The two main phases of cell division are interphase and the mitotic phase. Interphase accounts for about 90% of the process while the mitotic phase accounts for the other 10%. Interphase can be further divided in three sub-phases:G1 phase, S-Phase, and G2 phase. All three phases consist of the cell growing by producing protein and cytoplasmic organelles. After some growth of the cell occurs in G1 phase, the cell grows even more during the S-Phase as the cell copies its chromosomes. The cell completes growing during the G2 phase and then divides after the mitotic phase.
Mitosis, the division of the nucleus, is broken into five sub-phases: prophase, prometaphase, metaphase, anaphase, and telophase. During prophase chromatin fibers become tightly coiled and the chromosomes condense. The nucleoli disappear and the centrosomes move away from each other. In the cytoplasm, the mitotic spindle, made of microtubules, begins to form. During prometaphase the nuclear envelope disappears and fibers of the mitotic spindle interact with the condensed chromosomes. Each of the two chromatids of a chromosome now has a kinetichore, a structure of proteins and specific sections of chromosomal DNA at the centromere. A chromatid is the DNA protein complex organized into long, thin fibers. During metaphase the centrosomes are at opposite poles of the cell, and the chromosomes come together at the metaphase plate, the equator of a cell. During anaphase the paired centromeres split and move to opposite poles of the cell. The microtubules pull the centromeres by shortening, and since the centromeres are attached to the microtubules they go along. During telophase the nuclear envelope reforms around the chromosomes and the chromatin fiber of the chromosomes becomes less dense. Each half of the cell now has everything needed to become its own cell except for the cytoplasm, which is being produced.
