Events in the different phases and stages of the cell cycle

  Created March 2020, Offline version here
  Video by Dillon Brantley, also on his YouTube channel.




    The cell cycle is the process through which the cell divides. The cell cycle can be split into two phases: interphase and . Cells spend most of their life in interphase, carrying out normal processes. It only leaves interphase to divide. The cell cycle is a tightly regulated process; if the cell divides uncontrollably, it can lead to . Interphase can be divided into three stages G1, , and G2. During the G1 phase, the cell is in a key period of and may also increase the numbers of its organelles. During the S phase, the cell the DNA.
    is the final stage before mitosis and involves further growth and preparations for mitosis. The control of the cell cycle is primarily achieved by . The G1 checkpoint ensures that all the procedures in G1 happened adequately and that internal and external conditions are good for cell division. The G2 checkpoint is the final checkpoint before mitosis proceeds and checks that chromosomes have been properly replicated, and that the DNA isn’t . The M checkpoint happens after mitosis has begun, but before it is complete, and ensures that the are correctly attached to the spindles. The molecules that are responsible for regulating the cell cycle are called . Different cyclins are present at different throughout the cell cycle, reflecting their involvement in regulating different stages and checkpoints. One of the primary ways that cancer develops is when the checkpoints , so is not making the necessary checks before dividing. After the G2 checkpoint, can proceed. Mitosis is the actual process of cell division, where two cells are made from the parental cell. This involves passing a complete copy of the recently duplicated genome on to each new cell. Mitosis has four stages in which it can be divided. They occur in the following order: . Mitosis begins with a duplicated genome. This means each X-shaped chromosome is made up of two sister ,held together in the middle by a structure called a . During prophase, the chromosomes start to become visible when looking down the microscope because they have up into tightly compact structures. Additionally, spindles, which are structures made of ,start to form from the . The nucleolus disappears, and the nuclear starts to break apart to allow the chromosomes to become released from the nucleus. The second phase is metaphase. Once the nuclear membrane has broken down, the chromosomes start in the center of the cell. This happens because of the actions of the spindles. The spindles attach to chromosomes at the centromere and move them to the middle of the cell. After metaphase, the anaphase stage begins. In anaphase, the sister chromatids that make up the chromosome are and moved to opposite sides of the cell. They are now referred to as . The final stage of mitosis is . In this stage, the chromosomes are at opposite sides of the cell. The forming daughter cells are still connected. The microtubules that form the spindle break down, the nuclear membrane reforms, and the chromosomes start to uncoil. After telophase, proceeds, which separates the cytoplasm of the two cells.