Question

1A. (6pts) What does it mean for a chromosome to be correctly attached to a spindle, and how

does a tension sensor in the cell cycle distinguish correct vs. incorrect attachment?

B. (4pts) How does the tension sensor in the cell cycle prevent aneuploidy?

C. (6pts) Would this tension sensor be effective in preventing aneuploidy in the event of a double-stranded DNA break? Please provide your reasoning.

Answer 1

Ans a) The accuracy of the chromosome to be correctly attached to the microtubule spindle is to be held by the kinetochores. When the chromosome is not held properly to the spindle, the kinetochores is responsible for activating the spindle assembly checkpoint network. This leads to blocking the cell cycle progression. The binding of the kinetochores to the spindle fibres is the right and accurate binding of the chromosome. There are many checkpoints in the cell cycle which helps in finding out if the binding of the chromosome to the spindle is accurate or not. The mitotic spindle checkpoint takes place in the metaphase and is the phase where a chromosome is aligned at the mitotic plate. There is a tension that is created due to the bipolar attachments which is being sensed and helps in understanding the alignment. The sensing mechanism make sure that the anaphase promoting complex is not inhibited and is free to degrade the cyclin B and break down securin.

Ans b) During the cell division, there are spindle checkpoint that prevents separation of the chromosomes that has been duplicated until each is properly attached to the spindle apparatus. Aneuploidy is a situation where daughter cell is formed with abnormal number of chromosome, it may be less or more chromosome. During the metaphase, the kinetochores are attached to the mitotic spindle and the Aurora-B/Lpl1 kinase of the chromosomal passenger complex is responsible as tension sensor which helps in detecting improper kinetochore attaches. It helps in destabilizing the incorrect attachments by control of the microtubule severing KINI kinesin MCAK along with the DASH complex and Ndc80/Hec1 complex at the interface of the microtubule-kinetochore.