What is Mitosis? Briefly comment on various stages of cell division with suitable diagrams

Mitosis: Definition

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Mitosis is a type of cell division in eukaryotic organisms that results in the production of two genetically identical daughter cells, each with the same number of chromosomes as the parent cell. Mitosis is responsible for growth, development, tissue repair, and asexual reproduction in organisms. It is essential for the maintenance of the chromosome number across generations of cells.

Stages of Mitosis

Mitosis is a continuous process that is divided into several distinct phases. These stages ensure that the cell’s genetic material is accurately duplicated and evenly distributed between the two daughter cells. The stages of mitosis are:

1. Interphase (Preparation for Mitosis)
   • Interphase is not technically part of mitosis but is a crucial preparatory phase that takes place before mitosis begins. It consists of three sub-stages:
     1. G1 phase (Gap 1): The cell grows and carries out its normal metabolic functions.
     2. S phase (Synthesis): DNA is replicated, and each chromosome is duplicated.
     3. G2 phase (Gap 2): The cell continues to grow and prepares for mitosis.
   • After interphase, the cell enters the mitotic phase (M phase).
2. Prophase
   • Chromatin Condensation: In prophase, the chromatin fibers condense into visible chromosomes, each consisting of two identical sister chromatids connected by a centromere.
   • Spindle Formation: The mitotic spindle, a structure made of microtubules, begins to form from the centrosomes. These centrosomes are located at opposite poles of the cell.
   • Nuclear Envelope Breakdown: The nuclear membrane dissolves, allowing the spindle fibers to interact with the chromosomes.
3. Metaphase
   • Chromosome Alignment: In metaphase, the chromosomes align at the metaphase plate, an imaginary line at the cell’s equator. This alignment ensures that the chromosomes will be evenly distributed to the daughter cells.
   • The spindle fibers attach to the centromere of each chromosome, forming the kinetochore, a structure that connects the chromosomes to the spindle.
4. Anaphase
   • Separation of Chromatids: In anaphase, the sister chromatids are pulled apart toward opposite poles of the cell. The centromere splits, and the kinetochore microtubules shorten, separating the chromatids.
   • This ensures that each daughter cell will receive an identical set of chromosomes.
5. Telophase
   • Chromosome De-condensation: Once the chromatids reach the opposite poles of the cell, they begin to de-condense back into chromatin.
   • Nuclear Envelope Reforms: New nuclear membranes form around each set of chromosomes, creating two distinct nuclei within the cell.
   • Spindle Disappears: The mitotic spindle breaks down.
6. Cytokinesis (Final Step of Cell Division)
   • Division of Cytoplasm: Cytokinesis is the process where the cytoplasm and other cell components are divided between the two daughter cells.
   • In animal cells, this is typically achieved through the formation of a cleavage furrow, where the cell membrane pinches inward until the cell is divided into two.
   • In plant cells, a cell plate forms, which eventually develops into a new cell wall separating the two daughter cells.

Summary of Stages of Mitosis:

Stage	Key Events
Interphase	Preparation, DNA replication, cell growth
Prophase	Chromatin condenses into chromosomes, spindle forms, nuclear envelope dissolves
Metaphase	Chromosomes align at the equator, spindle fibers attach to centromeres
Anaphase	Sister chromatids are pulled apart toward opposite poles
Telophase	Chromosomes de-condense, new nuclear envelopes form
Cytokinesis	Cytoplasm divides, forming two distinct daughter cells

Diagrams of Mitosis

1. Prophase:
   • Chromosomes condense and become visible.
   • The nuclear membrane starts to dissolve.
   • Spindle fibers form.
2. Metaphase:
   • Chromosomes align at the metaphase plate.
   • Spindle fibers attach to the centromeres.
3. Anaphase:
   • Sister chromatids are separated and move toward opposite poles.
4. Telophase:
   • Chromosomes de-condense, and new nuclear membranes form.
5. Cytokinesis:
   • The cytoplasm divides, forming two separate daughter cells.

Conclusion

Mitosis is an essential process for growth, development, and cellular regeneration. It ensures the accurate division and distribution of chromosomes to daughter cells, maintaining genetic consistency. The stages of mitosis—prophase, metaphase, anaphase, telophase, and cytokinesis—ensure the proper division of genetic material and cytoplasm, respectively.