Cell Division – Cell division is the process when a cell divides into two or more. In 1858, a German doctor named Rudolf Virchow put forward a theory about cells, namely “omnis cellula e cellula” .
That is, each cell comes from other cells, so cells have the expertise to divide or reproduce themselves. Then, how can cells divide? Biologists distinguish the process of self-division into three types, namely amitosis, mitosis, and meiosis. See a more complete explanation of cell division below, Sinaumed’s. Check these out!
A. Definition of Cell Division
Cell division is an event where a cell divides into two or more to become new cells. Cell division is a way for cells to reproduce themselves or what is called reproduction. The cell is the smallest part that makes up the body of a living thing.
The growth and development of living things is closely related to this process of cell division. However, the function of cell division in multicellular and unicellular living things is very different even though the essence is the same, namely cell multiplication. Cell division is very important for the survival of all beings. Cells themselves undergo division to:
- Growth : Living things can grow because their cells multiply. The more cells in a living thing, the bigger the size of that living thing.
- Repair: When the body is injured, after some time the injured body part will close as before. In the injured part of the body, tissue damage actually occurs. Repair of tissue damage in the body is the result of the process of cell division.
- Reproduction or breeding: One of the characteristics of living things is to reproduce to preserve their offspring by giving birth, laying eggs, and so on.
In studying cell division and the development of other living things, you can use the Cell Molecular Biology book as a reference because it will explain various information about cells that you should know.
B. Function of Cell Division
Unfortunately, these cells do age. Like red blood cells that can only live for 120 days and will die after 120 days. This is where the role of cell division is, namely replacing cells that have died or been damaged.
In an adult organism, the number of cells in each organ must be kept constant. That is, there should not be an organ with an excess or decrease in the number of cells.
For example, the number of red blood cells in an adult woman’s body ranges from 4-5 million cells in one microliter of blood. If the number of cells in the body’s organs exceeds the number that should be, a disorder called a tumor will occur.
- The function of cell division in unicellular or single-celled living things is as a way to reproduce. Examples of living things that reproduce by dividing include Protozoa, Amoeba, and others.
- The function of cell division in multicellular living things or multi-celled living things is as a way of multiplying body cells so that the living things concerned can grow and develop. Cells that divide are called parent cells, while cells that result from division are called daughter cells. Basically the process of cell division is divided into direct cell division and indirect cell division.
The process of cell division is a way for cells to grow and develop. Cells that divide are called parent cells, while cells that result from division are called daughter cells. Basically the process of cell division is divided into 2, namely: direct cell division and indirect cell division.
C. Types of Cell Division
According to the cell theory, all living cells come from pre-existing cells (omnis cellula e cellula) . This theory was stated by Rudolf Virchow in 1855.
In studying the various types of cells that exist and how they function in the body, Sinaumed’s can read the All Cells book below.
The formation of new cells or daughter cells from pre-existing cells can occur through the process of cell division. There are two types of cell division, namely mitosis and meiosis. These two types of reproduction will be explained in detail as follows:
Mitotic division occurs in body cells (somatic cells) of living things. In this division, daughter cells are produced which have the same number of chromosomes as the parent cell.
Mitotic division is a type of cell division that produces 2 daughter cells. These daughter cells are genetically identical to the parent cell.
This means that the two daughter cells formed have the same genetic makeup, including the same number of chromosomes as the parent. The number of chromosomes possessed by daughter cells is 2n or is called diploid. Diploid cells are cells with paired chromosomes (2n).
Mitosis is a process of cell division that produces two daughter cells, each of which has the same characteristics and number of chromosomes as the parent cell.
This division itself aims to replace or repair body tissue that has been damaged or worn out. Growth is to multiply cells so that both the quantity and quality increase.
It forms a network because the product of this division is the chromosomes or the nature of the parent is the same as the nature of the offspring, meaning that because it forms a network, both new and old cells are the same.
Mitotic division has a character: it takes place in somatic cells to produce 2 daughter cells that are identical to the parent. They divide once. One division with the second is interspersed with interphase (rest does not divide).
The daughter cells have the same number of chromosomes as the parent, have the same characteristics as the parent, have the ability to divide again, this does not occur in the daughters resulting from meiosis.
In organisms it can occur at a young age, in adulthood, or in old age, in which the division of meiosis can only occur in adulthood, not in organisms that are young.
The stages are IPMAT interphase first, then PMAT again. Mitotic division is a continuous process consisting of five phases, namely:
The longest division phase in which the cell is preparing for synthesis of proteins, lipids, and others. The centrioles then invade the nucleus. Microfilaments extend from the base of the centrioles and attach to chromatin at the kinetochores.
At this stage the nucleolus and nuclear envelope begin to disappear. In this phase, the stem cell that is about to divide shows symptoms of the formation of two centrioles from the centrosome, one of which remains in place, while the other moves towards the opposite pole.
Each centriole emits fibers in the form of filaments called cleavage spindle threads (spindle threads), which connect the centrioles to one another. The nuclear membrane, which is still visible in the early prophase, is soon fragmented.
Chromatin granules elongate into chromatin threads. The chromatin threads then shorten and condense into chromosomes, with the contiguous portion called the centromere.
The centromere is the part of the chromosome that cannot absorb dye. Each centromere contains a kinetochore, which is where microtubules attach. Furthermore, the chromosome is duplicated longitudinally into two parts, each of which is called a chromatid. Simultaneously, the nucleus (nucleolus) shrinks and is not visible or disappears.
Thus, the chromatids of the spindle fibers extend outwards in all directions, referred to as asters. At the end of pophase, the nuclear envelope ruptures and each chromatid attaches to several spindle fibers at the kinectors. Duplicated chromosomes then leave the polar regions and align at the equator. In plant cells that do not have centrioles, the spindle threads of division are formed between two points called the poles.
Chromatin that has become chromosomes gathers at the nuclear equator, the nucleolus then breaks into granules.
The most rapid part in which the cell is pulled to the two polar bodies by the two centrioles.
End of division in which the cell divides into two and separates along with the division of cell organelles which then occurs cytokinesis (division of the cytoplasm) at that stage.
This phase is an intermediate phase which is a period between one mitosis and another. this phase is not a resting phase, but a phase in which active cell metabolism is carried out. In the interphase phase, cells will experience three stages, namely the Primary Growth Phase (Gap 1 or G1), the Synthesis Phase (S) and the Secondary Growth Phase (Gap 2 or G2).
2. Division of Meiosis
Meiosis division only occurs in the sex organs, meiosis division functions to produce gamete cells (egg cells and sperm cells). Through this division will produce daughter cells that have half the chromosomes of the parent cell. Meiosis is a cell division that produces 4 daughter cells, each of which has half the number of chromosomes as the parent cell.
The number of chromosomes owned by daughter cells is n or is called haploid. Thus, meiotic cell division is known as reduction division. The phases of meiosis are similar to those of mitosis. Meiosis division takes place in 2 stages, namely meiosis I and meiosis II.
a. Meiosis I phase
This phase begins after the replication of the parent chromosome to produce identical chromatids in S phase. At the start of prophase I, the chromosomes shorten, thicken, and duplicate.
Then in the middle of prophase I, the centrosomes move to opposite poles. Chromosomes also carry out crossing over or crossing over. At the end of prophase I, the ends of the spindle fibers attach to the two kinetochores. In prophase I there are also various stages, namely leptotene, zygotene, pakitene, diplotene, and diakinesis.
Leptotene is the process by which chromatin shortens and thickens to form homologous chromosomes. Zygotene occurs when homologous chromosomes come close together and pair up.
The next stage is pachytene, namely the occurrence of doubling or replication of chromosomes. Then, there is a diplotene or crossing over and the place of crossing between the two chromosome arms is called a chiasm. Finally is the stage of diakinesis, which is when the spindle or spindle threads are formed.
b. Meiosis II phase
This phase is the second cycle of the process of meiosis and is similar to the process of mitosis. The difference is that cells that undergo division are haploid, not diploid. In this phase II, the number of chromosomes is kept constant during sexual reproduction. This process also results in genetic variation due to crossing.
3. Amitotic division
Amitotic division generally occurs in unicellular organisms, namely organisms composed of only one cell such as bacteria and cyanobacteria. Amitotic division is a spontaneous division in which the cell immediately divides into two. Occurs spontaneously because unicellular organisms such as bacteria and cyanobacteria are prokaryotic cells that do not have a nuclear membrane.
Therefore, cell division can occur directly because there is no nucleus to divide. How do bacterial and cyanobacterial cells divide?
- The first step, the chromosomes in bacteria or cyanobacteria must multiply first. The trick is to stick to the plasma membrane and carry out a doubling process called duplication.
- At the same time, the bacterial or cyanobacterial cell also elongates and the center bends inward, dividing the cell into two.
- After that, each chromosome will be divided into each new cell candidate.
- Finally, a partition will form and the two candidate cells will separate. Finally, the bacterial cell becomes two cells that are exactly the same with the same number of chromosome arrangements which is called the daughter cell, while the initial cell that forms the two daughter cells is called the parent cell. In contrast to bacteria and cyanobacteria, multicellular organisms such as animals, plants and humans, have eukaryotic cells and have a cell nucleus. Thus, it must begin with the division of the cell nucleus first. This is what happens in mitosis and meiosis.
D. Examples of Cells Undergoing Mitosis and Meiosis
The process of cell division is carried out to form new cells, these cells will form tissues to organs. However, these cells have a lifespan that can die, for example red blood cells which only live for 120 days.
This is the reason why the process of cell division must be carried out by cells to replace dead or damaged cells. Especially in adult organisms, they must have a constant number of cells.
It should be noted that if the number of cells decreases, it will cause disease in the body of the living creature concerned. This is very important for the continuation of the life of the organism.
For example, an adult woman has about 4-5 million red blood cells in one microliter of blood. If the amount is excessive it will cause a tumor. In short, mitotic division is a division process that goes through several phases.
The division path starts from the protase phase, metaphase, anaphase and telophase. This process occurs in somatic cells, with the aim of growth, chest regeneration and wound closure. The result of mitotic division is in the form of two offspring that are identical to their parents.
The human body itself consists of millions of cells that can only be seen using a microscope. A complete explanation of cells in the human body can be studied by Sinaumed’s in the book Bio Series: Cells.
Mitosis occurs in somatic cells, body cells in both plants, animals and humans. Examples of mitotic divisions include root cells, stem cells, leaf cells, skin cells, liver cells, epithelial cells, and other somatic cells.
In contrast to mitotic division, meiotic cell division goes through more complex stages. Where there are 2 cell divisions, namely Meiosis I and Meiosis II, in the process there is no interphase phase.
In short, mitotic division is a division process that goes through several phases. The division path starts from the protase phase, metaphase, anaphase and telophase.
This process occurs in somatic cells, with the aim of growth, chest regeneration and wound closure. The result of mitotic division is in the form of two offspring that are identical to their parents. Mitosis occurs in somatic cells, body cells in both plants, animals and humans.
Examples of meiotic divisions include root cells, stem cells, leaf cells, skin cells, liver cells, epithelial cells, and other somatic cells. In contrast to mitotic division, meiotic cell division goes through more complex stages. Where there are 2 cell divisions, namely Meiosis I and Meiosis II, in the process there is no interphase phase.
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