Stages mitosis or cell division begins with interphase and mitotic division. Interphase covers 90% of the cell cycle. This phase is useful for making interlocking chromosomes in preparation for mitotic division. To find out in full, here is a step-by-step explanation: mitosis.
Also Read: Definition, Examples, and Characteristics of Mitosis
Interface
In interphase, there is a process of preparation and storage of energy by cells for division. During interphase, the cell nucleus (nucleus) and daughter cell nucleus (nucleolus) are clearly visible. However, the chromosomes in the cells are not visible because they are still in the form of chromatin. Chromatin is fine threads composed of DNA, RNA, and protein molecules.
On the outside of the cell nucleus is the centrosome. Centrosome is a cell organelle that has a function to maintain the number of chromosomes between parent cells and daughter cells to remain the same throughout life cell division. If in an animal cell, each centrosome will contain a pair of centrioles shaped like a small cylindrical body
The interphase stage is grouped into three, namely the G1 phase (the first gap), the S phase (synthesis), and the G2 phase (the second gap).
- Phase G1 (First Gap)
The G1 phase is also known as the cell growth and development phase. This phase is characterized by the development of the cytoplasm (cell fluid), cell organelles, and the synthesis of materials to be used. Subphase G-1 is the longest process in interphase, which is about 12-24 hours.
At this stage, the cell grows larger. Some of the growth of cell parts, including:
- There is an increase in the size of the nucleus.
- Increase in cytoplasmic volume.
- DNA formation.
- Formation of enzymes for DNA replication.
- The formation of proteins through the process of protein synthesis (transcription and translation) to stimulate nuclear division.
- Spindle thread formation.
- Phase S (Synthesis)
In the S phase, DNA replication or duplication occurs as genetic material that will be passed on to daughter cells, so that later two copies of DNA will be produced. In the synthesis stage, DNA replication occurs along with histone proteins whose strands are called chromatin threads. This process of replication of chromatin threads forms twins called chromatids. The two sister chromatids are attached to one centromere. The synthesis process at this stage takes about 6 to 8 hours.
- Phase G2 (Second Gap)
The third phase, namely the G2 phase, DNA replication has been completed. There is an increase in protein synthesis as the final stage of cell preparation for division. In the secondary growth stage, cell organelles as well as RNA are formed. This stage takes about 3 to 4 hours and is the last process before the cell is completely ready to divide.
Chromatin in the phases of the cell cycle:
- Double chain DNA.
- Chromatin (single-stranded DNA along with histone proteins).
- Chromatin at interphase (blue) and centromere (red).
- Dense chromatin during prophase.
- Chromosomes in metaphase.
At the end of interphase, one cell already has a nucleus with two nucleoli (child nuclei). As previously explained, in the nucleus there are already chromatids, i.e. chromatin threads that have been duplicated. Meanwhile outside the nucleus, the centrosome is also duplicated and will later help the process of cell separation in the phase mitosis. Furthermore, after all preparations are complete, the cell will enter the phase mitosis which consists of four stages.
Also Read: Complete Explanation of Organelles in Plant Cells
Mitosis in Animals
Mitosis cell division
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Process mitosis produce 2 daughter cells from 1 original cell. Because all cells in the body come from mitosis an egg that has been fertilized then each cell has the same type and number of chromosomes, and with the same number and types of genes.
Speed and frequency cell division vary widely in various tissues and in various animal species. At the stage of embryonic development the distance between cell division maybe only about 30 minutes. In certain mature tissues, especially nerve cells, cell division very rarely.
In other adult tissues, such as the spinal cord, which is where red blood cells are produced, cell division must occur frequently to provide the 10,000,000 red blood cells produced every second of day and night by humans.
- Profase Level
At the beginning of prophase, the centrosome undergoes replication, resulting in two centrosomes. Then, each centrosome will move towards the opposite poles of the cell nucleus. At about the same time, microtubules begin to appear between the two centrosomes. These microtubules are long protein fibers that extend from the centrioles in all directions.
Over time, microtubules will form like threads that we can call spindle threads. At this stage too, the chromatin threads begin to thicken which then form chromosomes. Chromosomes have two identical chromatids attached to the centromere (head of the chromosome). Each centromere has two kinetochores which are protein formations and ultimately become the attachment site for the spindle fibers. At the end of the prophase stage, the nucleus and nuclear membrane of the cell begin to disappear. In addition, the centrosomes have arrived at their respective poles. The spindle threads will also stretch from one pole to another. This spindle thread has a role to pull the chromosomes to the center of the cell nucleus at a later stage. Chromosomes have doubled alias has become 2, then condensed. The nuclear membrane begins to break down into small pieces (fragments)
- Tahap Metafase
At this stage, the nucleus and nuclear membrane of the cell become invisible. Each kinetochore at the centromere is connected to a centrosome by spindle fibers. The pair of chromatids will move to the center of the cell nucleus (equatorial plane) and form the metaphase plate.
The position of the chromosome which is located in the center of the nucleus of this cell produces the number of chromosomes that can be calculated precisely and the shape of the chromosome can also be clearly observed. In this phase, the chromosomes have doubled, then condensed. The nuclear membrane begins to break down into small pieces (fragments)
- Anaphase Stage
This stage is characterized by the separation of chromatids. Starting from the centromere which then forms a new chromosome. Each chromosome is pulled by the spindle fibers moving towards the poles in different directions. The number of chromosomes going to one pole will be exactly the same as the number of chromosomes going to the other pole.
Thus, in the final stage of anaphase, the chromosomes almost arrive at their respective poles. In addition, cytokinesis begins to occur. What is cytokinesis? Cytokinesis is the phase of division or separation of the cytoplasm, organelles, and cellular membranes. This division begins from the edge of the cell (cell membrane) moving towards the center of the cell, so that it will produce two cells called daughter cells. The conclusion of the anaphase stage is that the chromosomes move towards the opposite poles and at the end of anaphase the two poles of the cell have the same number of chromosomes.
Also Read: Complete Description of Organelles in Animal Cells
- Telophase Stage
This stage is the final stage of mitotic fission. At this stage we have entered the final stage of fission mitosis. The chromosomes have arrived at their respective poles. The spindle fibers begin to disappear and the nuclear membrane of the cell also begins to exist between the two separate groups of chromosomes. During this phase, several things happen, including:
- Chromosomes will gradually thin out and change shape into chromatin threads again.
- The nuclear membrane begins to rejoin.
- Two diploid daughter cells are formed.
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