Mada za sehemu hiiGrowth And DevelopmentMada 5
Mitosis is a process of cell division where a single cell divides to produce two genetically identical daughter cells. It ensures the preservation of chromosome number in each daughter cell, making it crucial for growth, development, and repair in multicellular organisms and for reproduction in unicellular organisms.
The cell cycle comprises five main phases:
- Growth Phase I (G1): A period of cell growth and preparation for DNA replication.
- Synthesis Phase (S): DNA replication occurs, doubling the genetic material.
- Growth Phase II (G2): Preparation for mitosis, including the synthesis of proteins required for division.
- Mitosis (M Phase): Division of the nucleus.
- Cytokinesis: Division of the cytoplasm and separation of daughter cells.
The first three phases (G1, S, and G2) together form the interphase, where the cell prepares for division.
Interphase
- Not part of mitosis but critical for preparation.
- Chromosomes are not visible and exist as chromatin.
- DNA replication and cell organelle synthesis occur.
Prophase
- Chromosomes condense and become visible as short, thick threads.
- In animal cells, centrioles move to opposite poles, forming spindle fibers.
- The nuclear envelope and nucleolus disintegrate.
Metaphase
- Chromosomes align at the cell's equator.
- Spindle fibers attach to centromeres.
Anaphase
- Centromeres split, separating sister chromatids.
- Chromatids are pulled to opposite poles by spindle fibers.
Telophase
- Chromatids reach the poles and uncoil into chromatin.
- Nuclear envelope and nucleolus reappear.
- Spindle fibers disappear, forming two nuclei.
Cytokinesis
- Division of the cytoplasm begins after telophase.
- In animal cells, the cell membrane constricts inward to form cleavage furrows, separating the cells.
- In plant cells, a cell plate forms from Golgi vesicles, developing into a cell wall that separates the daughter cells.
The mitotic nuclear division occurs in both unicellular and multicellular organisms. This process is equally important in all groups of organisms. The significance of mitosis to living organisms is as follows:
- Maintains genetic stability because daughter cells are identical to parent cells.
- Enhances growth through an increase in the number of cells.
- It is a means of healing of wounds and replacement of worn-out cells.
- Enhances regeneration of part of an organism. For example, a lizard tail.
- Mitosis process is used as a means of reproduction by unicellular organisms such as protozoans, which reproduce asexually.
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