Mitosis is the process in which the nucleus of a cell divides to create two new nuclei, each containing an identical copy of DNA. Mitosis ensures that exact copies of DNA are passed on to the daughter cells. According to Rick Groleau from NOVA Science, almost all of the DNA duplication in the human body is carried out by mitosis.
Interphase is technically not part of mitosis, it is a phase of the cell cycle, as indicated by Developmental Biology Online. However, interphase is important in the build up to cell division, as the cell prepares for mitosis by replicating its DNA.
The Center for Research on Parallel Computation at Rice University website demonstrates, how, during prophase, the nucleolus disappears, while the chromatin becomes tightly coiled and begins to condense into chromosomes. The chromosomes then line up in pairs, joined at the centromere, forming an "X" shape. Spindle fibres, important in the subsequent stages of mitosis. begin to form in the cytoplasm. Furthermore, centrioles form and begin to move to opposite ends of the cell.
The start of prometaphase is marked by the the nuclear membrane breaking down, as explained by scientists at the Department of Biochemistry and Molecular Biophysics, University of Arizona. Once this occurs, proteins attach the centromeres, creating kinetochores. The kinetochores are connected by the spindle fibres and the chromosomes begin moving.
During metaphase the chromosomes are aligned along the middle of the cell nucleus by the spindle fibres. This is referred to as the metaphase plate. According to the University of Arizona Department of Biochemistry and Molecular Biophysics Department, this process ensures that during anaphase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.
During anaphase the paired chromosomes, containing an identical copy of DNA, are separated and begin to move to opposite ends of the cell, along the spindle fibres.
The chromosomes reach opposite ends of the cell and new membranes form around the daughter nuclei. The spindle fibres disperse and so do the chromosomes, which are no longer visible under a light microscope, according to the University of Arizona, Department of Biochemistry and Molecular Biophysics Department.
In a human cell, cytokinesis occurs when a fibre ring, composed of a protein called actin, forms around the center of the cell, as illustrated on the University of Arizona, Department of Biochemistry and Molecular Biophysics Department website. This fibre ring contracts, causing the cell to split into two daughter cells, each with one nucleus and an identical copy of DNA.
- Rick Groleau from NOVA Science: How Cells Divide: Mitosis vs. Meiosis
- Developmental Biology Online: Mitosis
- Center for Research on Parallel Computation at Rice University: Stages of Mitosis
- Department of Biochemistry and Molecular Biophysics, University of Arizona: The Cell Cycle and Mitosis Tutorial
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