ____. This complex is thought to bypass the rate-limiting nucleation step, speeding up microtubule growth.

Answer 33

y-tubulin ring complex

Question 34

Centrioles are cylindrical, containing ____ ____ of microtubules.

Answer 34

nine triplets

Question 35

In ____, all microtubules are oriented with their plus ends toward the tip. Associated with the MAP: tau.

Answer 35

axons

Question 36

In ____, microtubules are organized in both directions (plus and minus ends at tip). Associated with the MAP: MAP2.

Answer 36

dendrites

Question 37

In neurons, microtubules terminate in the ____ and not in the centrosome.

Answer 37

cytoplasm

Question 38

Different microtubule-associated proteins (____ in axons, ____ in dendrites) cap the ends of MT and stabilize by binding along their length.

Answer 38

tau, MAP2

Question 39

Microtubule stability is regulated by post-translational modification of tubulin by ____, ____ etc. These modifications affect microtubule behavior by providing ____ for binding of specific MAPs.

Answer 39

phosphorylation, acetylation, sites

Question 40

The centrosome is duplicated during ____.

Answer 40

interphase

Question 41

During ____, the centrosomes migrate to form the two poles of the mitotic spindle.

Answer 41

prophase

Question 42

As the cell enters mitosis, the rate of microtubule disassembly increases, resulting in ____ of microtubules. But the number of microtubules emanating from the two centrosomes ____.

Answer 42

shrinkage, increases