Mitosis - SS1 Biology Lesson Note
Mitosis is a type of cell division that occurs in somatic cells (non-reproductive cells) of eukaryotic organisms. It is a fundamental process in cellular reproduction and is responsible for the growth, development, and maintenance of tissues and organs.
During mitosis, a single parent cell divides into two genetically identical daughter cells. The process of mitosis can be divided into distinct stages:
1. Interphase: The cell undergoes a period of growth and preparation for division. During interphase, the cell carries out its normal metabolic activities and duplicates its DNA to ensure that each daughter cell receives a complete set of genetic material.
2. Prophase: The first stage of mitosis, during which the duplicated chromosomes condense and become visible under a microscope. The nuclear envelope begins to disassemble, and the mitotic spindle, a structure made of microtubules, starts to form.
3. Prometaphase: The nuclear envelope completely disintegrates, and the spindle fibers attach to the condensed chromosomes. The chromosomes become more compact and are now fully visible as two sister chromatids held together by a structure called the centromere.
4. Metaphase: The chromosomes align along the equator of the cell, forming a metaphase plate. The spindle fibers from opposite poles attach to the centromeres of each chromosome, ensuring proper alignment and equal distribution of genetic material.
5. Anaphase: The sister chromatids separate and are pulled apart towards opposite poles of the cell by the shortening spindle fibers. Each chromatid is now considered an individual chromosome.
6. Telophase: The separated chromosomes reach the opposite poles of the cell. Nuclear envelopes begin to form around each set of chromosomes, and the spindle fibers start to disassemble. The chromosomes start to decondense, returning to their extended, less visible state.
7. Cytokinesis: Cytokinesis is the final stage of cell division and involves the physical separation of the cytoplasm and organelles between the two daughter cells. In animal cells, a contractile ring of actin and myosin filaments forms and pinches the cell membrane inward, resulting in the formation of a cleavage furrow. In plant cells, a cell plate forms at the equator of the cell, which eventually develops into a new cell wall, dividing the cell into two daughter cells.
At the end of mitosis, two genetically identical daughter cells are formed, each with the same number of chromosomes as the parent cell. These daughter cells can then enter interphase and continue their normal cellular activities or undergo further rounds of division.
Mitosis plays a critical role in various biological processes, including embryonic development, tissue growth and repair, and asexual reproduction in some organisms. It ensures that each daughter cell receives a complete set of chromosomes and maintains the genetic stability of the organism.