“Mitosis is that step in the cell cycle where the newly formed DNA is separated and two new cells are formed with the same number and kind of chromosomes as the parent nucleus.”
This is a process of asexual reproduction in unicellular organisms. Read on to explore what is mitosis, and the different stages of mitosis.
What is Mitosis?
Cell division is the driving process of reproduction at the cellular level. Most eukaryotic cells divide in a manner where the ploidy or the number of chromosomes remains conserved, except in the case of germ cells where the number of chromosomes is halved.
Mitosis is the phase of the cell cycle where the nucleus of a cell is divided into two nuclei with an equal amount of genetic material in both the daughter nuclei. It succeeds the G2 phase and is succeeded by cytoplasmic division after the separation of the nucleus.
Mitosis is important for the growth of the cells and for the replacement of worn out cells. Mistakes made during mitosis might result in changes in the DNA that cause genetic disorders.
Features of Mitosis
- In each cycle of cell division, two daughter cells are formed from the parent cell.
- The cell is also known as equational cell division because the chromosome number in the parent cell and daughter cell is the same.
- In plants, mitosis leads to the growth of vegetative parts of the plant like root tip, stem tip, etc.
- Segregation and combination do not occur in this process.
The processes occurring during mitosis have been divided into different stages.
Stages of Mitosis
Right before prophase, the cell spends most of its lifetime in the interphase, where preparations are made before the beginning of mitosis (the DNA is copied). However, since the actual process involves the division of the nucleus, prophase is technically the first stage of this process.
The different stages of mitosis occurring during cell division are given as follows-
Before entering mitosis, a cell spends a period of its growth under interphase. It undergoes the following phases when in interphase:
G1 Phase: This is the period before the synthesis of DNA.
S Phase: This is the phase during which DNA synthesis takes place.
G2 Phase: This is the phase between the end of DNA synthesis and the beginning of prophase.
Prophase immediately follows S and G2 phase of the cycle and is marked by condensation of the genetic material to form compact mitotic chromosomes composed of two chromatids attached at the centromere.
The completion of prophase is characterized by the initiation of the assembly of the mitotic spindle, the microtubules, and the proteinaceous components of cytoplasm that help in the process.
The nuclear envelope starts disintegrating.
In the prometaphase, the nuclear envelop disintegrates. Now the microtubules are allowed to extend from the centromere to the chromosome. The microtubules attach to the kinetochores which allow the cell to move the chromosome around.
At this stage, the microtubules start pulling the chromosomes with equal force and the chromosome ends up in the middle of the cell. This region is known as the metaphase plate. Thus, each cell gets an entire functioning genome.
The onset of anaphase is marked by the splitting of the sister chromatids. These sister chromatids become the chromosome of the daughter nuclei. The chromosomes are then pulled towards the pole by the fibres attached to the kinetochores of each chromosome. The centromere of each chromosome leads at the edge while the arms trail behind it.
The chromosomes that cluster at the two poles start coalescing into an undifferentiated mass, as the nuclear envelope starts forming around it. The nucleolus, Golgi bodies and ER complex, which had disappeared at the completion of prophase start to reappear.
Telophase is followed by cytokinesis, which denotes the division of the cytoplasm to form two daughter cells. Thus, it marks the completion of cell division.
Also Read: Cell Cycle
Functions of Mitosis
Following are the two important functions of mitosis:
- Mitosis helps in the development of an organism. In single-celled organisms, mitosis is the process of asexual reproduction.
- Mitosis helps in the replacement of damaged tissues. The cells near the damaged cells begin mitosis when they do not sense the neighbouring cells. The dividing cells reach each other and cover the damaged cells.
Significance of Mitosis
- Mitosis is responsible for the development of the zygote into an adult.
- The chromosomes are distributed equally to the daughter cells after each cycle.
- It is responsible for a definite shape, and proper growth and development of an individual.
- It maintains the constant number of chromosomes in all body cells of an organism.
- In plants, mitosis helps in the formation of new parts and in the repairing of damaged parts. Mitosis helps in vegetative propagation of crops also.
- Since no recombination and segregation occurs in the process, it helps in maintaining the purity of types.
- It helps in maintaining a balance between the DNA and RNA contents as well the nuclear and cytoplasmic contents of the cell.
- It is responsible for replacing dead and old cells in the animals. Eg., gut epithelium, and blood cells.
Also Read: Difference Between Mitosis And Meiosis
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Frequently Asked Questions
What is Mitosis?
Mitosis is a type of cell division that results in the development of two daughter cells, each possessing the same type and number of chromosomes as their original parent nucleus. This type of cell division is observed in non-sex cells, essentially growing body parts and repairing damaged tissues.
Name the 4 stages of mitosis.
The 4 stages of mitosis are:
What is prophase?
The process of mitosis begins with the prophase. In this stage, the chromatin condenses and the nucleolus disappears.
What happens in metaphase?
The second stage of the process, the parent cell contains chromosomes that are condensed and present at the equator, before being split apart for each of the two daughter cells.
The anaphase is marked by the splitting of the sister chromatids. Eventually, these sister chromatids become the chromosome of the daughter nuclei.
List the events of telophase.
The final stage of mitosis, telophase involves the now spilt sister chromatids reaching the polar ends. The nuclear envelope starts forming along with the other cell organelles such as the Golgi bodies and ER complex.
In what cells does mitosis occur?
Mitosis occurs in eukaryotic cells. Eukaryotic cells divide by both mitosis and meiosis. For eg., skin cells divide by mitosis whereas gametes divide by meiosis.
What is the main function of mitosis?
Mitosis plays an important role in the life cycle of most living things. It helps in cell regeneration, asexual reproduction, and growth.