8.2 Microtubules & MAPs

Question 1

Dynamic Instability

Answer 1

Cycle of assembly/disassembly occurs randomly in a population of microtubules. Some are growing, some are shrinking at the same time even tho as a whole they might have a constant amount of free polymer and dimer

Question 2

Catastrophe

Answer 2

Accidental loss of the GTP cap on the + end of the growing microtubule. When this occurs, the microtubule will shrink rapidly and depolymerize completely unless it is rescued by some stabilizing factor

Question 3

What structures are responsible for nucleating microtubules in cells?

Answer 3

The Y-tubulin ring complexes on the centrosome. The microtubule starts at the Y-tubulin and it’s + end points away from the centrosome complex. There are many Y-tubulin locations around the centrosome.

Question 4

What is the smallest unit of a microtubule?

Answer 4

A tubulin dimer made up of an alpha and a beta monomer.

Question 5

Protofilament

Answer 5

A series of tubulin heterodimers attached in a line. A microtubule is made up of 13 tubulin protofilaments arranged in a circle around a lumen center.

Question 6

Microtubule assembly and disassembly occurs preferentially at the ____ end.

Answer 6

+ end

Question 7

What proteins transport organelles, chromosomes and other cargo molecules along microtubules?

Answer 7

Dyneins and Kinesins

Question 8

Which tubulin subunits hydrolyzes GTP?

Answer 8

Only the beta subunit hydrolyzes GTP. Although GTP binds to both alpha and beta subunits.

Question 9

Loss of the GTP cap causes ______ .

Answer 9

Conformational change and microtubule disassembly.

Question 10

Microtubules do not typically exhibit ______ .

Answer 10

Treadmilling. They can perform it tho.

Question 11

Centrosomes contain 2 _________.

Answer 11

Centrioles.

Question 12

Microtubule + ends associate with the __________ .

Answer 12

Cell periphery

Question 13

Microtubule - ends associate with the __________ .

Answer 13

Centrosome

Question 14

Plant and fungi centrosomes lack _________ .

Answer 14

Centrioles

Question 15

MAPs

Answer 15

Microtubule associated proteins. Function = regulate stability, distribution and organization of microtubules.

Question 16

Phosphorylation of MAPs causes them ________ .

Answer 16

To fall off microtubules resulting in less stable microtubules.

Question 17

MAP2

Answer 17

Makes loose bundles of microtubules

Question 18

Tau

Answer 18

Microtubule bundling protein = generates closely packed bundles. Highly expressed in neurons and implicated in Alzheimer’s disease.

Question 19

Microtubules are much less stable in ____ cells than in _____ cells.

Answer 19

Motile/Non-motile. Dynamic Instability is regulated differently in motile vs. non-motile cells.

Question 20

Catastrophins

Answer 20

induces microtubule catastrophe.

Question 21

Katanin

Answer 21

cuts microtubules

Question 22

Stathmin

Answer 22

Dephosphorylation of stathmin lowers the effective tubulin concentration and stimulates microtubule turnover.

Question 23

What is the function of EB1 proteins in cells?

Answer 23

EB1 and associated Kar9 associates with GTP-tubular at the growing microtubule + end and helps attachment to the target sites.

Question 24

In cells, dynamic instability typically occurs ________ .

Answer 24

At the + ends

Question 25

For a population of microtubules undergoing dynamic instability, __________ .

Answer 25

Some microtubules will grow at their + end while others will shrink.

Question 26

A growing microtubule has GTP bound to the _________ .

Answer 26

GTP bound to B-tubulin subunits at the + end of the microtubule. Growing microtubules are protected by a GTP-tubulin cap. When GTP hydrolyses to GDP, the GDP tubulin disassembles readily.

Question 27

Dynein

Answer 27

Minus end directed microtubule motor (microtubule dependent ATPase). Involved in chromosome separation, movement of cilia and flagella and direction of membrane bound organelles toward the cell center (golgi, endocytic vesicles)

Question 28

Kinesin

Answer 28

+ end directed microtubule motor (microtubule dependent ATPase)

Question 29

What organelles have kinesins associated with them?

Answer 29

chromosome transportation during mitosis

Question 30

Processiveness

Answer 30

How long something is to continue after starting

Question 31

Which is more processive? Kinesin or Myosin

Answer 31

Kinesin is highly processive. It is less likely to fall off and is good for moving things over long distances in the cell.

Question 32

What microtubule motor protein is involved in chromosome separation?

Answer 32

Dyneins