Spindle Checkpoint - Metaphase To Anaphase Transition

Metaphase To Anaphase Transition

The beginning of metaphase is characterized by the connection of the microtubules to the kinetochores of the chromosomes, as well as the alignment of the chromosomes in the middle of the cell. Each chromatid has its own kinetochore, and all of the microtubules that are bound to kinetochores of sister chromatids radiate from opposite poles of the cell. These microtubules exert a pulling force on the chromosomes towards the opposite ends of the cells, while the cohesion between the sister chromatids oppose this force.

At the metaphase to anaphase transition, this cohesion between sister chromatids is dissolved, and the separated chromatids are pulled to opposite sides of the cell by the spindle microtubules. The chromatids are further separated by the physical movement of the spindle poles themselves. Premature dissociation of the chromatids can lead to chromosome missegregation and aneuploidy in the daughter cells. Thus, the job of the metaphase checkpoint is to prevent this transition into anaphase until the chromosomes are properly attached, before the sister chromatids separate.