What structure breaks down during prophase of cell division?

During prophase of cell division, the nuclear envelope breaks down as part of the preparatory steps for mitosis. This breakdown is a critical event that facilitates the separation of chromosomes into daughter cells. The nuclear envelope, which is a membrane that encloses the nucleus, dissolves to allow microtubules to access the chromosomes that need to be segregated.

This process is essential because, without the degradation of the nuclear envelope, the spindle apparatus cannot properly attach to the chromosomes. As the phases of mitosis proceed, this degradation ensures that chromatin condenses into distinct chromosomes and that the spindle fibers can interact with the kinetochores of those chromosomes, ultimately leading to their proper separation during metaphase and anaphase. In summary, the breakdown of the nuclear envelope is a key transition that facilitates the organization and movement of genetic material during cell division.