1. Atomic Structure of Tubulin.
(Ribbon and Space Filling Models)

2. Molecular Structure of a Nucleoside Triphosphate
(ATP or GTP)

4. TEM of Self Assembled MTs and MTs Assembled on a Centrosome “template”

5. Microtubules and Motors: MT polymer ratchets and motor proteins.
F ~1-50pN
F ~ 1-10pN

8. Filament Assembly and Force Production.

9. Microtubule Polymer Dynamics
Dynamic Instability.
(Mitchison and Kirschner, 1984).
Flux.
(Margolis and Wilson, 1978; Mitchison, 1989).

10. GTP hydrolysis and Dynamic Instability at Steady State.

11. Microtubule Dynamics in Anaphase A
Metaphase
Anaphase A
Anaphase B
Today, I will talk only about anaphase B, the last step in chromosome segregation, which begins after chromosomes are aligned at the metaphase plate. After all chromosomes have aligned, sister chromatids separate and move to opposite poles during anaphase A. In Drosophila, most of this movement occurs while the pole-pole distance is maintained. After anaphase A is nearly complete, the spindle elongates, thus separating chromosomes further, during anaphase B. This pole-pole separation is linear as can be seen in this graph for the average of several spindles and for an individual spindle.

12. Mechanism of Chromosome Movement.
Kinetochore motility - Pacman versus poleward flux.

13. MT dynamics in Anaphase B
Metaphase
Anaphase A
Anaphase B
Today, I will talk only about anaphase B, the last step in chromosome segregation, which begins after chromosomes are aligned at the metaphase plate. After all chromosomes have aligned, sister chromatids separate and move to opposite poles during anaphase A. In Drosophila, most of this movement occurs while the pole-pole distance is maintained. After anaphase A is nearly complete, the spindle elongates, thus separating chromosomes further, during anaphase B. This pole-pole separation is linear as can be seen in this graph for the average of several spindles and for an individual spindle.

14. Anaphase B Spindle Elongation
The main point of my talk is to explain anaphase B spindle elongation. I will show you that a motor-dependent sliding filament mechanism generates the force to push the poles apart during anaphase B and that poleward flux acts as a switch, depolymerization at the poles has to be turned off, so the motors can be engaged and can pull the poles apart.
Mention old proposals.
1. A motor-dependent sliding filament mechanism generates force to push the poles apart.
2. Poleward flux acts as a regulatory switch.