5 Stages of Cell Division
Two types of cell division exist: meiosis, the division of sex cells that reduces the number of chromosomes (genetic material) by half, and mitosis, which is the type that most people refer to when speaking of cell division. Mitosis, the fundamental process of life according to the Genetics Home Reference, is the process by which the cell duplicates its chromosomes and divides into two identical daughter cells 1. The actual process of cell division is divided into five distinct stages in addition to a preparatory phase known as interphase and the actual splitting of the cells, known as cytokinesis.
During interphase, the DNA (deoxyribose nucleic acid) replicates and forms chromatin, which is the mass of genetic material that forms into chromosomes. The main difference between interphase and the first stage of mitosis is that the chromatin is diffuse and unorganized, according to Nature Education.
Prophase, the first stage of cell division, occurs when the chromatin coils and condenses to form the chromosomes. During this stage, the chromosomes are visible under a microscope showing the two chromatids (strands) connected by a centromere. The nuclear membrane inside the cell begins to disappear during this phase, marking the beginning of the next stage of division.
Prometaphase is the stage of cell division characterized by the complete disappearance of the nuclear membrane. This is an important step for the remaining stages because the centrosomes, the parts (one on each side) of the cell that organize the proteins that form the spindle fibers, need to gain access to the chromosomes. By the end of the prometaphase stage, these protein fibers attach to the centromeres of the chromosomes and begin pulling them.
During metaphase, the spindle protein fibers pull on the centromeres of the chromosomes, causing them to align along the middle of the cell. This middle point of the cell is referred to as either the metaphase plate, as described by the University of Arizona, or the equatorial plate as described by Thinkquest.com 2. The chromosomes must line up in order to enter the next stage of cell division.
As the cells enter the stage known as anaphase, the spindle fibers begin to shorten. This pulls on the centromeres that connect the two chromatids of the chromosomes. The centromeres split, and the chromatids move toward the opposite sides of the cells.
As the chromatids reach the opposite sides of the cell, which occurs during the telophase stage, new membranes begin to form around them. The result is two daughter nuclei. Following telophase, the cell splits, a process known as cytokinesis.
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