Mitosis

Mitosis

  • Mitosis is the process of cell division that results in the formation of two genetically identical daughter cells.
  • It is crucial for growth, development, and tissue repair in multicellular organisms.

Phases of Mitosis:

  1. Prophase:

    • Chromosome Condensation:
      • Chromosomes, consisting of two sister chromatids, condense and become visible under the light microscope.
    • Nuclear Envelope Breakdown:
      • The nuclear envelope disintegrates, allowing the spindle fibers to access the chromosomes.
    • Centrosome Movement:
      • The centrosomes, containing the microtubule-organizing centers (MTOCs), move to opposite poles of the cell.
    • Spindle Fiber Formation:
      • Microtubules organize into spindle fibers extending from the centrosomes.

 

  1. Metaphase:

    • Chromosomal Alignment:
      • Chromosomes align along the metaphase plate, an imaginary plane equidistant between the two spindle poles.
    • Spindle Fiber Attachment:
      • Spindle fibers attach to the centromeres of each chromosome, connecting them to the opposite poles.

 

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  1. Anaphase:

    • Chromatid Separation:
      • Centromeres split, and sister chromatids are pulled apart toward opposite spindle poles.
    • Microtubule Shortening:
      • Microtubules shorten, facilitating the movement of chromatids.
    • Chromosome Migration:
      • Chromosomes move towards the poles, ensuring that each daughter cell receives a complete set of chromosomes.

 

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  1. Telophase:

    • Chromosome Decondensation:
      • Chromosomes reach the spindle poles and begin to decondense, becoming less visible.
    • Nuclear Envelope Reformation:
      • Nuclear envelopes re-form around the separated chromatids, creating two distinct nuclei.
    • Spindle Disintegration:
      • The mitotic spindle disintegrates.

 

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Telophase

Cytokinesis:

  • Cytokinesis is the division of the cytoplasm and organelles to produce two daughter cells.
  • In animal cells, a cleavage furrow forms as the cell membrane pinches inward.
  • In plant cells, a cell plate forms at the center and develops into a new cell wall.

 

Cytokinesis in animal and plant cells with diagram

 

Key Concepts:

  1. Chromosome Number:

    • Daughter cells have the same chromosome number (diploid) as the parent cell.
  2. Genetic Identity:

    • Daughter cells are genetically identical to each other and to the parent cell.
  3. Regulatory Proteins:

    • Cyclins and cyclin-dependent kinases (CDKs) regulate the progression through mitosis.
  4. Mitotic Index:

    • The mitotic index is the ratio of dividing cells to the total number of cells, providing an indication of the rate of cell division.

Significance of Mitosis:

  1. Growth and Development:

    • Mitosis is crucial for the growth and development of multicellular organisms.
    • It ensures the increase in the number of cells during embryonic development and throughout the life of an organism.
  2. Tissue Repair and Maintenance:

    • Mitosis plays a key role in tissue repair and maintenance.
    • It allows for the replacement of damaged or dead cells, contributing to the overall health and integrity of tissues.
  3. Genetic Stability:

    • Mitosis produces daughter cells that are genetically identical to the parent cell.
    • Ensures the stability of the organism's genetic makeup from one generation of cells to the next.
  4. Asexual Reproduction:

    • Mitosis is the basis for asexual reproduction in certain organisms.
    • It leads to the formation of genetically identical offspring from a single parent organism.
  5. Cell Renewal:

    • Cells that have a high turnover rate, such as those in the skin and digestive tract, undergo frequent mitosis to replace old and worn-out cells.
  6. Embryonic Development:

    • Mitosis is essential during the early stages of embryonic development.
    • It contributes to the formation of the blastocyst and subsequent tissue differentiation.
  7. Mitotic Index:

    • The mitotic index, or the ratio of dividing cells to the total number of cells, is an important indicator of the rate of cell division in tissues.
    • It is used to assess the growth status and activity of tissues.
  8. Regulation of Cell Cycle:

    • Mitosis is part of the overall cell cycle, which is tightly regulated by various proteins and checkpoints.
    • Ensures that cell division occurs under appropriate conditions and that DNA is replicated accurately.
  9. Prevention of DNA Damage:

    • Mitotic checkpoints, such as the G2 checkpoint, prevent cells with damaged DNA from entering mitosis.
    • Helps maintain genomic stability and prevent the propagation of mutations.
  10. Role in Cancer:

    • Dysregulation of mitosis and the cell cycle is a characteristic feature of cancer.
    • Understanding mitosis is crucial for developing targeted therapies that aim to control aberrant cell division in cancer cells.