Do cells have a life cycle?
Yes, just like a butterfly passes through different phases, such as caterpillar, chrysalis, and adult butterfly, there are a series of phases in a cell's life as it gets ready to divide. The sequence of phases leading up to cell division and then ending with cell division itself is called the cell cycle.
The process of cell division in eukaryotic cells is carefully controlled. The cell cycle (Figure below) is the life cycle of an eukaryotic cell, with cell division at the end of the cycle. Like a human life cycle, which is made up of different phases, like childhood, adolescence, and adulthood, the cell cycle also occurs in a series of phases. The first cell cycle begins with the formation of a zygote from the fusion of a male and female sex cell (gamete).
The steps of the cell cycle can be divided into two main components: interphase and the mitotic phase. Interphase is the stage when the cell mostly performs its “everyday” functions. For example, it is when a kidney cell does what a kidney cell is supposed to do. The cell also gets ready to divide during this time. The cell divides during the mitotic phase, which consists of mitosis and cytokinesis.
Most of the cell cycle consists of interphase, the time between cell divisions. Interphase can be divided into three stages:
- The first growth phase (G1): During the G1 stage, the cell doubles in size and doubles the number of organelles.
- The synthesis phase (S): The DNA is replicated during this phase. In other words, an identical copy of all the cell’s DNA is made. This ensures that each new cell has a set of genetic material identical to that of the parental cell. This process is called DNA replication.
- The second growth phase (G2): Proteins are synthesized that will help the cell divide. At the end of interphase, the cell is ready to enter mitosis.
Shown is the cell cycle. Notice that most of the cell cycle is spent in Interphase (G1, S, and G2). Mitosis and cytokinesis occur during the Mitotic phase. Some cells may enter a resting phase during which progression through the cycle stops.
During mitosis, the nucleus divides as the chromosomes are equally separated. One nucleus becomes two nuclei, each with an identical set of chromosomes. Mitosis is followed by cytokinesis, when the cytoplasm divides, resulting in two cells. After cytokinesis, cell division is complete. The one parent cell (the dividing cell) forms two genetically identical daughter cells (the cells that divide from the parent cell). The term "genetically identical" means that each cell has an identical set of DNA, and this DNA is also identical to that of the parent cell. If the cell cycle is not carefully controlled, it can cause a disease called cancer in which the cells divide out of control. A tumor can result from this kind of growth.
- The cell cycle describes the "life" of a cell.
- Interphase, the stage of the cell cycle when the cell, preparing to divide, is divided into the G1, S, and G2 stages.
- The nucleus divides during mitosis, and the cytoplasm divides during cytokinesis.
Use the resource below to answer the questions that follow.
- Cell Division and Cell Cycle at http://vimeo.com/9536315 (5:34)
- What are the major phases of the cell cycle?
- Why do you think it is important for a cell to grow before it replicates its DNA? Be as specific as you can in your answer.
- What happens during the S phase of the cell cycle?
- What happens during mitosis?
- What is the function of spindle fibers? Where do they attach?
- What is the function of meiosis?
- What is the cell cycle?
- What are the two main components of the cell cycle?
- What occurs during interphase?
- What are the three stages of interphase?
- What is the main purpose of the S phase?
- Describe the main events of the mitotic phase.
- Define cancer.