Mitosis
is the process of cell division or growing more cells. Before a cell can divide, it must
replicate
its DNA. Prior to replicating the DNA, the chromosomes grow and prepare themselves for DNA replication in the
G1
phase. The chromosomes replicate themselves in the S or
G1
phase of the cell cycle. After the S phase, the cell goes through the
cytokinesis
phase where it prepares itself for mitosis. The G1, S, and G2 stages are collectively called
interphase
. The first stage of mitosis involves the condensing of chromosomes and the disappearance of the nuclear envelope; this stages is known as
prophase
. In the
metaphase
stage, the sister chromatids align on an equatorial plate. The sister chromatids separate and each chromosome moves to an opposite pole during
telophase
. During
mitosis
, the chromatin expands, the nuclear envelope reappears, and the two nuclei appear in the cell. During
telophase
, the cytoplasm divides, and the cell splits into two cells. Mitosis occurs in eukaryotic cells; a similar process called
binary fission
occurs in prokaryotic cells.
Mitosis is a crucial process that allows organisms to grow, develop, and replace damaged or old cells. It ensures that each new cell receives an identical copy of the parent cell's DNA. The process of mitosis can be divided into several stages.
1. Interphase: This is the preparatory phase where the cell spends most of its time. It consists of three subphases - G1, S, and G2. During G1, the cell carries out its normal functions and grows in size. In the S phase, the DNA is replicated, resulting in two identical copies of each chromosome. Finally, during G2, the cell continues to grow and prepare for division.
2. Prophase: This is the first stage of mitosis. The chromatin, a loose form of DNA, condenses and becomes visible as chromosomes. The nuclear envelope disappears, and the centrioles move to opposite poles of the cell, forming the spindle fibers.
3. Metaphase: The chromosomes align themselves along the equatorial plane of the cell, called the metaphase plate. The spindle fibers attach to the centromere region of each chromosome, ensuring they are correctly positioned for separation.
4. Anaphase: In this stage, the sister chromatids separate at the centromere and move towards opposite poles of the cell. The spindle fibers contract, pulling the chromatids to their respective poles. Each chromatid is now considered a separate chromosome.
5. Telophase: The chromosomes reach their respective poles, and a new nuclear envelope begins to form around each set of chromosomes. The chromosomes start to decondense, returning to the more relaxed chromatin form.
6. Cytokinesis: This is the final stage of cell division. The cytoplasm of the cell divides, resulting in the formation of two separate daughter cells, each with the same number of chromosomes as the parent cell. In animal cells, a cleavage furrow forms and pinches the cell membrane inward. In plant cells, a cell plate forms in the middle of the cell, which eventually becomes the cell wall.
It is important to note that mitosis occurs in eukaryotic cells, which have a nucleus and membrane-bound organelles. In contrast, prokaryotic cells, such as bacteria, undergo binary fission, a simpler form of cell division where the DNA replicates and the cell splits into two identical daughter cells.