The cell cycle controls the four major phases of cell growth and division. These phases are the growth phase 1, the synthesis phase, the growth phase 2 and mitosis. The cell’s DNA is copied during the synthesis phase. During each step of the cell cycle, there are checkpoints to ensure that the cell is ready to progress to the next phase, regulated by a protein called cyclin. If the cell has not properly copied its chromosomes, an enzyme called cyclin dependent kinase, or CDK, will not activate the cyclin, and the cell cycle will not proceed to the next phase. The cell will undergo cell death. When there are problems or mutations with the cyclin, cell growth proceeds unchecked, and can lead to cancer.
The growth of all cells is governed by the cell cycle, including cell division. Before a cell can divide, many processes must occur, including the proper duplication of the chromosomes. The cell cycle ensures that all of these processes occur normally, otherwise the cell ceases to progress and could die.
The Cell Cycle
The life of a cell is controlled by the cell cycle, including its division. The cell cycle has four major phases: growth phase 1, synthesis phase, growth phase 2 and mitosis. During growth phase 1, or G1, the cell grows in size in response to certain proteins known as growth factors. A copy of the cell’s DNA is made during the synthesis, or S phase. Growth also occurs during the second growth phase, or G2. Mitosis is the phase when the cell actually divides into two cells, known as daughter cells.
DNA Replication
DNA is copied or replicated during S phase. During this time, the chromosomes are copied, so that there is a complete set of chromosomes for each daughter cell. First, an enzyme called DNA helicase unwinds the two strands of the DNA double helix. Then another enzyme, DNA polymerase, binds to the DNA strands and causes complementary nucleotides to bind to each of the strands. Finally, another enzyme, DNA ligase, binds the newly formed, complementary strands to the existing strands.
