8.2 Microtubules & MAPs Flashcards

1
Q

Dynamic Instability

A

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

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2
Q

Catastrophe

A

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

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3
Q

What structures are responsible for nucleating microtubules in cells?

A

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.

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4
Q

What is the smallest unit of a microtubule?

A

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

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5
Q

Protofilament

A

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.

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6
Q

Microtubule assembly and disassembly occurs preferentially at the ____ end.

A

+ end

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7
Q

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

A

Dyneins and Kinesins

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8
Q

Which tubulin subunits hydrolyzes GTP?

A

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

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9
Q

Loss of the GTP cap causes ______ .

A

Conformational change and microtubule disassembly.

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10
Q

Microtubules do not typically exhibit ______ .

A

Treadmilling. They can perform it tho.

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11
Q

Centrosomes contain 2 _________.

A

Centrioles.

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12
Q

Microtubule + ends associate with the __________ .

A

Cell periphery

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13
Q

Microtubule - ends associate with the __________ .

A

Centrosome

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14
Q

Plant and fungi centrosomes lack _________ .

A

Centrioles

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15
Q

MAPs

A

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

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16
Q

Phosphorylation of MAPs causes them ________ .

A

To fall off microtubules resulting in less stable microtubules.

17
Q

MAP2

A

Makes loose bundles of microtubules

18
Q

Tau

A

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

19
Q

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

A

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

20
Q

Catastrophins

A

induces microtubule catastrophe.

21
Q

Katanin

A

cuts microtubules

22
Q

Stathmin

A

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

23
Q

What is the function of EB1 proteins in cells?

A

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

24
Q

In cells, dynamic instability typically occurs ________ .

A

At the + ends

25
Q

For a population of microtubules undergoing dynamic instability, __________ .

A

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

26
Q

A growing microtubule has GTP bound to the _________ .

A

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.

27
Q

Dynein

A

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)

28
Q

Kinesin

A

+ end directed microtubule motor (microtubule dependent ATPase)

29
Q

What organelles have kinesins associated with them?

A

chromosome transportation during mitosis

30
Q

Processiveness

A

How long something is to continue after starting

31
Q

Which is more processive? Kinesin or Myosin

A

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

32
Q

What microtubule motor protein is involved in chromosome separation?

A

Dyneins