Question

If fine glass needles are used to manipulate a chromosome inside a living cell during early M phase, it is possible to trick the kinetochores on the two sister chromatids into attaching to the same spindle pole. This arrangement is normally unstable, but the attachments can be stabilized if the needle is used to gently pull the chromosomes so that the mictotubules attached to both kinetochores (via the same spindle pole) are under tension. What does this suggest to you about the mechanism by which kinetochores normally become attached and stay atached to microtubules from opposite spindle poles? Is this finding consistent with the possibility that a kentochore is programmed to attach to mictotubules from a particular spindle pole? Explain your answer.

Answer 1

During the synthesis phase (S phase) in the cell cycle, the centrosome starts to duplicate and as the mitotic phase begins, both centrosomes separate to establish the mitotic spindle.In this way, the spindle in a mitotic cell has two poles emanating microtubules.

Microtubules are long proteic filaments that are fixed at the end of the centrosome, and contains a growing-shrinking end that explores the center of the cell. During this searching process, a microtubule may encounter and capture a chromosome through the kinetochore.

Chromosomes have two kinetochores associated back-to-back (one on each sister chromatid). When one of them gets attached to the microtubules from one of the cellular poles, the kinetochore on the sister chromatid becomes exposed to the opposed pole. This results in the second kinetochore getting attached to the microtubules emanating from the opposite pole.

When just one microtubule is anchored to one kinetochore, it starts a rapid movement of the associated chromosome towards the pole generating that microtubule. ?The movement towards the pole is slowed down if thekinetochores acquire MicroTubules anchored to kinetochores. The movement of the chromosome becomes directed by changes in length of hte microtubules.?

This is the mechanism by which microtubules attach to the kinetochores and direct the chromosomes to a perticular pole.