The Cell Cycle

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The cell cycle is a sequence of events in the life of a cell, including cell division. Cell division distributes identical sets of chromosomes to daughter cells. This process is used for reproduction, growth, and repair in the body. The cell cycle can be broken down into two parts: interphase and the mitotic (M) phase.

Interphase, a growth period, alternates with mitosis and accounts for 90 percent of the cell cycle. During interphase, the cell grows, duplicates its DNA, and prepares for mitosis. This phase can be broken down into 3 sub phases: G1, S, and G2. During the G1 or first gap phase, the cell grows and performs normal metabolic roles, including producing proteins and organelles. During the S phase, which stands for synthesis of DNA, the cell’s chromosomes are copied. Lastly, in the G2 phase, the cell continues to grow and prepares for cell division. This phase of the cell cycle is regulated by stop and go signals called checkpoints, which are located between G1 and S, G2 and M, and M and G1. These make sure that the cell cycle can proceed and is being performed correctly. The hallmark of this phase is that the DNA appears as loosely packed chromatin and the centrioles are together. Centrioles play an important role in animal cell division. They are composed of microtubules which become spindle fibers that guide the movement of chromosomes in mitosis.

Mitosis is the division of the nucleus, which accounts for only 10 percent of the cell cycle. Mitosis can be broken down into five sub phases: prophase, prometaphase, metaphase, anaphase, and telophase; cytokinesis takes place last. In prophase, the chromatin condenses to chromosomes and the two sister chromatid are joined at the centromere. As the centrioles begin to separate, the mitotic spindle, made of microtubules, begins to form and the nucleolus disappears. In prometaphase, the nuclear membrane dissolves, which allows the spindle to interact with the chromosomes, although the spindle isn’t...
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