Cell growth can refer to the expansion of a single cell as it prepares to divide or to the expansion of a population of cells that is growing through cell division. Both of these processes are parts of the cell cycle. A number of events occur as a cell prepares to divide, and eventually split, into two identical daughter cells.
The process of cell growth, both within the cell itself and within the cell population, begins with a resting phase, known as gap 0. During this phase, the cell metabolizes as normal but is not actively growing. After this period of rest, which differs depending on the type of cell, the cell enters the interphase part of the cell cycle.
The first step of interphase is another period of rest, called gap 1. During this time, the cell grows to prepare for the presence of additional deoxyribonucleic acid (DNA). It also develops the additional cytoplasm it will need in order to divide into two full-sized cells at the end of the process. During the next step in interphase, the DNA is unzipped and replicated to create two sets of chromosomes. In gap 2 of interphase, the cell checks to make sure that the DNA has replicated properly and continues growing until it is large enough to divide.
After interphase, the next step in cell growth is mitosis, which is broken into four separate steps. During mitosis, the cell itself stops growing and creating additional protein and begins the process of dividing the replicated chromosomes onto opposite sides of the nucleus. In the first step, called prophase, the chromosomes condense and spindle fibers move to opposite poles in the cell.
The second step is metaphase, in which the chromosomes align themselves along the central axis of the cell. The spindle fibers attach to the duplicate sets of chromosomes, while in anaphase, each set of chromosomes begins to be pulled away from the center. The chromosomes complete their move to the opposite sides of the cell during telophase, which is the last stage of mitosis. The chromosomes then uncoil, and a nuclear membrane appears around each set of chromosomes.
The final stage in cell growth involves the actual splitting of one cell into two daughter cells. In this process, known as cytokinesis, the cytoplasm itself divides. This increases the population of cells in the area and sends the two daughter cells back to a resting phase until the body informs the cells that they need to grow and divide again.