Mitosis is the process by which a eukaryotic cell divides its genetic material equally between two daughter cells. This ensures that each new cell receives a complete copy of the organism’s genome, which is necessary for growth, repair, and maintenance of an organism’s tissues. Mitosis occurs in somatic cells, which are non-reproductive cells that make up the majority of an organism’s tissues and organs.
Mitosis consists of several distinct phases that occur in a specific sequence:
- Interphase: Although not technically a part of mitosis, interphase is the phase during which the cell spends most of its time preparing for cell division. Interphase is divided into three sub-phases: G1 (first gap), S (synthesis), and G2 (second gap). During the G1 and G2 phases, the cell grows and produces necessary proteins, while during the S phase, the DNA is replicated to ensure each daughter cell receives an identical copy of the genome.
- Prophase: The first stage of mitosis, during which the chromosomes condense and become visible under a light microscope. The centrosomes (microtubule-organizing centers) move to opposite poles of the cell, and the microtubules begin to form the mitotic spindle.
- Prometaphase: The nuclear envelope breaks down, and the microtubules of the mitotic spindle attach to the chromosomes at their kinetochores (protein structures on the centromere). The chromosomes begin to move toward the center of the cell, known as the equatorial plane.
- Metaphase: The chromosomes align along the equatorial plane, forming the metaphase plate. This ensures that each daughter cell will receive an equal and complete set of chromosomes during cell division.
- Anaphase: The sister chromatids (identical copies of each chromosome) are pulled apart by the spindle fibers and move toward opposite poles of the cell. This separation ensures that each daughter cell will receive an identical set of chromosomes.
- Telophase: The separated chromatids reach the opposite poles of the cell, and the nuclear envelope begins to reform around the chromosomes. The chromosomes decondense, and the mitotic spindle disassembles.
- Cytokinesis: The final stage of cell division, during which the cytoplasm divides and the cell membrane pinches inward to form two separate daughter cells. In animal cells, this process involves the formation of a contractile ring of actin and myosin filaments, called the cleavage furrow. In plant cells, a cell plate forms between the two daughter cells, eventually becoming the new cell wall.
Upon completion of mitosis and cytokinesis, the two daughter cells enter interphase and begin the process anew. Each daughter cell contains an identical copy of the parent cell’s genome, allowing for the continued growth and maintenance of an organism’s tissues.