The 4 phases of mitosis: this is how the cell duplicates

The cell is the unit of life. Probably, one of the fundamental characteristics of these is the capacity that these living beings have when it comes to self-reproduction.

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

• Related article: "Differences between mitosis and meiosis"

The common phase

Cells follow the pattern of a sequential process that ends in cell division. This process is known as the cell cycle. In short, the cycle consists of preparing the cell for its imminent partition of two. This process has traditionally been divided into two major phases: the interface and the M phase. The latter would properly be the phase of mitosis. The interface is shared in both mitosis and meiosis.

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

The interface, in general, is divided into three stages:

• G1 phase (Gap1): the cell grows in size and is metabolically active.
• S phase (Synthesis): the cell replicates its DNA.
• G2 phase: 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 in the division process, unless its DNA is found to be 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 major problems. If all is well, the cell is ready for its imminent proliferation.

Phases of mitosis

After finishing the interface, the cell enters the M phase with the goal 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 the chromosomes, the formation of the mitotic spindle and the union of the 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 M Phase, the replicated DNA that is tangled condenses 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 copy), joined by a midpoint known as the centromere, giving the typical image of a X.

Not only does this happen; remember that genetic material is found inside a nucleus, and in order to access it, the membrane that surrounds them must be degraded. In addition, the mitotic spindle is generated, a set of filamentous protein structures (microtubules), which will later act as transport routes for the chromosomes.

• You may be interested: "Differences between DNA and RNA"

2. Metaphase

When these mentioned microtubules bind to the centromere of chromosomes and they line up right in the center of the cell is when the metaphase occurs. You are already at the point where the genetic content separates. It is a phase of mitosis that is rapid.

3. Anaphase

In this phase of mitosis you will understand how the mitotic spindle works. What it does is separate the sister chromatids and drag them to opposite poles, as if they were a fishing rod that is catching the line. Thus, it is possible to have the same genetic content in the two new cells.

4. Telophase

Once on opposite sides, the chromosomes decondense in their usual way and the nucleus that contains them regenerates. Along with this, cytokinesis occurs, that is, the partition into two cells. 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 in the center, like a balloon, until two cells are generated independent.

The final result of mitosis is the formation of two sister cells in interface, 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 anomaly in this process stops it immediately.