Mitosis is the process by which a eukaryotic cell nucleus splits in two, followed by division of the parent cell into two daughter cells. The purpose of mitosis is for growth and to replace worn-out cells. During mitosis, the DNA in the cells nucleus is split into two equal sets of chromosomes, ensuring that each daughter cell gets a perfect, full set of chromosomes. Mitosis consists of five morphologically distinct phases: prophase, prometaphase, metaphase, anaphase, and telophase. Each phase involves characteristic steps in the process of chromosome alignment and separation. Once mitosis is complete, the entire cell divides in two by way of the process called cytokinesis. The five phases of mitosis are:
-
Prophase: During this phase, the parent cell chromosomes condense and become thousands of times more compact than they were during interphase. The spindle tubules extend from structures called centrosomes, with one centrosome located at each of the opposite ends, or poles, of a cell. The spindle tubules then attach to the chromosomes, which have already duplicated their DNA and aligned across the center of the cell.
-
Prometaphase: During this phase, the nuclear membrane breaks apart, and the spindle fibers attach to the chromosomes. The chromosomes line up neatly end-to-end along the center (equator) of the cell.
-
Metaphase: During this phase, the chromosomes are aligned at the equator of the cell, and the spindle fibers attach to each of the sister chromatids.
-
Anaphase: During this phase, the spindle fibers shorten and the centromere divides so that each chromosome becomes two separate chromatids. The sister chromatids are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole.
-
Telophase: During this phase, at each pole of the cell, a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new nuclei. The single cell then divides into two daughter cells.
In summary, mitosis is a highly regulated process involving hundreds of different cellular proteins, and it ensures that each daughter cell gets a perfect, full set of chromosomes.
