The cell cycle and apoptosis are connected to one another through the fact that apoptosis is the natural end of a cell’s life and that cell’s cell cycle. Cells that continue to cycle indefinitely can quickly cause health problems, including cancer, in a large organism. Controlling the life of the cell is important in order to maintain a steady number of cells and to replace old cells with newer ones. After apoptosis begins, a cell ceases to cycle and begins to break down into its component pieces.
Apoptosis is the mechanism by which large populations of cells are culled. During the normal cell cycle, cells divide and rest at a predictable rate, depending on a variety of environmental factors, including the presence of sufficient nutrients and space. If too many cells are allowed to multiply, the process of apoptosis may be started for some of them so that the number of cells does not exceed the number that the environment can support.
In healthy cells, both the cell cycle and apoptosis are carefully regulated through a variety of chemical signals. Cells may cycle into apoptosis when resources or space are limited or when they have grown too old. Old cells are replaced by young cells through the predictable cycle of cell growth, division, and apoptosis so that the proper number of cells continues to exist in an organism. Unregulated, cell counts can rise or fall dramatically.
In cancerous cells, the cell cycle and apoptosis are not regulated properly. Cancerous cells multiply quickly, often skipping the resting stage of the natural cell cycle. They also do not respond to triggers that cause normal cells to go into apoptosis, making it possible for tumors to grow rapidly and aggressively.
The cell cycle and apoptosis are also linked by the predictable, orderly fashion in which these two processes occur. When a cell is getting ready to divide, chemical signals instruct the chromosomes to replicate and line up on opposite sides of a midline. As it divides, the cell membrane changes shape and pinches around each set of organelles and genetic material to form two new cells. In apoptosis, organelles stop replication and line up along the cell membrane. The membrane then pinches around each organelle individually, creating small packets of cellular material that can be consumed and metabolized by other cells.