Final answer:
Exit from mitosis is triggered by the degradation of cyclin B. DNA organization in a eukaryotic cell is initially maintained by condensin, and the spindle fibers attach to chromosomes via the kinetochores during prophase.
Step-by-step explanation:
Exit from mitosis depends upon the degradation of cyclin B. This protein is part of a regulatory system that controls the progression of the cell cycle. Specifically, cyclin B forms a complex with cyclin-dependent kinase (Cdk), which functions to phosphorylate other proteins, leading to their activation or inactivation. The concentration of cyclin B fluctuates throughout the cell cycle, with its degradation marking the cell's exit from mitosis.
The first level of DNA organization in a eukaryotic cell is maintained by condensin proteins, which help sister chromatids coil during prophase. As the cell progresses into anaphase of mitosis, cohesin proteins degrade, allowing sister chromatids to separate. These processes are crucial for the correct distribution of chromosomes into daughter cells. Additionally, the fibers made of microtubules that attach to the centromeres during mitosis are called spindle fibers, and the characteristic attachment of these fibers to the kinetochores occurs during prophase.
The nuclear envelope breaks down at the start of mitosis to allow the spindle fibers to attach to chromosomes, enabling their proper segregation during cell division. During anaphase, the chromosomes, with the aid of spindle fibers, begin their migration to the opposite poles of the cell, which eventually leads to the ultimate step of mitosis, cytokinesis, where the cytoplasm divides forming two daughter cells.