prometaphase

Prometaphase is the second phase of mitosis, the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. During prometaphase, the physical barrier that encloses the nucleus, called the nuclear envelope, breaks down. The breakdown of the nuclear envelope frees the sister chromatids from the nucleus, which is necessary for separating the nuclear material into two cells. Another important event during prometaphase is the development of a protein formation called a kinetochore around the centromere, the central point joining the sister chromatids. Long protein filaments called kinetochore microtubules extend from poles on either end of the cell and attach to the kinetochores. Prometaphase is followed by the third phase of mitosis, known as metaphase.