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

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

Dynamic instability

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

Assembly of microtubules

In animal cells, microtubules

extend outward from the

centrosome.

Mitotic spindle

The role of centrosome is to

initiate microtubule growth.

Structure of centrosome

Centriole Microtubule

Pericentral material

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

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.

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

(Motor domain)

Heavy chains

kinesin

Cargo transport

Cilia and flagella

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.

Movements of microtubules in cilia and flagella

Reorganization of

microtubules during mitosis

Chromosome movement