Final answer:
The cell is in the prophase stage of mitosis, where sister chromatids are attached at their centromeres and the nuclear envelope is partially broken down.
Step-by-step explanation:
In the given scenario, the cell is in the prophase stage of mitosis. During prophase, the sister chromatids are attached at their centromeres and the nuclear envelope starts to break down, allowing access to the chromosomes. Additionally, the microtubules that form the mitotic spindle begin to extend between the centrosomes, pushing them apart.