The long strands of DNA found within a cell is packaged in a very compact form, known as a chromosome. Even in the most simple of creatures, DNA is quite long and without this compact packaging, there would be nowhere for the DNA to be stored. A special substance, known as chromatin, helps condense and compact the chromosomes found within the nucleus of a cell. Two double-helices form within the nucleus and join to one another. These two helices are known as sister-chromatids.
Each species has it’s own specific number of chromosomes found within its cells. Humans contain 46 different chromosomes. Somatic cells are the cells within the body that are not intended for reproduction, as eggs and sperm are. The cells of a somatic cell of a specific species, when displayed, is known as a karotype of that species.
Nearly all eukaryotes contained matched pairs of each and every chromosome within the somatic cells. These matched pairs are thought to be homologous pairs. For example, humans contain 46 chromosomes; 23 homologous pairs composed of 23 chromosomes from the mother and 23 chromosomes from the father.
The first stage of mitosis is known as prophase; a phase in which chromosomes begin to be compacted. During prophase, two structures within the cytoskeleton known as centrosomes begin to travel through the cytosol, with proteins growing along these centrosomes as they travel to the opposite side of the cell. These proteins, in combination with the centrosomes, may arrange themselves into what is known as a mitotic spindle.
The membrane of the nucleus, known as the nuclear envelope, breaks down towards the end of prophase during yet another phase known as prometaphase. The chromosomes within the nucleus are then attached to the microtubules projecting from the mitotic spindle.
During metaphase, the chromosomes of the cell line up along the midline of the cell, also known as the cell plate.
During anaphase, the sister-chromatids are broken apart and are then distributed on opposite sides of the cell, thus evenly dispersing the materials found within the cell, prior to division.
During telophase, a nuclear envelope begins to develop around each set of chromosomes. As the nuclear envelope continues to develop, the chromosomes within it begin to unfold. The components of a cell wall begin to accumulate along the cell plate, creating two new plasma membranes.
Cain, Michael L., Carol Kaesuk Yoon, and Anu Cundy. Discover biology . 4th ed. New York: W.W. Norton & Co., 2009. Print.
Cell Division: Mitosis