Question

2) You are trying to examine how tension of the microtubule network impacts the triggering of cell division. You have the ability to: sever microtubules in a directed fashion using a laser and the ability to pull on a kinetochore using a filament. What would you expect to see occuring to the rate of cell division in cells exposed to each of these treatments during prometaphase and describe what is happening in terms of proteins at the kinetochore.

2) You are trying to examine how tension of the microtubule network impacts the triggering of cel division. You have the ability to: Sever microtubules in a directed fashion using a laser and the ability to pull on a kinetochore using a filament. What would you expect to see occuring to the rate of cell division in cells exposed to each of these treatments during prometaphase and describe what is happening in terms of proteins at the kinetochore.

Answer 1

Microtubules is one of the cytoskeleton protein fibres that are comprised of long polymers of tubulin. Each unit of microtubules is comprised of a heterodimer of $\alpha$ tubulin and _$\beta$ tubulin. They are hollow tubular structures with approximately 25nm diameter. They have functions in cell shape maintenance, cellular division, cell motility and intracellular transport.

During cell division, microtubular dynamics converges mechanical as well as chemical force to direct chromosomal movement. Kinetochore is an molecular interface that attaches microtubules to the chromosomes. It is capable of capturing microtubular proteins and nucleate them. Microtubules are structurally stiff and rigid. As the sister chromatids gets attached to microtubules at two opposite sides via kinetochores and orient themselves, they begin to experience tension. This tension further stabilizes the attachment. Once the kinetochore senses the right amount of tension, it signals the cell that the sister chromatids are ready to separate and paves the path for anaphase. The chromatids are then pulled apart by microtubular dynamics.

Our experiment involves two molecular tweaking mechanisms to simulate dividing cells:

1. we can sever microtubules in a directed fashion using a laser
2. we can pull on a kinetochore using a filament

If we employ the above mentioned techniques, we can expect to see:

1. when we sever microtubules involved in attachment to a chromatid via kinetochore, the disruption will ease the tension at the kinetochore-chromatid region. Kinetochore will sense the abnormal destabilizing tension and through a signaling cascade inform the other cellular apparatus that the sister chromatids are not ready to separate and the cell division progression would halt until and unless a stable microtubular association is established again.
2. when we pull on a kinetochore using a microtubule filament, with the right amount of force, the right amount of tension can be established at the kinetochore. This will be sensed as a stable attachment to the microtubles and the kinetochore will signal the cells to proceed with the cell division. The cells will prepare itselt to exit metaphase to enter anaphase, thus increasing the rate of cell division.