Ctb 4: Microtubules

Front 1

Describe the structure of microtubules

Back 1

hollow cylinders with a 25nm outer diameter, they are composed of alpha and beta tubluin which form heterodimers that arrange as protofilaments. 13 protofilaments self-assemble to form a microtubule

Front 2

Desribe microtubule treadmilling

Back 2

occurs under equilibrium conditions in vitro, heterodimers pass from the plus end of the MT and fall of the minus end but the net length does not change

Front 3

Describe the role of GTP in microtubule polymerization and how it contributes to dynamic instability

Back 3

1. Polymerization at the plus end requires bound GTP which is hydrolyzed to GDP. 2. Dimeers are added most efficiently to an end capped with GTP. 3. WHEN THE RATE OF ADDITION OF DIMERS EXCCEDS THE RATE OF GTP HYDROLYSIS, A GTP CAP FORMS AND STABLIZES THE MOLECULE 4.When addition of dimers slows down, the GTP cap is lost and the MT depolymerizes

Front 4

on which end of the microtuble is assembly favored

Back 4

the plus end with GTP bound

Front 5

Describe the orientation of the MT's within the bipolar mitotic spindle

Back 5

The minus end of the MT is adjacent to the MTOC (centrosome), the plus ends are located at the chromosome kinetochores and the distal end of the astor MT's

Front 6

Anti-cancer drugs such as taxol and vinvblastine target microtubules. What is the mechanism behind these drugs?

Back 6

Taxol stabilizes microtubules and prevents depolarization at the end to mitosis, vinblastine prevents polymerization and the mitotic spindle can't assemble

Front 7

Give two examples of MTOC's, desribe their structure and role

Back 7

1. Centrioles within the centrosome 2.Centrioles within the basal body from which cilia extend, each of therse structures consist of triplet microtubuels that orient perpenducularly and are radially symmetric. they are very stable and do not show dynamic instability. This is also the site o fthe gamma tubulin ring complex that caps the - end of MTs at the MTOC to prevent disassembly

Front 8

What is the role of gamma tubulin in MT structure and fxn

Back 8

gamma tubulin is part of the multi-protein complex called the gamma tubulin ring complex. The complex is invovled in initiation of polymerization of MT's at MTOC's. The gamma tubulin ring complex caps the minus end of the MT and prevents disassembly

Front 9

Describe the structure and function of the axoneme

Back 9

The axoneme is the cytoskeletal component of the cilium or flagellum it has a 9+2 pattern of MT's; a central pair and 9 outer doublets. The axoneme arises from the basal body that has a cross linked array of 0 triplet microtubles. The basal body is the MTOC for the cilium/ flagellum

Front 10

Describe ciliary bending in terms of MT based motility. What is the motor? Energy?

Back 10

The motor is dynein (plus to minus) and it causes relative sliding between microtubules in the axoneme. ATP hydrolysis provides the energy for movement.

Front 11

In which direction do each of the microtubule motors move?

Back 11

Dynein moves plus to minus), kinesin moves from minus to plus (hint: a k looks like a + sign, kinesin moves to plus)

Front 12

Describe the basic structure of kinesin and the mechanism by which it moves along a MT

Back 12

Kinesin has two heads which function as ATPass as well as a neck linker and a tail for the organelle. Kinesin binds the MT in the ADP which is then released for ATP. This leads to a conformational change which throws the ADP bound head fowrad. The ATP on the back head is hydrolyed to ADP and the ADP on the front heat is exchanged for ATP. This resets the cycle.

Front 13

Describe the orientation of MTs in axons. Which motors mediate transport to differnet parts of the cell?

Back 13

The minus ends are located at the celbody and the plus ends are located at the synpase. Transport toward the synpase (anterograde) is mediate by kinesin while transport towrad the cell body (retrograde) is mediated by dynein.

Front 14

Which motor would be used if a substances was being trasnported from the cell body to the synapse of a neuron

Back 14

Kinesin. The MT's of the axon have their minus end at the cell body and plus end at the synapse. Kinesin moves from minus to plus or from cell body to synapse.

Front 15

Which motor would be used if a substances was being trasnported from the synapse to the cell body of a neuron

Back 15

Dynein. The MT's of the axon have their minus end at the cell body and the plus end at the synapse. Dynein moves from plus end to minus end or from synapse to cell body.

Front 16

Describe the role of microtubule based motors in mitosis

Back 16

The motors are directed in such away that they create pushing and pulling forces. Pushing forces in the overlap zone and pulling foreces on asters create create the movement necessary for cell separation.