Many key cellular
processes rely on the physical interplay between biological components to
perform functions. The "parts list" in these processes is similar:
Microtubules, semi-rigid tubes of protein, can serve within the cell as
scaffolding, roadways, and a building material for machinery; some proteins serve
as fasteners, binding and releasing other materials; and motor proteins use
chemical energy to push and pull materials along microtubules, or move the
microtubules themselves.
To form the mitotic
spindle, two organelles called centrosomes move into position on opposite sides
of two identical sets of chromosomes massed near the center of the cell. From
each of the centrosomes, a dense network of microtubules is assembled, reaching
toward and around the mass of chromosomes. Some of the microtubules connect to
the chromosomes, while others connect the two centrosomes, forming a cage
around the chromosomes. Ideally, microtubules from each centrosome connect
exclusively with one of each of the chromosomes in the set. Then the
microtubules -- aided by proteins and motor proteins -- begin to shorten and
move, pulling the chromosomes toward the centrosomes, until the two sets have
been separated.
Posted by Dr. Tim Sandle