Cell Theory Reflection

The third principle in the cell theory states that all cells arise from pre-existing cells. Cells are able to do this through the cell cycle. Every cells goes through this process, some more than others. The stages of the cell cycle are the G1, or Gap Phase 1, S phases, or Synthesis Phase, G2, or Gap Phase 2, the Mitosis phase, and the last phase, cytokinesis. There is also a G0 or Gap Phase 0, which occurs in nerve and muscle cells. All of these phases work together for the cell cycle’s end result: two identical daughter cells. Now that I have newly separated from a mother cell, you can follow me through the cell cycle and get an inside look into a normal cell’s everyday life. The first step in the cell cycle and in Interphase is the G1 phase.

During this stage, I will double check everything that occured in the S phase and make sure I did not make any mistakes. If I have made a mistake, I will immediately repair it. Metabolic changes that occur during this phase assemble the cytoplasmic materials necessary for the next two stages in the cell cycle, mitosis and cytokinesis. I will continue growing, producing new proteins, and preparing for division. At the end of G2, a second checkpoint, the G2 Checkpoint, will occur to determine if I can now proceed and enter into the next stage, mitosis. Mitosis contains its own five individual stages: prophase, prometaphase, metaphase, anaphase, and telophase. During prophase, my chromosomes become visible as paired sister chromatids and my nuclear envelope disappears. Sister chromatids are replicated chromosomes that form an X shape thanks to the centromere. They are identical pieces of DNA. Within the cytoplasm, the mitotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the

During this phase, the duplicated genetic material within the nucleus is separated and kinetochores develop around the centromere. Kinetochore microtubules extend from either side of the cell and attach to the kinetochores of my sister chromatids. After these kinetochore microtubules have attached to every chromosome, I will move into the third stage of mitosis, metaphase. During metaphase, my chromosomes align along my equator through a type of cellular “tug of war.” The kinetochore microtubules mentioned in prometaphase pull my sister chromatids back and forth in a “tug of war” fashion until they align on the equatorial plane. A metaphase checkpoint also occurs at this time ensuring that I am prepared for division. After they have aligned and attached, anaphase begins.

During anaphase, the centromeres connecting the two sister chromatids are pulled apart and the separated chromosomes move to opposite poles, pulled by spindle fibers. The separated sister chromatids are then referred to as daughter chromosomes. These spindle fibers make up the mitotic spindle which is connected to my cell’s pole at the opposite end of the attached chromosome. The sister chromatids are pulled apart at the same time by the centromere, ensuring that I have identical