The Cytoskeleton

Question 0

What motor proteins associate with actin?

Answer 0

Myosins

Question 1

What is actin?

Answer 1

Monomeric 4-lobed ATPase, polymerases to form actin filaments which have roles in cell movement and muscle contraction.

Question 2

Which direction do myosin motors move towards?

Answer 2

The plus end.

Question 3

What is tubulin?

Answer 3

Dimeric GTPase, one subunit GTP can be hydrolysed, the other is GTP-locked.

Question 4

What is a MTOC?

Answer 4

Microtubule organising centre, gamma tuRC is an example of this.

Question 5

Where is gamma tuRC found?

Answer 5

In the matrix of the centrosome

Question 6

Why are dyneins important?

Answer 6

They localise the golgi body to the centre of the cell, and are used in vesicle trafficking.

Question 7

What do kinesins bind to?

Answer 7

Proteins on the membrane of membrane-bound organelles or other microtubules.

Question 8

Which proteins do kinesins associate with?

Answer 8

Microtubules (a and B tubulin polymer)

Question 9

How many heads can myosins have?

Answer 9

1 or 2 heads

Question 10

How many heads can kinesins have?

Answer 10

2 only

Question 11

What is the mechanism of myosin movement?

Answer 11

Myosin heads are bound to the actin filament when no ATP is bound. ATP binds, causing the head to detach and subsequent hydrolysis (releasing Pi) causes the head to change its angle. This then releases ADP. The free myosin head can now bind to the actin filament further along.

Question 12

What is the mechanism of kinesin movement?

Answer 12

the ATP bound trailing head is bound to the microtubule, while the ADP bound leading head binds to the microtubule more loosely. The exchange of ADP for ATP in the leading head group causes the flexible hinge region to swing from backwards-orientated to forwards-orientated, moving the back head and simultaneously hydrolysing the bound ATP molecule to form ADP and Pi, which dissociate at the same time.

Question 13

What is K(ON)?

Answer 13

Rate constant of association

rate = k[A][B] for A + B -> AB

Question 14

How do you determine the equilibrium constant of association?

Answer 14

Ka = [AB]/[A][B] or K(ON)/K(OFF)

Question 15

What protein prevents association of actin filaments?

Answer 15

Thymosin

Question 16

Name a nucleator of both actin and of tubulin

Answer 16

Arp2/3 and gamma-TuRC

Question 17

Which is the largest and fastest motor protein?

Answer 17

Dyneins (14um/s)

Question 18

Which motor protein is evolutionarily related to myosin?

Answer 18

Kinesin

Question 19

What direction does myosin move?

Answer 19

Towards barbed (positive) end

Question 20

What is the exception to the myosin movement directionality?

Answer 20

Myosin IV (moves towards pointed end)

Question 21

When does tread milling occur?

Answer 21

Between critical concentrations

Question 22

Which motor proteins are structurally similar to Ras and how?

Answer 22

Myosins and kinesins - have cores which bind ATP (instead of GTP) and couple ATP hydrolysis to the swinging out of a loop which changes affinities for actin/tubulin filaments.