The kinetochore is a structure on the centromere of chromosomes involved in mitosis and meiosis. It helps move chromosomes during cell division. Mitosis has four phases, and kinetochores play a role in the first three. During anaphase, sister chromatids divide into individual daughter chromosomes and migrate to each pole of the cell. In telophase, the cell rearranges itself around both sets of chromosomes and divides into two daughter cells through cytokinesis.
The kinetochore is a structure in the nucleus of a cell that is involved in mitosis and meiosis, the two processes of cell division. Kinetochores are specialized regions located on the centromeres of chromosomes and are made up of many types of proteins. The main function of the kinetochores is to help the movement of chromosomes during cell division. During mitosis, kinetochores act as handles on chromosomes. The fibers attach and pull on these “handles” to move the chromosomes within the dividing cell.
Mitosis is the process of cell division in somatic or nonsex cells. Meiosis is the process in which the sex cells, sperm and egg cells, divide. There are four phases of mitosis: prophase, metaphase, anaphase and telophase. The kinetochores play a role in the first three stages.
Before mitosis, the cell makes one copy of all of its DNA in the nucleus and a second pair of centrioles. During prophase, the newly copied material condenses into chromosomes. There are 46 chromosomes, each with two matching or sister chromatids held together in the middle by a centromere. The kinetochores are found on either side of the centromere.
The nuclear envelope then breaks down, allowing the cell’s structures to move freely within the entire cell. Then each pair of centrioles moves towards one end, or pole, of the cell. As they move, elongated microtubules, or spindle fibers, sprout out to help propel them forward. Some of the spindle fibers extend and connect to a kinetochore on either side of the centromere. The spindle fibers pull and tug on the kinetochores until all the chromosomes are aligned in the center of the cell.
During metaphase, the spindle fibers form a lemon-shaped matrix. This is called the mite spindle. The fibers are connected to the kinetochores along the midline of the cell and are anchored to the plasma membrane at each end of the cell.
Sister chromatids are divided in two at the centromere during anaphase. They divide into individual daughter chromosomes and each is still attached to the mitotic spindle at the kinetochore. A daughter chromosome migrates to each pole of the cell. Migration is accomplished by a motor protein in the kinetochore moving down the spindle fibers. The fibers are then taken apart or “chewed” to the pile.
In the final stage of mitosis, telophase, the cell rearranges itself around both sets of chromosomes. It prepares to divide into two similar cells. The chromosomes uncoil and the kinetochores and spindle break apart and vanish. The cell then goes through a process of cytokinesis, where it completely divides into two daughter cells.
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