The human body is made up of 37 trillion cells. Surprisingly, this immense amount comes from a single cell conceived during fertilization. This is made possible by the ability of cells to self-reproduce, a process that involves dividing them in half. Gradually, it is possible to achieve the above-mentioned amount, forming the different organs and cell types.
However, there are two basic mechanisms by which cells can reproduce: mitosis and meiosis. Below we will see the differences between mitosis and meiosis and their characteristics.
Mitosis and meiosis
We have seen that little by little, a few cells can give birth to an entire organism, whether it is a human being or a huge whale. In the case of human beings, they are diploid eukaryotic cellsIn other words, they have one pair per chromosome.
The structure of the chromosome is the most compact and condensed form that DNA can present with structural proteins. The human genome is made up of 23 pairs of chromosomes (23×2). This is an important fact to know one of the main differences between mitosis and meiosis, the two classes of cell division that exist.
The eukaryotic cell cycle
Cells follow a series of patterns sequentially for their division. This sequence is called the cell cycle and consists of the development of four coordinated processes: cell growth, DNA replication, distribution of duplicate chromosomes and cell division. This cycle differs at times between prokaryotic (bacterial) or eukaryotic cells, and even within eukaryotes there are differences, for example between plant and animal cells.
The cell cycle in eukaryotes is divided into four stages: G1 phase, S phase, G2 phase (all grouped together in the interphase), G0 phase and M phase (mitosis or meiosis).
This group of steps aims prepare the cell for its imminent partition in two, By following the following phases:
- Phase G1 (Gap1): Corresponds to the gap between a successful division and the start of replication of genetic content. During this phase, the cell is constantly developing.
- Phase S (synthesis): This is when DNA replication occurs, ending with an identical duplicate of genetic content. In addition, chromosomes with the most famous silhouette (X-shaped) are formed.
- Phase G2 (Gap2): It continues with cell growth, in addition to the synthesis of structural proteins that will be used during cell division.
Throughout the interface there are several checkpoints to verify that the process is executed correctly and that there are no errors (for example, that there is no bad duplication). Faced with any problem, the process stops and an attempt is made to find a solution, for cell division is a vital process; everything must be fine.
2. Phase G0
Cell proliferation is lost when cells specialize so that the growth of the organism is not infinite. This is possible because cells enter a resting phase called the G0 phase, where they remain metabolically active but do not show cell growth or replication of genetic content, i.e. they do not continue in the cycle. cellular.
3. Phase M
At this point, it is correct when cell partition occurs and mitosis or meiosis is developing well.
The differences between mitosis and meiosis
In the division phase, there is mitosis or meiosis.
This is the typical cell division of a cell giving rise to two copies. As with the cycle, mitosis has also traditionally been divided into different stages: prophase, metaphase, anaphase, and telophase. Although for a simpler understanding, I will describe the process in general and not for each phase.
At the start of mitosis, the genetic content is condensed in the 23 pairs of chromosomes that make up the human genome. At this point, the chromosomes are duplicated and form the typical x-ray image of chromosomes (each side is a copy), joined in two by a protein structure known as a centromere. The nuclear membrane that closes DNA breaks down so that the genetic content is accessible.
During phase G2, different structural proteins were synthesized, some in two parts. They are called centrosomes, Which are each placed at an opposite pole from each other of the cell.
Centrosomes extend the microtubules, protein filaments that make up the mitotic spindle and bind to the chromosomal centromere, to stretch one of the copies to one side, Break the structure in X.
Once on either side, the nuclear envelope is reformed to close the genetic content, while the cell membrane is strangled to generate two cells. The result of mitosis is two sister diploid cells, Since its genetic content is identical.
This type of cell division it occurs only in the formation of gametes, Which in the case of humans are sperm and ova, cells responsible for the formation of fertilization (these are the so-called germ cell lineage). Simply put, it can be said that meiosis is like performing 2 consecutive mitoses.
During the first meiosis (meiosis 1), a process similar to that explained in mitosis occurs, except that homologous chromosomes (the pair) can exchange fragments with each other by recombination. This does not happen in mitosis because they never come into direct contact, unlike in meiosis. It is a mechanism that offers more variability to genetic inheritance. Outraged, what separates are homologous chromosomes, not copies.
Another difference between mitosis and meiosis occurs with the second part (meiosis 2). Having formed two diploid cells, these are immediately redistributed. Now the copies of each chromosome are separated, so the end result of meiosis is four haploid cells, as they only have one chromosome from each (not pairs), to allow for new matings. to form between fertilization of parent chromosomes and enrich genetic variability.
In order to collect the differences between mitosis and meiosis in humans, we will say that the end result of mitosis is two identical cells with 46 chromosomes (pairs of 23), while in the case of meiosis it is four cells. chromosomes each (without pairs), in addition to which their genetic content can vary by recombination between homologous chromosomes.