Mitosis

 Mitosis

    Many people learn about mitosis when they are in middle school, the first time I remember learning about mitosis was in 7th grade, and then I learned about it again in high school biology. So, it's not something that you probably have no idea what it is, but there is much more to it than you probably think! So, first I am going to go over the basics. What is mitosis? Mitosis has to do with the things we see in everyday life! The plants we see, the intestines in our body, the birds you see, and so much more all are made of cells, and go through mitosis. Mitosis is the process where a cell replicates its chromosomes and then segregates them, making two identical nuclei in preparation for cell division. Mitosis is generally by equal cell division of the cells content into two daughter cells that have identical genomes. To break it down even more you could say this, it is like making copies of an instruction manual. Copy each page, and then give one copy to every two people. In mitosis, a cell copies each chromosome, and then gives a copy to each two daughter cells. When making the copies of the instruction manual, make sure that it is copied word for word and that there is no grammar problems. If you do that then it would be hard for the people to follow the instructions if they can't read it. This is the same for mitosis, each cell needs to receive exactly one copy of each chromosome, and each copy needs to be perfect, no mistakes or the cell will have trouble following the genetic instructions. The cells have amazing systems to copy chromosomes almost perfectly and to make sure one copy goes to each daughter cell. There still are some mistakes that can take place when copying or dividing cells, it is very rare but still possible. This can result in some hard consequences for the person and the cells. 

Prophase

    Now that we got the basics of this out of the way, we can get more in depth with the phases and how they work! There are five different phases that go into mitosis, I know you're probably thinking that sounds like a lot, but I promise once you get them down, they all come together and make sense. The first phase of mitosis is prophase. During this phase, chromosomes recruit condensing and undergo a condensation phase. I know that may sound confusing, so I'll explain it more. It is the first and longest phase in mitosis. During this, chromatin condenses into chromosomes, and the nuclear envelope (the membrane around the nucleus) breaks down. In animal cells, the centrioles near the nucleus begin to separate and move to opposite poles of the cell. Centrioles are small organelles found only in eukaryotic cells that help ensure the new cells that form after cell division each contain a complete set of chromosomes. As the centrioles move apart a spindle starts to form between them.

Metaphase

    After that happens, a new phase begins to start. This is called Metaphase. After the spindle fibers fully attach to the centromere of each sister chromatids, they begin the align in the center of the cell(like in the picture below). During this, the nucleus is dissolving. These spindle fibers ensure that the sister chromatids will go to different daughter cells when the cell divides.

Anaphase

    During anaphase, sister chromatids separate, and the centromeres divide. The sister chromatids are pulled apart because of the shortening of the spindle fibers. This is like reeling in a fish by shortening the fish line. Through this each sister chromatid goes to opposite sides of the poles.

Telophase

    The chromosomes are on the opposite side of the poles, and they then begin to break down. This is when telophase begins to start! During this phase a nuclear membrane (the nuclear envelope) on each chromosome begins to form, some people may say the cytoskeleton which makes more sense because it is the "skeleton" of the cells. This separates the nuclear DNA from the cytoplasm. So, the daughter cells are beginning to separate but they aren't split yet. 

Cytokinesis

    This is finally the last step to mitosis! So, we are almost done! During this step the two daughter cells fully separate from each other. It is different for animal and plant cells. In animals it looks like two small circles squished together and the line in the middle of them separating them is called, the cleavage furrow. In plant cells, they have a cell wall and in the middle of this cell is a structure called the cell plate. So the two daughter cells are separated by a wall. When this is finished, there are now two new cells, each with a complete set of chromosomes.

    

Sources:

Donald B. Mcmillan, Richard J. Harris (2018), An Atlas of Comparative Vertebrate Histology

Cell Biology (3rd edition), 2017 

Daniel A. Gilchrist 2024, National Human Genome Research Institute