The 4 phases of mitosis: how the cell duplicates

This is the process by which a cell divides into two cells that are identical and have the same DNA.

The cell is the unit of life. Probably, one of the fundamental characteristics of these is the capacity of these living beings to reproduce themselves.

All cells reproduce by dividing into several daughter cells, which in turn can continue to proliferate. In the case of human beings, i.e. eukaryotic cells, there are two types of division: mitosis and meiosis. For this occasion, I will focus on the first of them and will explain the phases of mitosis that it performs to carry out the formation of two daughter cells.

The common phase

The cells follow the pattern of a sequential process that concludes in cell division.. This process is known as the cell cycle. In short, the cycle consists of preparing the cell for its imminent splitting in two. This process has traditionally been divided into two major phases: the interphase and the M-phase. Interphase is shared in both mitosis and meiosis.

If the eukaryotic cell cycle took 24 hours, interphase would occupy 23 of these, leaving only one hour for division. It is normal that it takes so long, since during this stage the cell doubles its size, doubles its genetic content and prepares the necessary tools so that everything goes well in the formation of new cells.

Interphase is generally divided into three stages:

• G1 phase (Gap1): the cell grows in size and is metabolically active..
• Phase S (Synthesis): the cell replicates its DNA.
• G2 phase: the cell continues to grow and is metabolically active. synthesizes proteins that will be used for mitosis..

Once the cell enters the S phase, there is no turning back in the division process, 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, the process can be stopped so as not to cause further problems. If all is well, the cell is ready for imminent proliferation.

Phases of mitosis

After the end of interphase, the cell enters the M-phase with the aim of forming new cells.. Mitosis results in two sister cells, of equal genetic content. Mitosis has differences depending on the eukaryotic cell that performs it, but they all have in common the condensation of chromosomes, the formation of the mitotic spindle and the union of chromosomes to these last .... many new concepts that I will clarify.

Traditionally, mitosis has been divided into four distinct stages: prophase, metaphase, anaphase and telophase. To explain this process I will focus on the case of human cells.

1. Prophase

At the beginning of the M-phase, the replicated DNA that is entangled is condensed into is condensed into a more compact form known as a chromosome.. In the case of humans we have 23 chromosomes. As it is still preparing to divide, the chromosomes are still made up of the two chromatids (the original and the copy), joined by a midpoint known as a centromere, giving the typical image of an X.

This is not the only thing that happens; it should be remembered that the genetic material is located inside a nucleusIn order to gain access to it, the membrane that surrounds it must be degraded. In addition, the mitotic spindle is generated, a set of filamentous protein structures (microtubules), which will later act as transport pathways for chromosomes.

2. Metaphase

When these aforementioned microtubules attach to the centromere of the chromosomes and align right in the center of the cell is when metaphase occurs. It is already at the point where the genetic content is separated. This is a rapid phase of mitosis.

3. Anaphase

In this phase of mitosis you will understand how the mitotic spindle acts. What it does is to separate the sister chromatids and drag them to opposite poles, as if they were a fishing rod that is picking up the fishing line. This way you get the same genetic content in the two new cells.

4. Telophase

Once on opposite sides, the chromosomes are decondensed into their usual shape and the nucleus containing them is regenerated. Cytokinesis, i.e. the splitting into two cells, takes place at the same time.. This process begins at the end of anaphase, and consists in the case of animal cells in a contractile ring that strangles the cell membrane more or less through the center, as if it were a balloon, until two independent cells are generated.

The end result of mitosis is the formation of two sister cells in interphase, since they contain the same genetic content and there has been no modification of this, it has simply been replicated. It should be noted that any abnormality in this process stops it immediately.