The Cell Cycle
The Cell Cycle

The cell alternates between interphase and mitosis. It spends the most time
in interphase, and the least time in mitosis, when the cell divides

Cell Division

  • In late interphase, the nucleus is well-defined, with sometimes a few more nucleoli. Just outside the nucleus is a pair of centrosomes (in animal cells centromeres are present there). Microtubules extend from them in star shapes, called asters. There are two sets of chromosomes (they duplicated during S phase), but they are in the loose form of chromatin
  • In prophase, the nucleoli disappear. The chromatin fibers in the nucleus coil more tightly into chromosomes, which consist of two sister chromatids joined in the center by a centromere (which is also the location of the kinetochore). In the cytoplasm, the mitotic spindle, mictrobules extending between the centromeres, forms. The centromeres are now moving to opposite poles of the cell.
  • During prometaphase, the nuclear envelope falls apart. The microtubules extend into the middle of the cell, attaching to the center kinetochore of the chromosome.
  • In metaphase, the chromosomes are moved to the metaphase plate, an imaginary line in the exact center between the centromeres.
  • During anaphase, the paired centromeres of each chromosome suddently separate, and the sister chromatids move toward their respective centromeres as the microtubes attached to them shorten. The poles themselves move farther apart, as the cell lengthens. By the end of anaphase, each of the poles has a complete set of chromosomes
  • In telophase, a nucleus (and nucleolus) begins to take shape in each newly forming daughter cell, from the fragments of the parent nucleus. The chromosomes become less tightly coiled. Mitosis, the division of the nucleus into two daughter nuclei, is complete.
  • Cytokinesis begins with a cleavage furrow forming where the metaphase plate once was. Eventually the cell pinches in two

G2 of Interphase
G2 of Interphase
Mitosis
Mitosis