The cell is the unit of life. One of the main characteristics of these is probably the ability of these living things to reproduce.
All cells reproduce by dividing into several daughter cells, which in turn can continue to proliferate. In the case that belongs to us as a human being, that is to say in eukaryotic cells, there are two types of division: mitosis and meiosis. For this occasion, I will focus on the first of them and explain the phases of mitosis it performs to effect the formation of two daughter cells.
The common phase
The cells follow the pattern of a sequential process that ends with cell division. This process is known as the cell cycle. In a nutshell, the cycle is to prepare the cell for its impending partition of two. This process has traditionally been divided into two main phases: the interface and the M phase. The latter would be the mitosis phase itself. The interface is shared in both mitosis and meiosis.
If the eukaryotic cell cycle took 24 hours, the interface would occupy 23 hours, leaving only one hour for its division. It is normal for it to take so long, because at this point the cell doubles in size, doubles its genetic content and prepares the necessary tools for all to go well in the formation of new cells.
The interface, in general, is divided into three stages:
- Phase G1 (GAP1): the cell it grows bigger and is metabolically active.
- Phase S (synthesis): the cell replicates its DNA.
- Phase G2: the cell continues to grow and synthesizes proteins that will be used for mitosis.
Once the cell enters the S phase, there is no going back to the process of division, unless it is detected that its DNA is damaged. Cells have signaling systems that allow their DNA to be recognized and if something goes wrong they can stop the process so as not to cause more problems. If all goes well, the cell is ready for its imminent proliferation.
Stages of mitosis
After completing the interface, the cell enters the M phase in order to form new cells. Mitosis results in two sister cells of equal genetic content. Mitosis has some differences depending on the eukaryotic cell that makes it, but they all have in common the condensation of chromosomes, the formation of the mitotic spindle, and the union of chromosomes to it … many new concepts that I will clarify .
Traditionally, mitosis has been divided into four labeled stages: prophase, metaphase, anaphase, and telophase. To explain this process, I will focus on the case of human cells.
At the start of M phase, DNA replicated that it is matted and condenses into a more compact form known as a chromosome. In the case of humans, we have 23 chromosomes. As it is always preparing to separate, the chromosomes are always formed by the two chromatids (the original and the copy), joined by a midpoint called a centromere, giving the typical image of an X.
Not only does this happen; it must be remembered that genetic material is inside a nucleus, And to access them, the membrane that surrounds them must be degraded. In addition, the mitotic spindle is generated, a collection of filamentous protein structures (microtubules), which will later act as chromosomal transport pathways.
when these mentioned microtubules bind to the centromere of chromosomes and they line up just in the center of the cell when metaphase occurs. It’s already at the point where the genetic content is separating. It is a phase of rapid mitosis.
In this phase of mitosis, you will understand how the mitotic spindle works. What it does is separate the sister chromatids and slide them to opposite poles, as if it were a fishing rod picking up the line. This makes it possible to obtain the same genetic content in the two new cells.
Once on opposite sides, the chromosomes are decondensed in their usual form and the nucleus containing them is regenerated. Next to this occurs cytokinesis, that is, the partition into two cells. This process begins at the end of anaphase, and consists of the case of animal cells in a contractile ring which strangles the cell membrane more or less through the center, as if it were a balloon, until what it reaches two independent cells.
The end result of mitosis is the formation of two interphase sister cells, as they contain the same genetic content and there has been no modification of it, it was simply replicated. It should be noted that any anomaly in this process stops it immediately.