Chapter 9

Question 1

What three filamentous structures compose the cell’s cytoskeleton?

Answer 1

1. Microtubules
2. Actin filaments
3. Intermediate filaments

Question 2

How are the three different filaments held together?

Answer 2

weak, noncovalent bonds

Question 3

What are the 5 functions of the cytoskeleton?

Answer 3

1. Serve as a scaffold
2. Serve as an internal framework
3. directs the movement of materials and organelles
4. generates force
5. makes up an essential part of the cell division machinery

Question 4

What are microtubules arranged in rows called?

They are a set of globular proteins

Answer 4

protofilaments

13 total

Cross section though a microtubule. Shows 13 subunits

rows are aligned side by side in a circular pattern

Question 5

How are protofilamanets assembled?

The subunit of a microtubule

Answer 5

They are assembled from building blocks that consist of one alpha and beta tubulin

3D structure

longitudinal section of a microtubule

Arranged in linear array along the length of the protofilament, which is asymmetric and polar

Question 6

The plus end is terminated by a row of ________________ and the minus end and is terminated by a row of ____________.

Answer 6

β-tubulin subunits, α-tubulin subunits

Question 7

The α-tubulin subunit has a bound _ _ _ _ _ , which is not hydrolyzed and is nonexchangeable. The β-tubulin subunit has a bound _ _ _ _ _ , which is exchanged for a GTP prior to assembly into a polymer.

Answer 7

GTP, GDP

Question 8

How are the αβ-tubulin heterodimers stacked?

Answer 8

Head-to-tail arrangement

Question 9

Where do microtubules extend outward from?

Answer 9

The nucleus

Microtubules extend from the perinuclear region of the cell in a radial array and curve gradually as they conform to the shape of the cell.

Makes round, flattened shape

Question 10

Treatment of cells with nocodazole or colchicine does what?

Answer 10

promote microtubule disassembly

Question 11

Structures can either move in which two directions?

Answer 11

Anterograde (away from the cell body) and retrograde (to the cell body)

Question 12

What are the three catagories of moleuclar motors?

Answer 12

1. Kinesin
2. Dynein
3. Myosin

Question 13

What energy source do molecular motors use to create mechanical energy?

Answer 13

ATP

Question 14

What are the parts of kinesin molecule?

Answer 14

Two identical heavy and light chains

Also a tetramer

Head binds to the microtubule and the tail binds to the cargo

Question 15

kinesin is a _ _ _ _ _ _ -directed microtubular motor.

Answer 15

Plus end

Question 16

Kinesin has their plus end facing the terminal end of an axion and can help carry what?

Answer 16

transport vesicles toward the synapse

minus ends are facing the cell body

Opposite is true in most cells

Question 17

How big is a kinesin step?

Answer 17

8 nm

And uses 1 ATP molecule via hydrolysis

Question 18

What are the parts of cytoplamic dynein?

Answer 18

Two identical heavy chains and a variety of intermediate and light chains

Large globular force-generating head and microtubule-binding stock

Question 19

Dynein moves in which direction?

cytoplamic dynein

Answer 19

Towards the polymer’s minus end

opposite of most kinesins (except neural)

Question 20

Because cytoplasmic vesicles are seen to move in both directions within an axon, can you conclude that some microtubules are oriented with their plus end facing the axon terminus and others oriented with the opposite polarity? Why or why not?

Answer 20

No, kinase and dynein move in opposite directions. Not needed

Question 21

What are the two plases of assembly of microtubules?

Answer 21

Slow phase of nucleation and a rapid phase of elongation

Question 22

Microtubule-organizing centers (MTOCs) help what?

Answer 22

Nucleation of microtubules

Question 23

What are the roles of MTOCs?

Answer 23

• control number of microtubules
• polarity
• number of protofilaments
• time and location of assembly

Question 24

What is the best studied MTOC?

Answer 24

The centrosome