By Iman Kagimu
Edited by Eman Hamed
The study of mitosis occurs in a biology or life science class, usually in middle school and then in high school. In simpler terms, mitosis is the process of dividing cells to produce more genetically identical cells. There is another type of cell division, meiosis which creates egg and sperm cells, we’ll study that another time. Mitosis is the fundamental process for life to occur.
In mitosis the mother cell divides to create two new daughter cells, the DNA of the cell’s nucleus has to be split into two equal sets of chromosomes. There are 6 steps in mitosis; interphase, prophase, metaphase, anaphase, telophase, and cytokinesis. Interphase occurs before mitosis, in this phase the DNA is already copied and the chromosomes in the nucleus have 2 connected copies, these are the sister chromatids. Outside of the nucleus is the centrosome and it’s copy, which each have a pair of centrioles, they will have an important role later. Here are some essential terms and definitions. The nucleus houses DNA and the nucleolus which helps produce ribosomes. Centrioles have microtubules that help separate chromosomes during cell division. The centrosome directs the movements of the microtubules. Chromosomes are thread-like structures, it is made up of DNA and is not visible at all, but the DNA can be visible under a microscope. A chromatid is an identical half of a replicated chromosome.
In the start of prophase, the cells break down and build structures. The chromosomes condense and the mitotic spindle starts to form, which will organize and move the chromosomes, it grows between the centrosomes as they move apart. The chromosomes look like X-shaped structures. The nucleolus where ribosomes are made will then go away, which is a signal that the nucleus is ready to break down and split. In the end of prophase, also known as prometaphase the mitotic spindle starts to organize the chromosomes as they become more compact and the nuclear envelope breaks and releases the chromosomes. The spindle has microtubules which extend across the cell between the centrioles.
In metaphase, the spindle has all of the chromosomes and lines them up in the middle. The cell checks that the chromosomes are attached to the microtubules. If a chromosome isn’t properly attached the cell will pause the phase for any issues to be fixed. However, if the cells do not align correctly in this phase then they can’t move to opposite sides in the later phases, which results in one cell having extra chromosomes and one cell with missing chromosomes. This leads to mutations, diseases, or cancer.
In anaphase, the sister chromatids will be separated and pulled towards opposite ends of the cell due to the protein “glue” being broken. The chromosomes for each sister chromatid are pulled towards their directed side of the cell and the microtubules push apart and make the cell larger in size.
In telophase, the cell has almost finished the cell division process. The spindle is broken down and disappears. The nuclear membranes nucleoli reappear for each set of chromosomes and the chromosomes decondense and return to their original form from Step 1.
Lastly, cytokinesis can occur in anaphase or telophase, it depends on the cell, and ends after telophase. It is the division of the cytoplasm to create the two new cells. The single cell pinches down the middle to create two separate new daughter cells, the separation between the two is called the cleavage furrow. The process of cell division is now over!