This document discusses microtubules and their role in cell movement. It describes how vincristine and vinblastine inhibit microtubule polymerization and cell division in rapidly dividing cells. It also discusses dynamic instability in microtubule growth and shrinkage cycles. The document outlines how microtubules extend from the centrosome in animal cells and form the mitotic spindle. It describes the structure of the centrosome and centrioles, and how gamma-tubulin nucleates microtubule assembly. Finally, it briefly summarizes microtubule organization in cells and their role in processes like cargo transport, cilia/flagella movement, and chromosome movement during mitosis.

1. Molecular & Cell Biology
S. Rahgozar,PhD
University of Isfahan
Faculty of Science
6. Cytoskeleton and Cell Movement
6.3. Microtubules and Microtubule Motors
1392-93

3. Treadmiling and the role of GTP in microtubule polymerization
Vincristine and Vinblastine selectively inhibit rapidly dividing cells
by binding β-tubulin and inhibiting microtubule polymerization.
Colchicine and Colcemid have the same effect but do not act
selectively

4. Dynamic instability
The alteration between cycles of growth and shrinkage is called dynamic instability

5. Assembly of microtubules
In animal cells, microtubules
extend outward from the
centrosome.
Mitotic spindle
The role of centrosome is to
initiate microtubule growth.

6. Structure of centrosome
CentrioleMicrotubule
Pericentral material

7. Structure of centriole. Centrioles are highly polar structures
with a cartwheel protein structure at one end and several types of processes
extending from the other end.
γ-tubulin, in association of several other proteins nucleates assembly of
microtubules. It is also found in the cytosol, and in plants, at the periphery of the
nucleus.
Centrin :
a Ca2+ binding
protein related
to calmodulin

8. Organization of Microtubules
 Microtubule stability is modulated by
 Stable microtubules
determine polarity
Organization of microtubules in nerve cells
o Extensive post-translational modification of tubulin
o Interaction of microtubules with
microtubule-associated
proteins (MAPs). MAPs
may cap the ends, sever
or track growing microtu-
bules toward specific
cellular locations.

9.  Cytoplasmic Dynein
Heavy chains
Microtubule Motors and Movements
(Motor domain)
o Heavy protein
2000 kd (HC:500 kd)
o moves along with
dynactin to move
cargoes over long
distances along the
microtubules

10. (Motor domain)
Heavy chains
 kinesin

12. Cargo transport

13. Cilia and flagella

14. The minus ends of the microtubules of cilia and flagella are anchored
in a basal body, which is similar in structure to a centriole and
contains nine triplets of microtubules.

15.  Movements of microtubules in cilia and flagella

16. Reorganization of
microtubules during mitosis

18. Chromosome movement