We explain what is the cellular division or cell division, meiosis, mitosis and its phases. In addition, its importance for the diversity of life.
What is cell division or reproduction?
It is known as cell reproduction or cell division at the stage of the cell cycle in which each cell divides to form two different daughter cells . This is a process that occurs in all life forms and guarantees the perpetuity of its existence, as well as growth, tissue replacement and reproduction in multicellular beings.
The cell is the basic unit of all known life . Each of them, like living beings, has a life time , during which they grow, mature and then reproduce , through various biological mechanisms that allow new cells to be generated , replicating their genetic information and allowing the cycle to return to start.
This occurs until, at a certain point in the life of living beings , their cells stop reproducing (or doing so efficiently) and begin to age. But until that happens, cell reproduction has the purpose of increasing the amount of cells that exist in an organism .
In the case of unicellular organisms , create a totally new organism . This generally occurs when the cell size has reached a certain size and volume, which usually decrease the effectiveness of its nutrient transport processes and, thus, the division of the individual is much more effective.
Main Types of cell division or reproduction
In principle, there are three major types of cell reproduction. The first and simplest is the binary fission , where the genetic material of the cell replicates and it proceeds to split into two identical individuals , as do the bacteria , equipped with a single chromosome and reproduction processes asexual
However, in more complex beings such as eukaryotes , equipped with more than one chromosome (such as humans , for example, that we have a pair of chromosomes of each type: one of the father and one of the mother), processes are applied more complicated cell reproduction that we will see separately:
- Mitosis . It is the most common form of cell division of eukaryotic cells. In this process the cell replicates its genetic material completely, using a method of organization of the chromosomes in the equatorial region of the cell nucleus , which then proceeds to divide into two, generating two identical twins. Then the rest of the cell proceeds to duplicate and slowly cleave the cytoplasm , until the plasma membrane ends up dividing the two new daughter cells into two. The results will be genetically identical to their parent.
- Meiosis . This is a more complex process, which produces haploid cells (with half the genetic load), such as sex cells or gametes, endowed with genetic diversity. This in order to provide half of the genomic load during fertilization, and thus obtain genetically unique offspring, avoiding clonic (asexual) reproduction. For this, a diploid cell (2n) undergoes a series of two consecutive divisions, thus obtaining four haploid daughter cells (n).
- Silent divisions: Silent splits are splits without mutations . They are sometimes confused with mutations that are not detectable. But you can check if the divisions are silent by comparing the frequencies of the alleles of the cell line, with the sum of the frequencies of the alleles of the two derived cells, which has to be similar. A division that results in a cell without mutations (silent) and a dead cell (which does not contribute to the adult) cannot be detected.
Types of reproduction associated with cell division
Bipartition : is the division of the stem cell into two daughter cells, each new cell is a new individual with structures and functions identical to the stem cell. This type of reproduction is presented by organisms such as bacteria , amoebas and algae .
Budding : it occurs when new individuals are produced from buds. The budding process is frequent in sponges , coelenterates and bryozoans . In one or more areas of the parent organism an envagination or bud is produced that develops and at a certain moment suffers a constriction at the base and separates from the parent, beginning its life as a new being. The daughter buds may have other buds which are called secondary buds.
In some organisms colonies can form when the buds do not separate from the parent organism. In the most evolved forms of bryozoans, it is observed in the budding process that it is carried out in a more complicated way. Budding is the evolutionary process of the living being by meiosis. The number of individuals in a colony, the way they are grouped, and their degree of differentiation varies and is often characteristic of a given species. The bryozoans can originate new individuals on some extensions called stolons and the process is called stolonization .
Certain species of animals can have internal budding, buds that survive in unfavorable conditions, thanks to a protective envelope. In the case of freshwater sponges , the buds have a protective capsule and there is a reserve substance inside. When spring arrives, the protective capsule is lost and the new sponge emerges from the bud. In freshwater bryozoans a layer of chitin and calcium is produced and they do not need a reserve substance as they are in a state of hibernation .
Sporulation : sporogenesis or sporogenesis consists of a process of cellular differentiation to reach the production of resistance dispersive reproductive cells called spores . This process occurs in fungi , amoebas , lichens , some types of bacteria , protozoa , sporozoa (such as the malaria- causing Plasmodium ), and is frequent in vegetables (especially algae , mosses and ferns), groups of very different evolutionary origins, but with similar reproductive strategies, all of them can resort to the formation of resistance cells to promote dispersal. During sporulation, the nucleus is divided into several fragments, and by asymmetric cell division a part of the cytoplasm surrounds each new nucleus, giving rise to spores. Depending on each species, an appreciable number of spores can be produced and from each of them an independent individual will develop.
Cell division is the process by which cellular material divides between two new daughter cells. In unicellular organisms this increases the number of individuals in the population. In multicellular plants and organisms, it is the procedure by which the organism grows, starting from a single cell, and damaged tissues are also replaced and repaired.
Other types of reproduction
The most common form of division gives rise to two equal daughter cells, so it is said to be a bipartition or binary division. But there are variations that generally affect the mode of cytoplasm division ( cytokinesis ) or the mode of duplication and distribution of chromosomes (amitosis). They occur mainly in unicellular beings, where cell reproduction is equivalent to the reproduction of the organism. We will emphasize the following types:
- Multipartition or multiple division . The pluripartición occurs in cells that divide often your core without initially split their cytoplasm, which originate cells plurinucleadas. Later cytoplasmic division or cytokinesis occurs , which gives rise to several daughter cells, each with its own nucleus. It is typical of some protozoa.
- Germination . In germination the daughter cell originates from a small bulge or yolk on the surface of the stem cell to which the nucleus is directed, which divides and separates from the stem cell by a membrane surrounding the nucleus and cytoplasm of the yolk, while the daughter cell grows. It is typical of how yeast Saccharomyces cerevisiae , in which the daughter cells remain attached to the stem for a time, and can form chains if the process is repeated ( mycelia of budding). When the cell comes off it leaves a budding scar or scar on the stem cell, in which dozens of marks can be observed.
- Asexual reproduction of certain animals, such as cnidarians , sponges, and bryozoans , in which a yolk that appears on the body of the initial individual, grows to form a new individual, is also called budding ; but this is a mode of asexual reproduction of the animal rather than a type of cell division.
- Sporulation . The sporulation occurs in some protozoa , which at certain times of their life cycle in stem cell surrounds a tough cover the island from abroad. Then the nucleus divides several times and originates inside the mother cell several daughter cells. When the stem of the stem cell breaks, the daughter cells or spores come out, which, under favorable conditions, disintegrate and give rise to normal vegetative cells.
- Spore formation is also called spore formation of pteridophyte , bryophyte, and fungal plants . In this case it is a type of asexual reproduction of the whole organism through the release and subsequent germination of spores. Bacteria can also form resistance endospores , which is a form of entanglement rather than division.
- Amitose . The amitose is a different kind of division of mitosis. In amitosis the nucleus divides by constriction, with no condensation of chromatin into chromosomes or any of the phases or morphogenetic changes typical of mitosis. The distribution of chromosomes in cells appears to be random, so it would not ensure that daughter cells carry the same number of chromosomes. It typically occurs in ciliated protozoa with polyploid macronucleus with vegetative functions and diploid micronucleus with reproductive functions, as part of their life cycle. In the micronucleus the division is by mitosis and the distribution of chromosomes between the daughter cells is exact, but in the macronucleus the division is done by amitosis.
- There is also talk amitose playback abnormal pathological certain cells in man and other mammals. But also observed amitosis in normal cells, like the adrenal and other. In pine irradiated Chenobil (Ukraine) also observed cases amitose.
Phases of reproduction
In mitosis-like cell reproduction, we find the following phases:
- Interface : The cell prepares for the reproduction process, duplicating its DNA and taking the pertinent internal and external measures to successfully face the process.
- Prophase : The nuclear envelope begins to break (until it dissolves gradually). The centrosome is doubled and each one moves to one end of the cell, forming microtubules.
- Metaphase : The chromosomes line up in the equator of the cell. Each of them has already doubled in the interface, so at this time the two copies are separated.
- Anaphase : The two groups of chromosomes (which are identical to each other) move away thanks to the microtubules.
- Telophase : Two new nuclear envelopes are formed.
- Cytokinesis : The plasma membrane strangles the cell and divides it into two.
On the other hand, in the reproduction of the meiosis type, we then proceed to a new bipartition of the daughter cells, in order to obtain four haploid cells.
- Importance of cell reproduction
The cell division creates colonies of unicellular organisms, but above all it allows the existence of multicellular organisms , constituted by differentiated tissues. Each tissue is damaged, ages and eventually grows, requiring replacement cells from old or damaged, or simply new cells to add to growing tissue.
That is to say that cell division makes possible both the growth of organisms and the repair of damaged tissues .
On the other hand, disordered cell division can lead to diseases such as cancer , in which this process occurs uncontrollably, threatening the very life of the individual. That is why in modern medicine the study of cell division is one of the key areas of scientific interest.