Overview of Cell Biology/Mitosis
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Mitosis is the process by which nucleated cells duplicate. See more at [[[w:Mitosis]]]
Mitosis is one of the phases of the cell cycle, which is described in below:
The cell cycle is a concept that describes the life of a cell, from its “birth” to its “death”. Although this introduction will be of a basic nature, cell cycling problems are of extreme interest to scientists. Cells that will not progress normally through their life cycle are at the heart of many human diseases, such as neurogenerative disease, tuberous sclerosis, arthritis, glomerular disease, cardiovascular diseases, and cancer, just to name a few. For example, a cancerous cell is simply a cell has speeded up the reproductive process and it will not die easily.
The “brain” of a cell is its DNA. DNA stands for DeoxyriboNucleic Acid, a chemical name that describes the nature of DNA molecules. DNA has four different nucleic acids, which are referred to by their first letters: A (Adenosine), T (tyrosine), G (guanine), and C (cytosine). The chains of nucleic acids are stored in the nucleus as coiled helices called chromosones. Humans have 46 chromosones which appear X-shaped under the microscope, with the exception that the 46th chromosone may instead be the Y-shaped chromosone which establishes the gender of its carrier as male. The four acids in different combinations provide the code so that the cell may synthesize all the materials (proteins) which make up the body. During interphase, (G1) the gap phase of the cell cycle when the cell is just growing larger, the DNA is kept loose so that enzymes can access and “read” its code to make proteins.
Eventually, the cell will need to copy its DNA in order to pass it on to two daughter cells. This phase of the cell cycle is known as S phase, for the “synthesis” of the copy of the DNA.
After S phase, there is another interphase, known as Gap 2, or G2. Then mitosis starts off the M phase. In M phase, the two copies of DNA are seperated from each other and one copy each is given to each “daughter”. The daughters are actually the cell itself divided into two halves, each half having what a whole cell needs. During mitosis, the DNA becomes visible within the nucleus of the cell (its home) because the chromosones are duplicates folded up tightly. Then they are lined up across the middle of the nucleus and then the copies are pulled apart to opposite poles of the cell.
After this has occurred, cytokinesis can then ensue. In this process, the cell itself divides, and each “pole” becomes a new nucleus in the new cells.
Cells of the skin, gut, immune system, and hair go through the cycle much more often than other tissues of the body. If a cell is not supposed to continue reproducing, it exits the cell cycle and enters a state called G0. The cell cycle is regulated by checkpoints at end of each phase. Before it can continue to the next phase, the cell first has to have miminal levels of DNA damage. DNA is damaged by free radicals such as those from sunlight and junk food. The cycling of the cell is controlled by proteins known as cell cycle regulators such as cell cycle inhibitors, one of which is p53, and cyclins (and their dependent kinases).