Mitosis is a fundamental biological process where a single parent cell divides to create two genetically identical daughter cells. This cell division ensures each new cell receives an exact copy of the genetic material from the original cell. Mitosis facilitates growth, repair, and the replacement of cells within an organism, maintaining genetic stability across cell generations.
Prophase
Prophase marks the initial stage of mitosis. During this phase, the cell’s genetic material, existing as diffuse chromatin, starts to condense tightly. This condensation makes individual chromosomes, each duplicated and consisting of two sister chromatids joined at a centromere, visible.
As chromosomes become more compact, the nuclear envelope begins to break down. Concurrently, the mitotic spindle, composed of microtubules, starts to form. These spindle fibers originate from centrosomes, which move to opposite poles of the cell, establishing the framework for chromosome separation.
Metaphase
Metaphase is characterized by the precise alignment of chromosomes. Spindle fibers fully extend and attach to the centromere of each sister chromatid at specific protein structures called kinetochores.
The spindle fibers then guide the chromosomes to align along the cell’s equatorial plane. This central line, known as the metaphase plate, represents an imaginary plane equidistant from the two spindle poles. This arrangement ensures each daughter cell receives an equal and complete set of chromosomes.
Anaphase
Anaphase is a dynamic stage where duplicated chromosomes are pulled apart. The defining event is the separation of sister chromatids, which are now considered individual chromosomes. This separation occurs as the cohesin proteins holding them together at the centromere are cleaved.
Once separated, these newly independent chromosomes are pulled towards opposite poles of the cell. The movement is driven by the shortening of the kinetochore microtubules. Concurrently, the non-kinetochore microtubules lengthen, pushing the poles further apart and elongating the cell.
Telophase
Telophase is the final stage of nuclear division in mitosis, reversing many prophase events. As separated chromosomes arrive at opposite poles, they begin to decondense. A new nuclear envelope forms around each set of chromosomes, creating two distinct nuclei within the single parent cell.
The mitotic spindle apparatus also disassembles. Cytoplasmic division, known as cytokinesis, typically begins during telophase or shortly after. Cytokinesis divides the cytoplasm and organelles, resulting in two separate daughter cells, each with its own nucleus and identical genetic material.
The Importance of Mitosis
Mitosis underpins the existence and continuity of multicellular organisms. It is the primary mechanism for growth, allowing a single-celled zygote to develop into a complex organism by increasing cell number. Mitosis also plays a role in tissue repair and regeneration.
Mitosis continuously replaces old or damaged cells, maintaining tissue and organ integrity. In some organisms, mitosis is a form of asexual reproduction, enabling them to produce genetically identical offspring.