Final answer:
In cell division, the M checkpoint ensures sister chromatids are correctly attached to the spindle microtubules, leading to M-Cdk inactivation and exit from M-phase for successful mitosis and cytokinesis.
Step-by-step explanation:
In the spindle assembly checkpoint of cell division, the M checkpoint occurs near the end of the metaphase stage of mitosis and is also known as the spindle checkpoint. It plays a crucial role in ensuring that the sister chromatids are correctly attached to the spindle microtubules. Tension in the spindle apparatus tugs at the kinetochores, and when this tension is sufficient, it leads to the inactivation of M-Cdk and the eventual exit from M-phase. The activated separase enzyme then allows for the chromatids to separate at their centromeres. The successful passing of the M checkpoint indicates that the cell will complete mitosis and cytokinesis, leading each daughter cell into a new G1 phase.