The Cell Cycle

The cell cycle consists of seven different processes in which a cell divides to create a new, exact copy of the original cell. Interphase is the first process. During interphase the cell grows to synthesize new molecules and organelles. It doubles the original content and contains two centrosomes. The chromosomes in the nucleus are duplicated. Next is prophase. Changes occur in the nucleus and the cytoplasm. The chromatin fibers are more tightly coiled, which forms discrete chromosomes. Each chromosome appears as two identical sister chromatids. In the cytoplasm, a mitotic spindle forms as microtubules grow rapidly from the cenrtosomes. They begin to slowly move away from each other pulling the chromosomes in half. During prometaphase the nuclear envelope breaks in into fragments. At metaphase the mitotic spindle is completely formed. Anaphase starts as the centromeres of each chromosome pull apart. They then move towards opposite poles of the cell. The poles then move further and further apart causing the cell to elongate. At the end of anaphase, both sides of the cell have an equal number of chromosomes. In telophase the elongation that started in anaphase continues, daughter nuclei appear at the poles and envelope the chromosomes. Telophase is the reverse of prophase. The final stage, cytokinesis, usually occurs at the same time as telophase. This is when the division of the cytoplasm happens. In animals a cleavage furrow forms and the cell splits into two new cells.

Source - Biology: Concepts and Connections by Neil A. Campbell - pages 130 - 131.

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