MoBio Mitosis Chapter 8

Mitosis is a process of cell division resulting in two genetically identical daughter cells. The stage between mitoses is called the interphase which covers the G1, S, and G2 phases of the cell cycle. During the G2 phase, DNA has been replicated and the chromosome number is 4n. In the interphase, chromosomes are not visible by light microscopy because the chromatin diffuses throughout the nucleus.

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Figure 8-B-1. Phases of mitosis.

Mitosis may be divided into the following phases.

  • Prophase: The chromatin condenses into chromosomes. Two centrioles move toward the opposite ends (poles) of the cell. Microtubules radiate from each centriole, forming a structure called "spindle". By the end of prophase, the nuclear envelope breaks down into small vesicles.
  • Metaphase: The chromosomes align at the equatorial plane of the cell, as directed by the microtubules attached to the kinetochore (located at the centromere of each chromosome).
  • Anaphase: Sister chromatids separate and move apart. The separation happens simultaneously for the entire set of chromosomes. The microtubules attached to the kinetochore also play a critical role in this process.
  • Telophase: The chromosomes begin to uncoil and become less condensed. The spindle disappears while the nuclear envelope reappears. The cell elongates and eventually divides into two daughter cells. The process of cell division is called "cytokinesis."

The morphological changes in early mitosis are mainly due to the phosphorylation of related proteins catalyzed by MPF. The mitosis is terminated by the activation of DBRP.