Mitosis Cell Division: Stages, Purpose, and Importance

The cell division is a process in which a single cell divides to form two or four daughter cells. Mitosis and meiosis is the two types of cell division.

Mitosis is a process of the cell cycle in which the division of pre-existing cells produces two identical daughter cells. During mitosis, replicated chromosomes separates into two daughter nuclei containing equal amounts of genetic information. On account of this, mitosis is also known as equational cell division.

Stages of Mitosis Cell Division

Howard and Pele (1953) have divided the cell cycle into G1, S, G2, and M phases. G1 phase, S phase, and G2 phase are combined in the interphase.

Interphase 

It is the longest phase in the cell cycle, where the daughter cell starts preparing before the mitosis phase (M-phase) begins. It has three stages;

1. G1 phase:

• This phase is also known as the resting phase, first gap phase, or first growth phase.
• DNA synthesis does not take place.
• It involves the synthesis of RNA, protein, and membranes needed for the development of cytoplasm and nucleus of daughter cells.

2. S phase:

• Also known as S-phase or synthetic phase
• It involves the synthesis of histone protein (needed for replication), and two DNA molecules are formed by replication.

3. G2 phase:

• Also known as the second gap or growth phase, or resting phase of interphase
• The phase where DNA synthesis ends and the prophase stage initiates
• Continuous synthesis of RNA and proteins that is required for cell growth takes place.

https://www.youtube.com/watch?v=RNwJbMovnVQ

Mitotic phase or M-phase 

It is the short period of chromosome condensation, separation, and cytoplasmic division. This phase initiates at the point of interphase (G2 phase). It is divided into the following phases;

1. Prophase (Pro= Before; Phasis= Appearance): It is the first stage of M-phase. The feature visible in prophase are:

• The appearance of a thin-thread-like condensing chromosome containing two chromatids held together by the centromere marks the first phase of mitosis, called prophase.
• The cell begins the process of division.
• The nuclear envelope disappears.
• Formation of the spindle or mitotic apparatus in the cytoplasm takes place.

2. Prometaphase:

• The nuclear envelope’s disappearance marks the prometaphase’s initiation and enables the mitotic spindle to interact with the chromosome.
• The spindle appears to be aligning the chromosomes at the metaphase plate is the characteristic feature of the stage.
• Microtubules attach to the kinetochore; balanced bipolar force holds the chromosomes on the metaphasic plate.

3. Metaphase: It is the second step of mitosis where the nucleus dissolves and the chromosomes thicken and align at the center of the cell. The characteristic properties seen in cell during metaphase are:

• Chromosomes are the shortest and thickest. So, can be distinctly visible under microscope.
• Centromeres occupy the plane of the equator of the mitotic apparatus (equatorial or metaphasic plate)

4. Anaphase

• It begins precipitously with the synchronous splitting of each chromosome into its sister chromatids called daughter chromosomes with one kinetochore.
• After separation, each chromosome moves toward the opposite pole. As the microtubules of the mitotic spindle pull chromosomes, they appear V-shaped.

5. Telophase

• The end of the polar migration of daughter chromosomes marks the beginning of the telophase.
• Each separated daughter chromosome resumes their long, slender, extended 
• form as their coils relax
• Nuclear envelopes reunify around each group of chromosomes to form daughter nuclei.
• Mitotic apparatus except the centrioles disappears.
• Telophase is followed by cytokinesis, constricting the cytoplasm into two separate cells.

Purpose/Significance of mitosis 

• To maintain proper size of the cell
• To maintain equilibrium in quantity of RNA and DNA  in the cell
• To restore old or dead cells of the body
• In some organisms, it is involved in asexual reproduction
• Provides opportunity for the growth or development of organs and the body of individuals
• Maintains equal distribution of chromosome to each daughter cell with pure genome as recombination or crossing over does not take place in mitosis.
• Embryogenesis and blastogenesis both involves mitosis
• Gonads and sex cells undergo mitosis in order to increase their number.

References

1. Mitosis/ cell division/ Scitable. Scitable. Retrieved 23rd July 2022, from https://www.nature.com/scitable/definition/mitosis-cell-division-47/
2. Mitosis- equational division. BYJU’S learning App. Retrieved 22nd July2022, from https://byjus.com/biology/mitosis/
3. What is mitosis? yg Topics. Retrieved 24th July 2022, from https://www.yourgenome.org/facts/what-is-mitosis/
4. Verma Ps and Agrawal VK (2008). cell biology, genetics, molecular biology, evolution and ecology. Ram nagar, New Delhi: S.Chand & Company Pvt.Ltd. https://books.google.com.pk/books?id=RXscEAAAQBAJ&printsec=frontcover#v=onepage&q&f=false