 In this video, I will list the phases of the cell cycle, describe the events that occur in each phase of interphase, which are G1, SNG2, and then explain why DNA replicates and when during the cell cycle DNA replication happens. Here we have an illustration showing the phases of the cell cycle, and the cell cycle is a sequence of events through which the cell is preparing to divide, making two daughter cells from one initial mother cell. It's important for us to think a little bit about why does the cell go through this cell cycle, why does the cell bother dividing? Well, cell division is necessary for reproduction. Cell division called meiotic cell division, which involves two rounds of cell division, will produce unique daughter cells that have a unique set of genetic instructions. And these are the sperm cell and ovum that will then unite in the process of fertilization to produce a zygote that will develop into an embryo and then fetus. Cell division is also necessary for growth as the embryo grows into a fetus and as an infant grows into a child and eventually an adult, that growth, the expansion of our body, expansion of tissues in our body will require division of cells so that the tissue can become larger. Cell division is also necessary to maintain some of our tissues. For example, the epidermis of our skin, the top layer of our skin, is constantly losing cells from the surface that break off and dry out and die. And new cells are constantly being produced deep in the epidermis in order to repair those cells in order to repair that tissue and to replace those cells that have been lost in order to maintain that tissue. Similarly, regeneration, if you were to have a cut in your skin, cell division would enable those tissues to repair in the process of regeneration. The cell cycle goes through a sequence of phases starting with the G1 phase where cells typically spend the majority of their life growing and carrying out everyday functions. During the G1 phase, the cell can accumulate the nutrients that would be required to enter into the DNA synthesis process that occurs in S phase. S phase is the second phase of the cell cycle and S stands for synthesis. During S phase, DNA is replicated and so the new copy of DNA is synthesized. This is important because we need to have an extra copy of the genetic instructions to pass on to a second cell in cell division. The third phase of the cell cycle is known as the second growth phase or the G2 phase. The G2 phase is a phase when the cell is accumulating nutrients and checking to make sure that the DNA replication went without any major errors after the DNA has been replicated and there's no major problems with DNA replication. The cell needs to make sure it has enough nutrients to prepare for dividing and producing two new daughter cells. And so the G2 phase provides a final checkpoint to make sure everything's ready for mitosis. Together G1, S and G2 are known as interphase of the cell cycle. In contrast to interphase, the mitotic phase of the cell cycle or M phase of the cell cycle is when the cell will divide and produce two nuclei. The process of mitosis is the division of the nucleus producing two nuclei inside of one cytoplasm. Then following mitosis, cytokinesis is the division of the cytoplasm which will produce two new daughter cells. One nucleus in each of the new cells will contain a complete copy of the genetic instructions.